Obesity

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Causes/etiology

Obesity is caused by a mix of environmental and genetic factors.[1][2] In only very few cases can obesity in humans be attributed to a single gene defect, but many genes have been found that have variants associated with an increased risk of obesity. One of the few genes that variants in the human population associated with increased risk of obesity is the gene for the melanocortin 4 receptor (MC4R). This receptor is expressed in the hypothalamus, and mediates the actions of alpha melanocyte stimulating hormone, a peptide released by a subpopulation of neurons in the arcuate nucleus in response to leptin. [3] (see Hunger for more information).

The secular increase in overweight and obesity (the increase that has taken place during the XXth century and is continuing today) is most obviously due to environmental changes (in the widest sense), the most commonly discussed obesogenic factors being diet and exercise ("The Big Two").

This is not to say that no relevant obesogenic changes in the Human genetic pool happened during this period, and this does not exclude epigenetic modifications of the genome. In a multi-center review of the literature on the possible causes of this secular trend, 10 other factors, including epigenetic changes and modifications in mating behaviours modulating the gene pool, were found to be equally plausible etiologic factors contributing to the epidemic.[4] This analysis, published in the International Journal of Obesity, found "evidence (in favor of the following factors was) in many cases (...) as compelling as the evidence for more commonly discussed putative explanations (diet and physical activity)":

  1. Sleep debt
  2. Endocrine disruptors (man made chemicals interfering with any possible step of hormone signalling; in particular, disruptors of sex hormones)
  3. Reduction in variability in ambient temperature (increase time spent in thermoneutral areas)
  4. Decreased smoking
  5. Pharmaceutical iatrogenesis (drug-induced weight gain: many modern drugs widely used today cause weight gain)
  6. Changes in distribution of ethnicity and age (some age and ethnic groups where obesity is more common have grown in number)
  7. Increasing gravida age (giving birth at an older age, which is a worlwide trend, is a risk factor for obesity in the offspring)
  8. Intrauterine and intergenerational effects (trends in obesity incidence may reflect (probably epigenetic) changes that occured a generation or more before)
  9. High BMI leads to reproductive