Exercise and body weight: Difference between revisions

From Citizendium
Jump to navigation Jump to search
imported>Emily Moore
mNo edit summary
 
(26 intermediate revisions by 5 users not shown)
Line 1: Line 1:
{{CZ:(U00984) Appetite and Obesity, University of Edinburgh 2009/EZnotice}}
{{subpages}}
{{subpages}}
 
'''Exercise and body weight''' refers to the evidence that exercise is linked to a long-term reduction in body weight, and the controversy involved.
'''Exercise and body weight; covering the evidence that exercise is linked to a long-term reduction in body weight and the controversy and debate involved.'''
{{Image|figure 1.jpg|right|600px| }}
 
Excessive [[adiposity]] now affects more than one billion people worldwide.<ref name=one>Redinger RN (2009) Fat storage and the biology of energy expenditure ''Translational Research: J Lab Clin Med'' 154:52-60</ref> [[Adipose tissue]] is essential for energy use and heat production, but individuals with excess adiposity are at risk of serious co-morbidities including [[type II diabetes]], [[hypertension]] and cardiovascular diseases and many more.<ref name=one/>  <ref name=two>Catenacci VA, Wyatt HR (2007) The role of physical activity in producing and maintaining weight loss. ''Nat Clin Pract Endocrinol Metabol'' 3:518-29</ref>
{{CZ:(U00984) Appetite and Obesity, University of Edinburgh 2009/EZnotice}}
{{subpages}}
 
'''Exercise and body weight; covering the evidence that exercise is linked to a long-term reduction in body weight and the controversy and debate involved.'''
 
{{CZ:(U00984) Appetite and Obesity, University of Edinburgh 2009/EZnotice}}
{{subpages}}
 
'''Exercise and body weight; covering the evidence that exercise is linked to a long-term reduction in body weight and the controversy and debate involved.'''
 
{{CZ:(U00984) Appetite and Obesity, University of Edinburgh 2009/EZnotice}}
{{subpages}}
 
'''Exercise and body weight; covering the evidence that exercise is linked to a long-term reduction in body weight and the controversy and debate involved.'''
 
==Introduction==
Obesity and being overweight is currently an increasing problem affecting countries all over the world. Excessive [[adiposity]] now affects more than one billion people worldwide.<ref name=one>Redinger RN (2009) Fat storage and the biology of energy expenditure ''Translational Research: The Journal of Laboratory & Clinical Medicine'' 154:52-60</ref>
Adipose tissue is essential for energy use and heat production, but individuals with excess adiposity are at risk of developing co-morbidities such as [[type II diabetes]], [[hypertension]], [[insulin resistance]], cardiovascular diseases and many more.<ref name=one/>  Consequently, effective and successful interventions are needed to help individuals achieve and maintain a healthy body weight.<ref name=two>Catenacci VA, Wyatt HR (2007) The role of physical activity in producing and maintaining weight loss. ''Nature Clinical Practice Endocrinology & Metabolism'' 3:518-29</ref>
Excessive adiposity results from an imbalance in energy homeostasis. ''Energy balance'' is the difference between energy expenditure and energy intake; a negative energy balance will mean that body weight is lost over time, while a positive energy balance means that weight will be gained.<ref name=two/>  
Excessive adiposity results from an imbalance in energy [[homeostasis]]. ''Energy balance'' is the difference between energy expenditure and energy intake; a negative energy balance will mean that body weight is lost over time, while a positive energy balance means that weight will be gained.<ref name=two/> The brain is constantly readjusting [[metabolic rate]] and behavior to maintain a target weight (the "set point"; the level of body weight below which the brain triggers mechanisms to conserve energy stores, and above which the brain triggers mechanisms to consume energy). Diet and exercise may alter this set point, but only very slowly; metabolic adaptations to 'defend' the set point mean that it can be very difficult to maintain weight loss that has been achieved by an acute diet or by exercise.


{{Image|figure 1.jpg|center|600px|figure 1- Body weight homeostasis}}
There is controversy regarding the amount of physical activity necessary to facilitate weight loss maintenance. This article explores this debate and puts forward results supporting and opposing the positive relationship between exercise and body weight.<ref name=two/><ref name=three>Jakicic JM ''et al.''(2008) Effect of exercise on 24-month weight loss maintenance in overweight women ''Arch Int Med'' 168:1550-9</ref>


==The effect of exercise on the production and maintenance of long-term reduction in body weight ==
A [[meta-analysis]] of [[randomized controlled trial | randomized controlled trials]] by the international [[Cochrane Collaboration]] found that "exercise combined with diet resulted in a greater weight reduction than diet alone".<ref name="pmid17054187">{{cite journal |author=Shaw K ''et al.'' |title=Exercise for overweight or obesity |journal=Cochrane database of systematic reviews (Online) |volume=  |pages=CD003817 |year=2006 |pmid=17054187 |doi=10.1002/14651858.CD003817.pub3}}</ref> Use of a pedometer may assist in exercising for weight loss.<ref name="pmid18195317">{{cite journal |author=Richardson CR ''et al.'' |title=A meta-analysis of pedometer-based walking interventions and weight loss |journal=Ann Fam Med  |pages=69–77 |year=2008 |pmid=18195317 |doi=10.1370/afm.761}}</ref>


The brain is constantly readjusting [[metabolic rate]] and manipulating behavior in order to maintain a target weight; (the "set point"; the level of body weight below which the brain triggers mechanisms to conserve energy stores, and above which the brain triggers mechanisms to consume energy). Diet and exercise may alter the set point but only very slowly, biological mechanisms and metabolic adaptations to 'defend' the set point mean that maintaining weight loss that is achieved by an acute diet or by exercise can be very difficult.
===Exercise intensity and duration===
Increased physical activity can be effective in reducing body weight, but the optimal amount of exercise that will facilitate a long-term reduction in body weight is still unclear. Recent [[randomized controlled trials]] (RCTs) show only slight weight loss with physical activity intervention alone and little increase in weight loss combining exercise and dietary restriction.<ref name=two/> Some studies show that higher levels of exercise may result in greater weight loss.<ref name=three/>


There is controversy regarding the amount of physical activity necessary to facilitate weight loss maintenance. The following article explores this debate and puts forward results supporting and opposing the positive relationship between exercise and body weight.<ref name=two/><ref name=three>Jakicic JM, Marcus BH, Lang W, Janney C. (2008) Effect of exercise on 24-month weight loss maintenance in overweight women. Archives of Internal Medicine. 168:1550-9</ref>
Most recent studies show that a reduction in body weight of 1-3kg can be achieved over 4-16 months using exercise prescriptions of 60-180 min per week.<ref name=two/> <ref name=three/>,<ref name=four>Schoeller DA ''et al.'' (1997) How much physical activity is needed to minimize weight gain in previously obese women? ''Am J Clin Nutr'' 66:551-6</ref> Individuals achieving and sustaining a weight loss of 10% or more of their initial body weight after 24 months carried out more physical activity than those who maintained a weight loss of less than 10%.<ref name=three/>  


[[User:Katie Gallagher|Katie Gallagher]] 16:42, 12 November 2009 (UTC)
However, few studies of the amount of exercise required to augment long-term reduction in body weight have followed subjects for more than 6-12 months. This may be due to the challenging problems concerning overweight individuals in completing and adhering to increased levels of physical activity. In one study, <ref name=five>Donnelly JE, Smith BK (2005) Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences ''Exercise Sports Sci Rev'' 33:169-74</ref> fewer than half the number of individuals engaging in physical activity completed the 16 month study despite being compensated for taking part.


==The Effect of exercise on the production and maintenance of long-term reduction in body weight ==
Other factors influencing results include compensation mechanisms such as changes in resting metabolic rate as well as increased energy intake.<ref name=two/> Moreover, difficulties in interpreting results may arise when calculating body weight, as adipose tissue lost due to exercise may be overshadowed by an increase in lean muscle mass. Studies that measure body composition compared to body weight solely, illustrate that exercise “reduces abdominal visceral fat” and “improves cardio metabolic risk factors”.<ref name=two/> Consequently body weight may not be the best measure to evaluate the effects of physical activity on health. These results, and those of Schoeller ''et al.'',<ref name=four/> suggest that the level of exercise required to sustain weight loss is “approximately twice the public health recommendation,”  - at least 150 minutes of moderate intensity activity each week.<ref name=three/>


===Exercise intensity and duration on long-term weight loss===
===Maintenance of long-term weight loss===
After weight loss, subjects often regain the lost weight, and sometimes even overshoot their original weight.  Abderson ''et al.'' analysed a large number and variety of weight loss studies carried out in the USA, and concluded that more than 35% of lost weight is regained within the first year, and most is regained within five years.<ref>Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies ''Am J Clin Nutr'' 74:579-84</ref> Among other inputs, the reduced plasma concentrations of [[leptin]] and [[insulin]] that accompany a reduced fat mass  result in an increased [[appetite|drive to eat]] along with suppressed energy expenditure.  The body’s choice of fuel also changes within the [[diurnal cycle]] and is affected by lifestyle.  Therefore, to maintain their new weight, individuals need to limit their food intake to the same extent that expenditure is suppressed.


Increased levels of physical activity can be effective in reducing body weight, but the optimal amount of exercise that will facilitate a long-term reduction in body weight is still unclear. Recent [[randomized, controlled trials]] (RCTs) demonstrate slight weight loss with physical activity intervention alone and little increase in weight loss combining exercise and dietary restriction.<ref name=two/> Topical studies show that higher levels of exercise may result in greater weight loss.<ref name=three/>
Regular exercise may prevent or counter these metabolic adaptations that can lead to weight regain. MacLean ''et al.'' <ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am J Physiol'' 297:793-802</ref> showed that relapsing rats that exercised not only lost weight in liver and [[mesenteric fat pad]]s compared to sedentary counterparts, but did not succumb to the overeating normally seen after dramatic weight loss. The energy balance previously mentioned was delayed and much reduced (roughly 40%), therefore greatly reducing the rats’ desire to gorge themselves. Lean rats show a diurnal shift in fuel usage (favouring [[carbohydrate]]s during the dark phase and fat during the light phase). Obese rats did not present this shift. In sedentary rats, carbohydrates were favoured regardless, while fat was stored and increased [[lipogenesis]] was observed.


Most recent studies show that a reduction in body weight of 1-3kg can be achieved over 4-16 months using exercise prescriptions of 60-180 min per week.<ref name=two/> Jakicic ''et al.'' as well as other study groups, are interested in the effect of increased intensity (moderate vs vigorous) and duration (moderate vs. high) of exercise on long-term weight loss.<ref name=three/>,<ref name=four>Schoeller DA, Shay K, Kushner RF (1997) How much physical activity is needed to minimize weight gain in previously obese women? ''Am J Clin Nutr'' 66:551-6</ref> Individuals achieving and sustaining a weight loss of 10% or more of their initial body weight after 24 months carried out more physical activity than those who maintained a weight loss of less than 10%.<ref name=three/> This study demonstrates a correlation between increased leisure time activity and weight loss over time, concluding that 275 min/week (1500 kcal/week) is needed to sustain weight loss. This suggests that increased exercise intensity and duration may create a large negative energy balance resulting in substantial weight loss.
[[AMPK]] is a hypothalamic nutrient sensor that responds to low nutrient availability. Signals from the periphery (including the hormones leptin and [[insulin]]) were not increased by exercise regimes, but acute bouts of exercise lessen the response of AMPK to peripheral deprivation signals, thereby reducing the drive to overfeed.<ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss ''Am J Physiol'' 297:793-802</ref> Rats that had lost weight were observed to alternate massive overeating with periods of deprivation. Daily [[aerobic exercise]] reduced the extremes in fuel consumption that are associated with this phenomenon as well as the excessive desire to eat and/or hunger pains that are the downfall of many individuals after calorie-restricted weight loss.  Preventing the typical increase in [[adipocytes]] may affect the ability to store excess calories, as the peripheries are wired to process and store any fuel excess rapidly and efficiently to promote regain and return to the defended body weight.
 
However, few studies of the amount and intensity of exercise required to augment long-term reduction in body weight have followed subjects for more than 6-12 months. This may be due to the challenging problems concerning overweight individuals in completing and adhering to increased levels of physical activity. In a study conducted by Donnelly and Smith <ref name=five>Donnelly JE, Smith BK (2005) Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences. ''Exercise and sports sciences reviews'' 33:169-74</ref> less than half the number of individuals engaging in physical activity completed the 16 month study despite being compensated.<ref name=two/>
 
Other factors influencing results and energy balance may include compensation mechanisms such as changes in resting metabolic rate (RMR) as well as increased energy intake due to long-term augmented energy expenditure which may attenuate weight loss.<ref name=two/> Difficulties in interpreting results may arise when calculating body weight, as adipose tissue lost due to exercise may be overshadowed by an increase in lean muscle mass. Studies that measure body composition compared to body weight solely, illustrate that exercise “reduces abdominal visceral fat” and “improves cardio metabolic risk factors”.<ref name=two/> Consequently body weight may not be the best measure to evaluate the effects of physical activity on health.
 
The results mentioned above as well as being equivalent to results of Schoeller ''et al.'',<ref name=four/> suggest that appropriate levels of exercise required to sustain weight loss is “approximately twice the public health recommendation,” at least 150 minutes of moderate intensity activity per week.<ref name=three/>
 
===Maintenance of Long-Term Weight Loss===
Many studies have found that, after weight loss, subjects often regain the lost weight, and sometimes even overshoot their original weight.  Abderson ''et al.''analysed a large number and variety of weight loss studies carried out in the USA, and concluded that more than 35% of lost weight is regained within the first year, and most is regained within five years<ref>Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies. ''Am J Clin Nutr'' 74:579-84</ref>. Metabolism plays a key role in this. Among other inputs, the reduced plasma concentrations of [[leptin]] and [[insulin]] that accompany a reduced fat mass tell the brain that the body is energy-deficient, resulting in a drive to eat along with suppressed energy expenditure.  The body’s choice of fuel also changes within the diurnal cycle and is affected by lifestyle.  Therefore, to maintain their new weight, individuals need to limit their food intake to the same extent that expenditure is suppressed.
 
'''The role of exercise'''
 
There is evidence to suggest that regular exercise prevents or counters these metabolic adaptations that lead to weight regain. MacLean ''et al.'' <ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am J Physiol'' 297:793-802</ref> showed that relapsing rats that exercised not only that presented a reduction in weight in liver tissue and mesenteric fat pads compared to their sedentary counterparts, but did not succumb to the overeating normally seen after dramatic weight loss.
 
[NOT CLEAR TO ME WHAT YOU'RE SAYING HERE IN THIS SECTION]
 
The energy balance previously mentioned was delayed and much reduced (roughly 40%), therefore greatly reducing the rats’ desire to gorge themselves.  Lean rats show a diurnal shift in fuel usage (favouring [[carbohydrate]]s during the dark cycle and fat during the light).  Obese rats did not present this shift.  It however returned after weight loss.  (see if can find more on this)  In sedentary rats, carbohydrates were favoured regardless, while fat was stored and increased [[lipogenesis]] was observed. 
 
 
[[AMPK]] is a hypothalamic nutrient sensor (WHAT DO YOU MEAN BY THIS?) that responds to low nutrient availability. Signals from the periphery (including the hormones leptin and insulin) were not increased by exercise regimes. The reception of these signals, however, seems to be more involved. Acute bouts of exercise were shown by MacLean ''et al.'' to lessen the response of AMPK to peripheral deprivation signals, thereby reducing the drive to overfeed.<ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am. J Physiol'' 297:793-802</ref> Rats that had lost weight were observed to alternate massive overeating with periods of deprivation. Daily aerobic exercise reduced the extremes in fuel consumption that are associated with this phenomenon as well as the excessive desire to eat and/or hunger pains that are the downfall of many individuals after a calorie-restricted weight loss program.  The authors suggested that preventing the typical increase in [[adipocytes]] may affect the ability to store excess calories, as the peripheries are wired to process and store any fuel excess rapidly and efficiently to promote regain and return to the defended body weight. The drive to physical activity is tightly regulated and directly influences adiposity and body weight.


==Contradictory evidence for the link between exercise and a reduction in body weight ==
==Contradictory evidence for the link between exercise and a reduction in body weight ==
In 2004, it was reported that more than half of British adults are overweight, and that obesity among school children has increased by 70% in the past generation <ref>Jeffery AN ''et al.'' (2004) Parents’ awareness of overweight in themselves and their children: cross sectional study within a cohort (EarlyBird 21) ''BMJ''</ref> The correlation between increasingly sedentary lifestyles and the obesity epidemic has lead to a broad assumption that physical inactivity is to blame for the worldwide crisis. However, there is compelling evidence emerging to the contrary.


In 2004 it was reported that more than half of British adults are overweight, and that obesity among school children has increased by 70% in the past generation <ref>Jeffery AN ''et al.'' (2004) Parents’ awareness of overweight in themselves and their children: cross sectional study within a cohort (EarlyBird 21). ''BMJ''</ref> The correlation between increasingly sedentary lifestyles and the obesity epidemic has lead to a broad assumption that physical inactivity is to blame for the worldwide crisis. However, there is compelling evidence emerging to the contrary.
Perhaps the most reliable reports have been produced by the "EarlyBird" study at the Universities of Exeter and Plymouth.<ref>Metcalf BS ''et al.'' (2001) Technical reliability of the CSA activity monitor: The EarlyBird Study. ''Medicine & Science in Sports & Exercise'' 1533-7</ref> This 12 year cohort study, to be completed in 2013, involves measuring the physical activity and body composition of 300 children from the age of 5. Unlike other trials, physical activity was measured using an impressively precise CSA accelerometer-based activity monitor. Similar previous trials have depended on unreliable qualitative reports from parents or children.  One of their 56 peer reviewed articles finds no association between physical activity and BMI or body fat in either sex. <ref>Metcalf BS ''et al.'' (2008) Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37) ''Arch Dis Child'' 93:772-7</ref>


Perhaps the most reliable reports have been produced by the EarlyBird study, currently underway at the Universities of Exeter and Plymouth. <ref>Metcalf BS ''et al.'' (2001) Technical reliability of the CSA activity monitor: The EarlyBird Study. ''Medicine & Science in Sports & Exercise'' 1533-7</ref> This 12 year cohort study, to be completed in 2013, involves measuring the physical activity and body composition of 300 children from the age of 5. Unlike other trials, physical activity was measured using an impressively precise CSA accelerometer-based activity monitor. Similar previous trials have depended on unreliable qualitative reports from parents or children One of their 56 peer reviewed articles finds no association between physical activity and BMI or body fat in either sex <ref>Metcalf BS ''et al.'' (2008) Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37) ''Arch Dis Child'' 93: 772-7</ref>.
Increasing evidence suggests that children are intrinsically programmed to undertake a set level of activity per day, which is determined either genetically, or as a result of early childhood experience. Hence, it would be incorrect to implicate TV watching in any resulting daily energy surplus <ref>(Sonneville ''et al.'' (2008)</ref>. Adding further credence to this, recent results of EarlyBird suggest that it is obesity that makes children decreasingly active, and not inactivity that makes children obese.


Increasing evidence suggests that children are intrinsically programmed to undertake a set level of activity per day, which is determined either genetically, or as a result of an early childhood experience. Hence, it would be incorrect to implicate TV watching in any resulting daily energy surplus <ref>(Sonneville ''et al.'' (2008)</ref>. Adding further credence to this, results being published by EarlyBird in the near future suggest that it is obesity that makes children decreasingly active, and not inactivity that makes children obese.
A cluster randomised controlled trial was carried out in Glasgow, in which 545 pre-school children were subjected to a realistic level of enhanced activity per week, over 24 weeks. It was similarly deduced from this study that physical activity does not reduce BMI in young children <ref>Reilly JJ ''et al.''(2006) Physical activity to prevent obesity in young children: cluster randomised controlled trial ''BMJ'' </ref>. The same conclusion was reached  by Harris ''et al.'', who scrutinised 18 studies meeting inclusion criteria to explore the effect of school-based physical activity interventions on BMI in children. <ref>Harris ''et al.'' (2009)</ref>


A cluster randomised controlled trial was carried out in Glasgow, in which 545 pre-school children were subjected to a realistic level of enhanced activity per week, over 24 weeks. It was similarly deduced from this study that physical activity does not reduce BMI in young children <ref>Reilly JJ ''et al.''(2006) Physical activity to prevent obesity in young children: cluster randomised controlled trial. ''BMJ'' </ref>. The same conclusion was reached  by Harris ''et al.'' who scrutinised 18 studies meeting inclusion criteria to explore the effect of school-based physical activity interventions on BMI in children. <ref>Harris ''et al.'' (2009)</ref>
Such findings have not been exclusive to children. Church randomized 411 sedentary women to either 1 of 3 exercise groups of varying energy expenditure, or a non-exercise control group. He found that the group assigned to no exercise lost a similar amount of weight to the exercisers <ref>Church ''et al.'' (2009) Changes in weight, waist circumference and compensatory responses with different doses of exercise among sedendary, overweight postmenopausal women. ''PLoS ONE'' 4:1-11</ref>  
 
Such findings have not been exclusive to children. Church randomized 411 sedentary women to either 1 of 3 exercise groups of varying energy expenditure, or a non-exercise control group. He found that the group assigned to no exercise lost a similar amount of weight to the exercisers <ref>Church ''et al.'' (2009) Changes in weight, waist circumference and compensatory responses with different doses of exercise among sedendary, overweight postmenopausal women. ''PLoS ONE'' 4 (2):1-11.</ref>.
   
   
The explanation for this controversial evidence may depend on the observation that exercise increases appetite through orexigenic peptides such as NPY <ref>Lewis ''et al.'' (1993)</ref>. Caloric overcompensation is the result of our limited capacity to deal with excess calories, due to our minimal brown fat stores, the activation of orexigenic and reward pathways in the brain, and the tendency to underestimate calorie consumption. The frequent result is excessive dietary intake, resulting in an energy imbalance and net weight gain. This theory is supported by an 18-month study by Sonneville and Gortmaker involving 538 students who, on average, consumed 100 calories more than they had just expended following exercise <ref> Sonneville KR, Gortmaker SL (2008) Total energy intake, adolescent discretionary behaviours and the energy gap. ''Int J Obesity'' 32:19-27</ref>.
The explanation may depend on the observation that exercise increases appetite through orexigenic peptides such as NPY <ref>Lewis ''et al.'' (1993)</ref>. Caloric overcompensation is the result of our limited capacity to deal with excess calories, due to our minimal brown fat stores, the activation of orexigenic and reward pathways in the brain, and the tendency to underestimate calorie consumption. The frequent result is excessive dietary intake, resulting in an energy imbalance and net weight gain. This theory is supported by an 18-month study by Sonneville and Gortmaker involving 538 students who, on average, consumed 100 calories more than they had just expended following exercise <ref> Sonneville KR, Gortmaker SL (2008) Total energy intake, adolescent discretionary behaviours and the energy gap. ''Int J Obesity'' 32:19-27</ref>.
 
Although the link between exercise and weight loss is tenuous, one must not underestimate the potential benefits of exercise in not only preventing numerous diseases, but also in enhancing mental health and cognitive ability.


These findings suggest that, in the absence of the will-power to override the desire to consume surplus calories post exercise, the key to achieving a net daily energy deficit is not to increase exercise, but to limit daily calorie consumption.
These findings suggest that, in the absence of the will-power to override the desire to consume surplus calories post exercise, the key to achieving a net daily energy deficit is not to increase exercise, but to limit daily calorie consumption.
== '''Conclusion''' ==
There is a lot of contradictory evidence presented. For instance, if we are to look at the maintenance of a reduced body weight, we find plenty of arguments for and against exercise having a positive effect, not least due to the fact that the time period over which these studies were conducted ranged from 6 months to 3 years, whereas body weight has been shown to fluctuate up to 5 years after weight loss.  Parallel to this are the problems that obese subjects may encounter in adhering to an exercise program due to the inherent limitations of their condition.  Papers tend to concentrate on obese individuals, which does raise questions about the relevance of their statistics.   
It should be noted, however, that in many cases, results are seen, especially when counseling, group sessions, and interventions are included in the program.  Although it is not activity but resting metabolism that makes up the greatest energy expenditure within the body, it seems that exercise does indeed play a very important role in both preventing, reaching and defending a lower body weight.


==References==
==References==
<references/>
{{reflist | 2}}[[Category:Suggestion Bot Tag]]
 
http://www.earlybirddiabetes.org
 
The Times. ‘Exercise? A fat lot of good that is if you want to lose weight’. ''Times'' October 19th 2009.
 
Harris KC ''et al.''(2009) Effect of school-based physical activity interventions on body mass index in children: a meta-analysis. ''Can Med Ass J'' 180:719-26.
 
 
Lewis DE ''et al.'' (1993) Intense exercise and food restriction cause similar hypothalamic neuropeptide Y increases in rats. ''Ame J Physiol'' 264:279-84.
 
Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies  ''Am J Clin Nutrition''. 74:579-84.
 
==The Effect of exercise on the production and maintenance of long-term reduction in body weight ==
 
===Exercise intensity and duration on long-term weight loss===
 
Increased levels of physical activity can be effective in reducing body weight, but the optimal amount of exercise that will facilitate a long-term reduction in body weight is still unclear. Recent [[randomized, controlled trials]] (RCTs) demonstrate slight weight loss with physical activity intervention alone and little increase in weight loss combining exercise and dietary restriction.<ref name=two/> Topical studies show that higher levels of exercise may result in greater weight loss.<ref name=three/>
 
Most recent studies show that a reduction in body weight of 1-3kg can be achieved over 4-16 months using exercise prescriptions of 60-180 min per week.<ref name=two/> Jakicic ''et al.'' as well as other study groups, are interested in the effect of increased intensity (moderate vs vigorous) and duration (moderate vs. high) of exercise on long-term weight loss.<ref name=three/>,<ref name=four>Schoeller DA, Shay K, Kushner RF (1997) How much physical activity is needed to minimize weight gain in previously obese women? ''Am J Clin Nutr'' 66:551-6</ref> Individuals achieving and sustaining a weight loss of 10% or more of their initial body weight after 24 months carried out more physical activity than those who maintained a weight loss of less than 10%.<ref name=three/> This study demonstrates a correlation between increased leisure time activity and weight loss over time, concluding that 275 min/week (1500 kcal/week) is needed to sustain weight loss. This suggests that increased exercise intensity and duration may create a large negative energy balance resulting in substantial weight loss.
 
However, few studies of the amount and intensity of exercise required to augment long-term reduction in body weight have followed subjects for more than 6-12 months. This may be due to the challenging problems concerning overweight individuals in completing and adhering to increased levels of physical activity. In a study conducted by Donnelly and Smith <ref name=five>Donnelly JE, Smith BK (2005) Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences. ''Exercise and sports sciences reviews'' 33:169-74</ref> less than half the number of individuals engaging in physical activity completed the 16 month study despite being compensated.<ref name=two/>
 
Other factors influencing results and energy balance may include compensation mechanisms such as changes in resting metabolic rate (RMR) as well as increased energy intake due to long-term augmented energy expenditure which may attenuate weight loss.<ref name=two/> Difficulties in interpreting results may arise when calculating body weight, as adipose tissue lost due to exercise may be overshadowed by an increase in lean muscle mass. Studies that measure body composition compared to body weight solely, illustrate that exercise “reduces abdominal visceral fat” and “improves cardio metabolic risk factors”.<ref name=two/> Consequently body weight may not be the best measure to evaluate the effects of physical activity on health.
 
The results mentioned above as well as being equivalent to results of Schoeller ''et al.'',<ref name=four/> suggest that appropriate levels of exercise required to sustain weight loss is “approximately twice the public health recommendation,” at least 150 minutes of moderate intensity activity per week.<ref name=three/>
 
===Maintenance of Long-Term Weight Loss===
Many studies have found that, after weight loss, subjects often regain the lost weight, and sometimes even overshoot their original weight.  Abderson ''et al.''analysed a large number and variety of weight loss studies carried out in the USA, and concluded that more than 35% of lost weight is regained within the first year, and most is regained within five years<ref>Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies. ''Am J Clin Nutr'' 74:579-84</ref>. Metabolism plays a key role in this. Among other inputs, the reduced plasma concentrations of [[leptin]] and [[insulin]] that accompany a reduced fat mass tell the brain that the body is energy-deficient, resulting in a drive to eat along with suppressed energy expenditure.  The body’s choice of fuel also changes within the diurnal cycle and is affected by lifestyle.  Therefore, to maintain their new weight, individuals need to limit their food intake to the same extent that expenditure is suppressed.
 
'''The role of exercise'''
 
There is evidence to suggest that regular exercise prevents or counters these metabolic adaptations that lead to weight regain. MacLean ''et al.'' <ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am J Physiol'' 297:793-802</ref> showed that relapsing rats that exercised not only that presented a reduction in weight in liver tissue and mesenteric fat pads compared to their sedentary counterparts, but did not succumb to the overeating normally seen after dramatic weight loss.
 
[NOT CLEAR TO ME WHAT YOU'RE SAYING HERE IN THIS SECTION]
 
The energy balance previously mentioned was delayed and much reduced (roughly 40%), therefore greatly reducing the rats’ desire to gorge themselves.  Lean rats show a diurnal shift in fuel usage (favouring [[carbohydrate]]s during the dark cycle and fat during the light).  Obese rats did not present this shift.  It however returned after weight loss.  (see if can find more on this)  In sedentary rats, carbohydrates were favoured regardless, while fat was stored and increased [[lipogenesis]] was observed. 
 
 
[[AMPK]] is a hypothalamic nutrient sensor (WHAT DO YOU MEAN BY THIS?) that responds to low nutrient availability.  Signals from the periphery (including the hormones leptin and insulin) were not increased by exercise regimes.  The reception of these signals, however, seems to be more involved. Acute bouts of exercise were shown by MacLean ''et al.'' to lessen the response of AMPK to peripheral deprivation signals, thereby reducing the drive to overfeed.<ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am. J Physiol'' 297:793-802</ref> Rats that had lost weight were observed to alternate massive overeating with periods of deprivation. Daily aerobic exercise reduced the extremes in fuel consumption that are associated with this phenomenon as well as the excessive desire to eat and/or hunger pains that are the downfall of many individuals after a calorie-restricted weight loss program.  The authors suggested that preventing the typical increase in [[adipocytes]] may affect the ability to store excess calories, as the peripheries are wired to process and store any fuel excess rapidly and efficiently to promote regain and return to the defended body weight. The drive to physical activity is tightly regulated and directly influences adiposity and body weight.
 
==Contradictory evidence for the link between exercise and a reduction in body weight ==
 
In 2004 it was reported that more than half of British adults are overweight, and that obesity among school children has increased by 70% in the past generation <ref>Jeffery AN ''et al.'' (2004) Parents’ awareness of overweight in themselves and their children: cross sectional study within a cohort (EarlyBird 21). ''BMJ''</ref> The correlation between increasingly sedentary lifestyles and the obesity epidemic has lead to a broad assumption that physical inactivity is to blame for the worldwide crisis. However, there is compelling evidence emerging to the contrary.
 
Perhaps the most reliable reports have been produced by the EarlyBird study, currently underway at the Universities of Exeter and Plymouth. <ref>Metcalf BS ''et al.'' (2001) Technical reliability of the CSA activity monitor: The EarlyBird Study. ''Medicine & Science in Sports & Exercise'' 1533-7</ref> This 12 year cohort study, to be completed in 2013, involves measuring the physical activity and body composition of 300 children from the age of 5. Unlike other trials, physical activity was measured using an impressively precise CSA accelerometer-based activity monitor. Similar previous trials have depended on unreliable qualitative reports from parents or children  One of their 56 peer reviewed articles finds no association between physical activity and BMI or body fat in either sex <ref>Metcalf BS ''et al.'' (2008) Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37) ''Arch Dis Child'' 93: 772-7</ref>.
 
Increasing evidence suggests that children are intrinsically programmed to undertake a set level of activity per day, which is determined either genetically, or as a result of an early childhood experience. Hence, it would be incorrect to implicate TV watching in any resulting daily energy surplus <ref>(Sonneville ''et al.'' (2008)</ref>. Adding further credence to this, results being published by EarlyBird in the near future suggest that it is obesity that makes children decreasingly active, and not inactivity that makes children obese.
 
A cluster randomised controlled trial was carried out in Glasgow, in which 545 pre-school children were subjected to a realistic level of enhanced activity per week, over 24 weeks. It was similarly deduced from this study that physical activity does not reduce BMI in young children <ref>Reilly JJ ''et al.''(2006) Physical activity to prevent obesity in young children: cluster randomised controlled trial. ''BMJ'' </ref>. The same conclusion was reached  by Harris ''et al.'' who scrutinised 18 studies meeting inclusion criteria to explore the effect of school-based physical activity interventions on BMI in children. <ref>Harris ''et al.'' (2009)</ref>
 
Such findings have not been exclusive to children. Church randomized 411 sedentary women to either 1 of 3 exercise groups of varying energy expenditure, or a non-exercise control group. He found that the group assigned to no exercise lost a similar amount of weight to the exercisers <ref>Church ''et al.'' (2009) Changes in weight, waist circumference and compensatory responses with different doses of exercise among sedendary, overweight postmenopausal women. ''PLoS ONE'' 4 (2):1-11.</ref>.
The explanation for this controversial evidence may depend on the observation that exercise increases appetite through orexigenic peptides such as NPY <ref>Lewis ''et al.'' (1993)</ref>. Caloric overcompensation is the result of our limited capacity to deal with excess calories, due to our minimal brown fat stores, the activation of orexigenic and reward pathways in the brain, and the tendency to underestimate calorie consumption. The frequent result is excessive dietary intake, resulting in an energy imbalance and net weight gain. This theory is supported by an 18-month study by Sonneville and Gortmaker involving 538 students who, on average, consumed 100 calories more than they had just expended following exercise <ref> Sonneville KR, Gortmaker SL (2008) Total energy intake, adolescent discretionary behaviours and the energy gap. ''Int J Obesity'' 32:19-27</ref>.
 
Although the link between exercise and weight loss is tenuous, one must not underestimate the potential benefits of exercise in not only preventing numerous diseases, but also in enhancing mental health and cognitive ability.
 
These findings suggest that, in the absence of the will-power to override the desire to consume surplus calories post exercise, the key to achieving a net daily energy deficit is not to increase exercise, but to limit daily calorie consumption.
 
== '''Conclusion''' ==
There is a lot of contradictory evidence presented. For instance, if we are to look at the maintenance of a reduced body weight, we find plenty of arguments for and against exercise having a positive effect, not least due to the fact that the time period over which these studies were conducted ranged from 6 months to 3 years, whereas body weight has been shown to fluctuate up to 5 years after weight loss.  Parallel to this are the problems that obese subjects may encounter in adhering to an exercise program due to the inherent limitations of their condition.  Papers tend to concentrate on obese individuals, which does raise questions about the relevance of their statistics.   
 
It should be noted, however, that in many cases, results are seen, especially when counseling, group sessions, and interventions are included in the program.  Although it is not activity but resting metabolism that makes up the greatest energy expenditure within the body, it seems that exercise does indeed play a very important role in both preventing, reaching and defending a lower body weight.
 
==References==
<references/>
 
http://www.earlybirddiabetes.org
 
The Times. ‘Exercise? A fat lot of good that is if you want to lose weight’. ''Times'' October 19th 2009.
 
Harris KC ''et al.''(2009) Effect of school-based physical activity interventions on body mass index in children: a meta-analysis. ''Can Med Ass J'' 180:719-26.
 
 
Lewis DE ''et al.'' (1993) Intense exercise and food restriction cause similar hypothalamic neuropeptide Y increases in rats. ''Ame J Physiol'' 264:279-84.
 
Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies  ''Am J Clin Nutrition''. 74:579-84.
 
==The Effect of exercise on the production and maintenance of long-term reduction in body weight ==
 
===Exercise intensity and duration on long-term weight loss===
 
Increased levels of physical activity can be effective in reducing body weight, but the optimal amount of exercise that will facilitate a long-term reduction in body weight is still unclear. Recent [[randomized, controlled trials]] (RCTs) demonstrate slight weight loss with physical activity intervention alone and little increase in weight loss combining exercise and dietary restriction.<ref name=two/> Topical studies show that higher levels of exercise may result in greater weight loss.<ref name=three/>
 
Most recent studies show that a reduction in body weight of 1-3kg can be achieved over 4-16 months using exercise prescriptions of 60-180 min per week.<ref name=two/> Jakicic ''et al.'' as well as other study groups, are interested in the effect of increased intensity (moderate vs vigorous) and duration (moderate vs. high) of exercise on long-term weight loss.<ref name=three/>,<ref name=four>Schoeller DA, Shay K, Kushner RF (1997) How much physical activity is needed to minimize weight gain in previously obese women? ''Am J Clin Nutr'' 66:551-6</ref> Individuals achieving and sustaining a weight loss of 10% or more of their initial body weight after 24 months carried out more physical activity than those who maintained a weight loss of less than 10%.<ref name=three/> This study demonstrates a correlation between increased leisure time activity and weight loss over time, concluding that 275 min/week (1500 kcal/week) is needed to sustain weight loss. This suggests that increased exercise intensity and duration may create a large negative energy balance resulting in substantial weight loss.
 
However, few studies of the amount and intensity of exercise required to augment long-term reduction in body weight have followed subjects for more than 6-12 months. This may be due to the challenging problems concerning overweight individuals in completing and adhering to increased levels of physical activity. In a study conducted by Donnelly and Smith <ref name=five>Donnelly JE, Smith BK (2005) Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences. ''Exercise and sports sciences reviews'' 33:169-74</ref> less than half the number of individuals engaging in physical activity completed the 16 month study despite being compensated.<ref name=two/>
 
Other factors influencing results and energy balance may include compensation mechanisms such as changes in resting metabolic rate (RMR) as well as increased energy intake due to long-term augmented energy expenditure which may attenuate weight loss.<ref name=two/> Difficulties in interpreting results may arise when calculating body weight, as adipose tissue lost due to exercise may be overshadowed by an increase in lean muscle mass. Studies that measure body composition compared to body weight solely, illustrate that exercise “reduces abdominal visceral fat” and “improves cardio metabolic risk factors”.<ref name=two/> Consequently body weight may not be the best measure to evaluate the effects of physical activity on health.
 
The results mentioned above as well as being equivalent to results of Schoeller ''et al.'',<ref name=four/> suggest that appropriate levels of exercise required to sustain weight loss is “approximately twice the public health recommendation,” at least 150 minutes of moderate intensity activity per week.<ref name=three/>
 
===Maintenance of Long-Term Weight Loss===
Many studies have found that, after weight loss, subjects often regain the lost weight, and sometimes even overshoot their original weight.  Abderson ''et al.''analysed a large number and variety of weight loss studies carried out in the USA, and concluded that more than 35% of lost weight is regained within the first year, and most is regained within five years<ref>Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies. ''Am J Clin Nutr'' 74:579-84</ref>. Metabolism plays a key role in this. Among other inputs, the reduced plasma concentrations of [[leptin]] and [[insulin]] that accompany a reduced fat mass tell the brain that the body is energy-deficient, resulting in a drive to eat along with suppressed energy expenditure.  The body’s choice of fuel also changes within the diurnal cycle and is affected by lifestyle.  Therefore, to maintain their new weight, individuals need to limit their food intake to the same extent that expenditure is suppressed.
 
'''The role of exercise'''
 
There is evidence to suggest that regular exercise prevents or counters these metabolic adaptations that lead to weight regain. MacLean ''et al.'' <ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am J Physiol'' 297:793-802</ref> showed that relapsing rats that exercised not only that presented a reduction in weight in liver tissue and mesenteric fat pads compared to their sedentary counterparts, but did not succumb to the overeating normally seen after dramatic weight loss.
 
[NOT CLEAR TO ME WHAT YOU'RE SAYING HERE IN THIS SECTION]
 
The energy balance previously mentioned was delayed and much reduced (roughly 40%), therefore greatly reducing the rats’ desire to gorge themselves.  Lean rats show a diurnal shift in fuel usage (favouring [[carbohydrate]]s during the dark cycle and fat during the light).  Obese rats did not present this shift.  It however returned after weight loss.  (see if can find more on this)  In sedentary rats, carbohydrates were favoured regardless, while fat was stored and increased [[lipogenesis]] was observed. 
 
 
[[AMPK]] is a hypothalamic nutrient sensor (WHAT DO YOU MEAN BY THIS?) that responds to low nutrient availability.  Signals from the periphery (including the hormones leptin and insulin) were not increased by exercise regimes.  The reception of these signals, however, seems to be more involved. Acute bouts of exercise were shown by MacLean ''et al.'' to lessen the response of AMPK to peripheral deprivation signals, thereby reducing the drive to overfeed.<ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am. J Physiol'' 297:793-802</ref> Rats that had lost weight were observed to alternate massive overeating with periods of deprivation. Daily aerobic exercise reduced the extremes in fuel consumption that are associated with this phenomenon as well as the excessive desire to eat and/or hunger pains that are the downfall of many individuals after a calorie-restricted weight loss program.  The authors suggested that preventing the typical increase in [[adipocytes]] may affect the ability to store excess calories, as the peripheries are wired to process and store any fuel excess rapidly and efficiently to promote regain and return to the defended body weight. The drive to physical activity is tightly regulated and directly influences adiposity and body weight.
 
==Contradictory evidence for the link between exercise and a reduction in body weight ==
 
In 2004 it was reported that more than half of British adults are overweight, and that obesity among school children has increased by 70% in the past generation <ref>Jeffery AN ''et al.'' (2004) Parents’ awareness of overweight in themselves and their children: cross sectional study within a cohort (EarlyBird 21). ''BMJ''</ref> The correlation between increasingly sedentary lifestyles and the obesity epidemic has lead to a broad assumption that physical inactivity is to blame for the worldwide crisis. However, there is compelling evidence emerging to the contrary.
 
Perhaps the most reliable reports have been produced by the EarlyBird study, currently underway at the Universities of Exeter and Plymouth. <ref>Metcalf BS ''et al.'' (2001) Technical reliability of the CSA activity monitor: The EarlyBird Study. ''Medicine & Science in Sports & Exercise'' 1533-7</ref> This 12 year cohort study, to be completed in 2013, involves measuring the physical activity and body composition of 300 children from the age of 5. Unlike other trials, physical activity was measured using an impressively precise CSA accelerometer-based activity monitor. Similar previous trials have depended on unreliable qualitative reports from parents or children  One of their 56 peer reviewed articles finds no association between physical activity and BMI or body fat in either sex <ref>Metcalf BS ''et al.'' (2008) Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37) ''Arch Dis Child'' 93: 772-7</ref>.
 
Increasing evidence suggests that children are intrinsically programmed to undertake a set level of activity per day, which is determined either genetically, or as a result of an early childhood experience. Hence, it would be incorrect to implicate TV watching in any resulting daily energy surplus <ref>(Sonneville ''et al.'' (2008)</ref>. Adding further credence to this, results being published by EarlyBird in the near future suggest that it is obesity that makes children decreasingly active, and not inactivity that makes children obese.
 
A cluster randomised controlled trial was carried out in Glasgow, in which 545 pre-school children were subjected to a realistic level of enhanced activity per week, over 24 weeks. It was similarly deduced from this study that physical activity does not reduce BMI in young children <ref>Reilly JJ ''et al.''(2006) Physical activity to prevent obesity in young children: cluster randomised controlled trial. ''BMJ'' </ref>. The same conclusion was reached  by Harris ''et al.'' who scrutinised 18 studies meeting inclusion criteria to explore the effect of school-based physical activity interventions on BMI in children. <ref>Harris ''et al.'' (2009)</ref>
 
Such findings have not been exclusive to children. Church randomized 411 sedentary women to either 1 of 3 exercise groups of varying energy expenditure, or a non-exercise control group. He found that the group assigned to no exercise lost a similar amount of weight to the exercisers <ref>Church ''et al.'' (2009) Changes in weight, waist circumference and compensatory responses with different doses of exercise among sedendary, overweight postmenopausal women. ''PLoS ONE'' 4 (2):1-11.</ref>.
The explanation for this controversial evidence may depend on the observation that exercise increases appetite through orexigenic peptides such as NPY <ref>Lewis ''et al.'' (1993)</ref>. Caloric overcompensation is the result of our limited capacity to deal with excess calories, due to our minimal brown fat stores, the activation of orexigenic and reward pathways in the brain, and the tendency to underestimate calorie consumption. The frequent result is excessive dietary intake, resulting in an energy imbalance and net weight gain. This theory is supported by an 18-month study by Sonneville and Gortmaker involving 538 students who, on average, consumed 100 calories more than they had just expended following exercise <ref> Sonneville KR, Gortmaker SL (2008) Total energy intake, adolescent discretionary behaviours and the energy gap. ''Int J Obesity'' 32:19-27</ref>.
 
Although the link between exercise and weight loss is tenuous, one must not underestimate the potential benefits of exercise in not only preventing numerous diseases, but also in enhancing mental health and cognitive ability.
 
These findings suggest that, in the absence of the will-power to override the desire to consume surplus calories post exercise, the key to achieving a net daily energy deficit is not to increase exercise, but to limit daily calorie consumption.
 
== '''Conclusion''' ==
There is a lot of contradictory evidence presented. For instance, if we are to look at the maintenance of a reduced body weight, we find plenty of arguments for and against exercise having a positive effect, not least due to the fact that the time period over which these studies were conducted ranged from 6 months to 3 years, whereas body weight has been shown to fluctuate up to 5 years after weight loss.  Parallel to this are the problems that obese subjects may encounter in adhering to an exercise program due to the inherent limitations of their condition.  Papers tend to concentrate on obese individuals, which does raise questions about the relevance of their statistics.   
 
It should be noted, however, that in many cases, results are seen, especially when counseling, group sessions, and interventions are included in the program.  Although it is not activity but resting metabolism that makes up the greatest energy expenditure within the body, it seems that exercise does indeed play a very important role in both preventing, reaching and defending a lower body weight.
 
==References==
<references/>
 
http://www.earlybirddiabetes.org
 
The Times. ‘Exercise? A fat lot of good that is if you want to lose weight’. ''Times'' October 19th 2009.
 
Harris KC ''et al.''(2009) Effect of school-based physical activity interventions on body mass index in children: a meta-analysis. ''Can Med Ass J'' 180:719-26.
 
 
Lewis DE ''et al.'' (1993) Intense exercise and food restriction cause similar hypothalamic neuropeptide Y increases in rats. ''Ame J Physiol'' 264:279-84.
 
Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies  ''Am J Clin Nutrition''. 74:579-84.
 
==The Effect of exercise on the production and maintenance of long-term reduction in body weight ==
 
===Exercise intensity and duration on long-term weight loss===
 
Increased levels of physical activity can be effective in reducing body weight, but the optimal amount of exercise that will facilitate a long-term reduction in body weight is still unclear. Recent [[randomized, controlled trials]] (RCTs) demonstrate slight weight loss with physical activity intervention alone and little increase in weight loss combining exercise and dietary restriction.<ref name=two/> Topical studies show that higher levels of exercise may result in greater weight loss.<ref name=three/>
 
Most recent studies show that a reduction in body weight of 1-3kg can be achieved over 4-16 months using exercise prescriptions of 60-180 min per week.<ref name=two/> Jakicic ''et al.'' as well as other study groups, are interested in the effect of increased intensity (moderate vs vigorous) and duration (moderate vs. high) of exercise on long-term weight loss.<ref name=three/>,<ref name=four>Schoeller DA, Shay K, Kushner RF (1997) How much physical activity is needed to minimize weight gain in previously obese women? ''Am J Clin Nutr'' 66:551-6</ref> Individuals achieving and sustaining a weight loss of 10% or more of their initial body weight after 24 months carried out more physical activity than those who maintained a weight loss of less than 10%.<ref name=three/> This study demonstrates a correlation between increased leisure time activity and weight loss over time, concluding that 275 min/week (1500 kcal/week) is needed to sustain weight loss. This suggests that increased exercise intensity and duration may create a large negative energy balance resulting in substantial weight loss.
 
However, few studies of the amount and intensity of exercise required to augment long-term reduction in body weight have followed subjects for more than 6-12 months. This may be due to the challenging problems concerning overweight individuals in completing and adhering to increased levels of physical activity. In a study conducted by Donnelly and Smith <ref name=five>Donnelly JE, Smith BK (2005) Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences. ''Exercise and sports sciences reviews'' 33:169-74</ref> less than half the number of individuals engaging in physical activity completed the 16 month study despite being compensated.<ref name=two/>
 
Other factors influencing results and energy balance may include compensation mechanisms such as changes in resting metabolic rate (RMR) as well as increased energy intake due to long-term augmented energy expenditure which may attenuate weight loss.<ref name=two/> Difficulties in interpreting results may arise when calculating body weight, as adipose tissue lost due to exercise may be overshadowed by an increase in lean muscle mass. Studies that measure body composition compared to body weight solely, illustrate that exercise “reduces abdominal visceral fat” and “improves cardio metabolic risk factors”.<ref name=two/> Consequently body weight may not be the best measure to evaluate the effects of physical activity on health.
 
The results mentioned above as well as being equivalent to results of Schoeller ''et al.'',<ref name=four/> suggest that appropriate levels of exercise required to sustain weight loss is “approximately twice the public health recommendation,” at least 150 minutes of moderate intensity activity per week.<ref name=three/>
 
===Maintenance of Long-Term Weight Loss===
Many studies have found that, after weight loss, subjects often regain the lost weight, and sometimes even overshoot their original weight.  Abderson ''et al.''analysed a large number and variety of weight loss studies carried out in the USA, and concluded that more than 35% of lost weight is regained within the first year, and most is regained within five years<ref>Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies. ''Am J Clin Nutr'' 74:579-84</ref>. Metabolism plays a key role in this. Among other inputs, the reduced plasma concentrations of [[leptin]] and [[insulin]] that accompany a reduced fat mass tell the brain that the body is energy-deficient, resulting in a drive to eat along with suppressed energy expenditure.  The body’s choice of fuel also changes within the diurnal cycle and is affected by lifestyle.  Therefore, to maintain their new weight, individuals need to limit their food intake to the same extent that expenditure is suppressed.
 
'''The role of exercise'''
 
There is evidence to suggest that regular exercise prevents or counters these metabolic adaptations that lead to weight regain. MacLean ''et al.'' <ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am J Physiol'' 297:793-802</ref> showed that relapsing rats that exercised not only that presented a reduction in weight in liver tissue and mesenteric fat pads compared to their sedentary counterparts, but did not succumb to the overeating normally seen after dramatic weight loss.
 
[NOT CLEAR TO ME WHAT YOU'RE SAYING HERE IN THIS SECTION]
 
The energy balance previously mentioned was delayed and much reduced (roughly 40%), therefore greatly reducing the rats’ desire to gorge themselves.  Lean rats show a diurnal shift in fuel usage (favouring [[carbohydrate]]s during the dark cycle and fat during the light).  Obese rats did not present this shift.  It however returned after weight loss.  (see if can find more on this)  In sedentary rats, carbohydrates were favoured regardless, while fat was stored and increased [[lipogenesis]] was observed. 
 
 
[[AMPK]] is a hypothalamic nutrient sensor (WHAT DO YOU MEAN BY THIS?) that responds to low nutrient availability.  Signals from the periphery (including the hormones leptin and insulin) were not increased by exercise regimes.  The reception of these signals, however, seems to be more involved. Acute bouts of exercise were shown by MacLean ''et al.'' to lessen the response of AMPK to peripheral deprivation signals, thereby reducing the drive to overfeed.<ref>MacLean PS ''et al.''(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. ''Am. J Physiol'' 297:793-802</ref> Rats that had lost weight were observed to alternate massive overeating with periods of deprivation. Daily aerobic exercise reduced the extremes in fuel consumption that are associated with this phenomenon as well as the excessive desire to eat and/or hunger pains that are the downfall of many individuals after a calorie-restricted weight loss program.  The authors suggested that preventing the typical increase in [[adipocytes]] may affect the ability to store excess calories, as the peripheries are wired to process and store any fuel excess rapidly and efficiently to promote regain and return to the defended body weight. The drive to physical activity is tightly regulated and directly influences adiposity and body weight.
 
==Contradictory evidence for the link between exercise and a reduction in body weight ==
 
In 2004 it was reported that more than half of British adults are overweight, and that obesity among school children has increased by 70% in the past generation <ref>Jeffery AN ''et al.'' (2004) Parents’ awareness of overweight in themselves and their children: cross sectional study within a cohort (EarlyBird 21). ''BMJ''</ref> The correlation between increasingly sedentary lifestyles and the obesity epidemic has lead to a broad assumption that physical inactivity is to blame for the worldwide crisis. However, there is compelling evidence emerging to the contrary.
 
Perhaps the most reliable reports have been produced by the EarlyBird study, currently underway at the Universities of Exeter and Plymouth. <ref>Metcalf BS ''et al.'' (2001) Technical reliability of the CSA activity monitor: The EarlyBird Study. ''Medicine & Science in Sports & Exercise'' 1533-7</ref> This 12 year cohort study, to be completed in 2013, involves measuring the physical activity and body composition of 300 children from the age of 5. Unlike other trials, physical activity was measured using an impressively precise CSA accelerometer-based activity monitor. Similar previous trials have depended on unreliable qualitative reports from parents or children  One of their 56 peer reviewed articles finds no association between physical activity and BMI or body fat in either sex <ref>Metcalf BS ''et al.'' (2008) Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37) ''Arch Dis Child'' 93: 772-7</ref>.
 
Increasing evidence suggests that children are intrinsically programmed to undertake a set level of activity per day, which is determined either genetically, or as a result of an early childhood experience. Hence, it would be incorrect to implicate TV watching in any resulting daily energy surplus <ref>(Sonneville ''et al.'' (2008)</ref>. Adding further credence to this, results being published by EarlyBird in the near future suggest that it is obesity that makes children decreasingly active, and not inactivity that makes children obese.
 
A cluster randomised controlled trial was carried out in Glasgow, in which 545 pre-school children were subjected to a realistic level of enhanced activity per week, over 24 weeks. It was similarly deduced from this study that physical activity does not reduce BMI in young children <ref>Reilly JJ ''et al.''(2006) Physical activity to prevent obesity in young children: cluster randomised controlled trial. ''BMJ'' </ref>. The same conclusion was reached  by Harris ''et al.'' who scrutinised 18 studies meeting inclusion criteria to explore the effect of school-based physical activity interventions on BMI in children. <ref>Harris ''et al.'' (2009)</ref>
 
Such findings have not been exclusive to children. Church randomized 411 sedentary women to either 1 of 3 exercise groups of varying energy expenditure, or a non-exercise control group. He found that the group assigned to no exercise lost a similar amount of weight to the exercisers <ref>Church ''et al.'' (2009) Changes in weight, waist circumference and compensatory responses with different doses of exercise among sedendary, overweight postmenopausal women. ''PLoS ONE'' 4 (2):1-11.</ref>.
The explanation for this controversial evidence may depend on the observation that exercise increases appetite through orexigenic peptides such as NPY <ref>Lewis ''et al.'' (1993)</ref>. Caloric overcompensation is the result of our limited capacity to deal with excess calories, due to our minimal brown fat stores, the activation of orexigenic and reward pathways in the brain, and the tendency to underestimate calorie consumption. The frequent result is excessive dietary intake, resulting in an energy imbalance and net weight gain. This theory is supported by an 18-month study by Sonneville and Gortmaker involving 538 students who, on average, consumed 100 calories more than they had just expended following exercise <ref> Sonneville KR, Gortmaker SL (2008) Total energy intake, adolescent discretionary behaviours and the energy gap. ''Int J Obesity'' 32:19-27</ref>.
 
Although the link between exercise and weight loss is tenuous, one must not underestimate the potential benefits of exercise in not only preventing numerous diseases, but also in enhancing mental health and cognitive ability.
 
These findings suggest that, in the absence of the will-power to override the desire to consume surplus calories post exercise, the key to achieving a net daily energy deficit is not to increase exercise, but to limit daily calorie consumption.
 
== '''Conclusion''' ==
There is a lot of contradictory evidence presented. For instance, if we are to look at the maintenance of a reduced body weight, we find plenty of arguments for and against exercise having a positive effect, not least due to the fact that the time period over which these studies were conducted ranged from 6 months to 3 years, whereas body weight has been shown to fluctuate up to 5 years after weight loss.  Parallel to this are the problems that obese subjects may encounter in adhering to an exercise program due to the inherent limitations of their condition.  Papers tend to concentrate on obese individuals, which does raise questions about the relevance of their statistics.   
 
It should be noted, however, that in many cases, results are seen, especially when counseling, group sessions, and interventions are included in the program.  Although it is not activity but resting metabolism that makes up the greatest energy expenditure within the body, it seems that exercise does indeed play a very important role in both preventing, reaching and defending a lower body weight.
 
==References==
<references/>
 
http://www.earlybirddiabetes.org
 
The Times. ‘Exercise? A fat lot of good that is if you want to lose weight’. ''Times'' October 19th 2009.
 
Harris KC ''et al.''(2009) Effect of school-based physical activity interventions on body mass index in children: a meta-analysis. ''Can Med Ass J'' 180:719-26.
 
 
Lewis DE ''et al.'' (1993) Intense exercise and food restriction cause similar hypothalamic neuropeptide Y increases in rats. ''Ame J Physiol'' 264:279-84.
 
Anderson JW ''et al.'' (2001) Long-term weight-loss maintenance: a meta-analysis of US studies  ''Am J Clin Nutrition''. 74:579-84.

Latest revision as of 16:00, 14 August 2024

This article is developed but not approved.
 Main Article
 Discussion
Related Articles  [?]
Bibliography  [?]
External Links  [?]
Citable Version  [?]
 
https://en.citizendium.org/wiki/index.php?title=Exercise_and_body_weight&printable=yes
This editable, developed Main Article is subject to a disclaimer.

Exercise and body weight refers to the evidence that exercise is linked to a long-term reduction in body weight, and the controversy involved.

Figure 1.jpg

Excessive adiposity now affects more than one billion people worldwide.[1] Adipose tissue is essential for energy use and heat production, but individuals with excess adiposity are at risk of serious co-morbidities including type II diabetes, hypertension and cardiovascular diseases and many more.[1] [2]

Excessive adiposity results from an imbalance in energy homeostasis. Energy balance is the difference between energy expenditure and energy intake; a negative energy balance will mean that body weight is lost over time, while a positive energy balance means that weight will be gained.[2] The brain is constantly readjusting metabolic rate and behavior to maintain a target weight (the "set point"; the level of body weight below which the brain triggers mechanisms to conserve energy stores, and above which the brain triggers mechanisms to consume energy). Diet and exercise may alter this set point, but only very slowly; metabolic adaptations to 'defend' the set point mean that it can be very difficult to maintain weight loss that has been achieved by an acute diet or by exercise.

There is controversy regarding the amount of physical activity necessary to facilitate weight loss maintenance. This article explores this debate and puts forward results supporting and opposing the positive relationship between exercise and body weight.[2][3]

The effect of exercise on the production and maintenance of long-term reduction in body weight

A meta-analysis of randomized controlled trials by the international Cochrane Collaboration found that "exercise combined with diet resulted in a greater weight reduction than diet alone".[4] Use of a pedometer may assist in exercising for weight loss.[5]

Exercise intensity and duration

Increased physical activity can be effective in reducing body weight, but the optimal amount of exercise that will facilitate a long-term reduction in body weight is still unclear. Recent randomized controlled trials (RCTs) show only slight weight loss with physical activity intervention alone and little increase in weight loss combining exercise and dietary restriction.[2] Some studies show that higher levels of exercise may result in greater weight loss.[3]

Most recent studies show that a reduction in body weight of 1-3kg can be achieved over 4-16 months using exercise prescriptions of 60-180 min per week.[2] [3],[6] Individuals achieving and sustaining a weight loss of 10% or more of their initial body weight after 24 months carried out more physical activity than those who maintained a weight loss of less than 10%.[3]

However, few studies of the amount of exercise required to augment long-term reduction in body weight have followed subjects for more than 6-12 months. This may be due to the challenging problems concerning overweight individuals in completing and adhering to increased levels of physical activity. In one study, [7] fewer than half the number of individuals engaging in physical activity completed the 16 month study despite being compensated for taking part.

Other factors influencing results include compensation mechanisms such as changes in resting metabolic rate as well as increased energy intake.[2] Moreover, difficulties in interpreting results may arise when calculating body weight, as adipose tissue lost due to exercise may be overshadowed by an increase in lean muscle mass. Studies that measure body composition compared to body weight solely, illustrate that exercise “reduces abdominal visceral fat” and “improves cardio metabolic risk factors”.[2] Consequently body weight may not be the best measure to evaluate the effects of physical activity on health. These results, and those of Schoeller et al.,[6] suggest that the level of exercise required to sustain weight loss is “approximately twice the public health recommendation,” - at least 150 minutes of moderate intensity activity each week.[3]

Maintenance of long-term weight loss

After weight loss, subjects often regain the lost weight, and sometimes even overshoot their original weight. Abderson et al. analysed a large number and variety of weight loss studies carried out in the USA, and concluded that more than 35% of lost weight is regained within the first year, and most is regained within five years.[8] Among other inputs, the reduced plasma concentrations of leptin and insulin that accompany a reduced fat mass result in an increased drive to eat along with suppressed energy expenditure. The body’s choice of fuel also changes within the diurnal cycle and is affected by lifestyle. Therefore, to maintain their new weight, individuals need to limit their food intake to the same extent that expenditure is suppressed.

Regular exercise may prevent or counter these metabolic adaptations that can lead to weight regain. MacLean et al. [9] showed that relapsing rats that exercised not only lost weight in liver and mesenteric fat pads compared to sedentary counterparts, but did not succumb to the overeating normally seen after dramatic weight loss. The energy balance previously mentioned was delayed and much reduced (roughly 40%), therefore greatly reducing the rats’ desire to gorge themselves. Lean rats show a diurnal shift in fuel usage (favouring carbohydrates during the dark phase and fat during the light phase). Obese rats did not present this shift. In sedentary rats, carbohydrates were favoured regardless, while fat was stored and increased lipogenesis was observed.

AMPK is a hypothalamic nutrient sensor that responds to low nutrient availability. Signals from the periphery (including the hormones leptin and insulin) were not increased by exercise regimes, but acute bouts of exercise lessen the response of AMPK to peripheral deprivation signals, thereby reducing the drive to overfeed.[10] Rats that had lost weight were observed to alternate massive overeating with periods of deprivation. Daily aerobic exercise reduced the extremes in fuel consumption that are associated with this phenomenon as well as the excessive desire to eat and/or hunger pains that are the downfall of many individuals after calorie-restricted weight loss. Preventing the typical increase in adipocytes may affect the ability to store excess calories, as the peripheries are wired to process and store any fuel excess rapidly and efficiently to promote regain and return to the defended body weight.

Contradictory evidence for the link between exercise and a reduction in body weight

In 2004, it was reported that more than half of British adults are overweight, and that obesity among school children has increased by 70% in the past generation [11] The correlation between increasingly sedentary lifestyles and the obesity epidemic has lead to a broad assumption that physical inactivity is to blame for the worldwide crisis. However, there is compelling evidence emerging to the contrary.

Perhaps the most reliable reports have been produced by the "EarlyBird" study at the Universities of Exeter and Plymouth.[12] This 12 year cohort study, to be completed in 2013, involves measuring the physical activity and body composition of 300 children from the age of 5. Unlike other trials, physical activity was measured using an impressively precise CSA accelerometer-based activity monitor. Similar previous trials have depended on unreliable qualitative reports from parents or children. One of their 56 peer reviewed articles finds no association between physical activity and BMI or body fat in either sex. [13]

Increasing evidence suggests that children are intrinsically programmed to undertake a set level of activity per day, which is determined either genetically, or as a result of early childhood experience. Hence, it would be incorrect to implicate TV watching in any resulting daily energy surplus [14]. Adding further credence to this, recent results of EarlyBird suggest that it is obesity that makes children decreasingly active, and not inactivity that makes children obese.

A cluster randomised controlled trial was carried out in Glasgow, in which 545 pre-school children were subjected to a realistic level of enhanced activity per week, over 24 weeks. It was similarly deduced from this study that physical activity does not reduce BMI in young children [15]. The same conclusion was reached by Harris et al., who scrutinised 18 studies meeting inclusion criteria to explore the effect of school-based physical activity interventions on BMI in children. [16]

Such findings have not been exclusive to children. Church randomized 411 sedentary women to either 1 of 3 exercise groups of varying energy expenditure, or a non-exercise control group. He found that the group assigned to no exercise lost a similar amount of weight to the exercisers [17]

The explanation may depend on the observation that exercise increases appetite through orexigenic peptides such as NPY [18]. Caloric overcompensation is the result of our limited capacity to deal with excess calories, due to our minimal brown fat stores, the activation of orexigenic and reward pathways in the brain, and the tendency to underestimate calorie consumption. The frequent result is excessive dietary intake, resulting in an energy imbalance and net weight gain. This theory is supported by an 18-month study by Sonneville and Gortmaker involving 538 students who, on average, consumed 100 calories more than they had just expended following exercise [19].

These findings suggest that, in the absence of the will-power to override the desire to consume surplus calories post exercise, the key to achieving a net daily energy deficit is not to increase exercise, but to limit daily calorie consumption.

References

  1. ↑ 1.0 1.1 Redinger RN (2009) Fat storage and the biology of energy expenditure Translational Research: J Lab Clin Med 154:52-60
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Catenacci VA, Wyatt HR (2007) The role of physical activity in producing and maintaining weight loss. Nat Clin Pract Endocrinol Metabol 3:518-29
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Jakicic JM et al.(2008) Effect of exercise on 24-month weight loss maintenance in overweight women Arch Int Med 168:1550-9
  4. ↑ Shaw K et al. (2006). "Exercise for overweight or obesity". Cochrane database of systematic reviews (Online): CD003817. DOI:10.1002/14651858.CD003817.pub3. PMID 17054187. Research Blogging.
  5. ↑ Richardson CR et al. (2008). "A meta-analysis of pedometer-based walking interventions and weight loss". Ann Fam Med: 69–77. DOI:10.1370/afm.761. PMID 18195317. Research Blogging.
  6. ↑ 6.0 6.1 Schoeller DA et al. (1997) How much physical activity is needed to minimize weight gain in previously obese women? Am J Clin Nutr 66:551-6
  7. ↑ Donnelly JE, Smith BK (2005) Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences Exercise Sports Sci Rev 33:169-74
  8. ↑ Anderson JW et al. (2001) Long-term weight-loss maintenance: a meta-analysis of US studies Am J Clin Nutr 74:579-84
  9. ↑ MacLean PS et al.(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. Am J Physiol 297:793-802
  10. ↑ MacLean PS et al.(2009) Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss Am J Physiol 297:793-802
  11. ↑ Jeffery AN et al. (2004) Parents’ awareness of overweight in themselves and their children: cross sectional study within a cohort (EarlyBird 21) BMJ
  12. ↑ Metcalf BS et al. (2001) Technical reliability of the CSA activity monitor: The EarlyBird Study. Medicine & Science in Sports & Exercise 1533-7
  13. ↑ Metcalf BS et al. (2008) Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37) Arch Dis Child 93:772-7
  14. ↑ (Sonneville et al. (2008)
  15. ↑ Reilly JJ et al.(2006) Physical activity to prevent obesity in young children: cluster randomised controlled trial BMJ
  16. ↑ Harris et al. (2009)
  17. ↑ Church et al. (2009) Changes in weight, waist circumference and compensatory responses with different doses of exercise among sedendary, overweight postmenopausal women. PLoS ONE 4:1-11
  18. ↑ Lewis et al. (1993)
  19. ↑ Sonneville KR, Gortmaker SL (2008) Total energy intake, adolescent discretionary behaviours and the energy gap. Int J Obesity 32:19-27
Retrieved from "https://citizendium.org/wiki/index.php?title=Exercise_and_body_weight&oldid=971594"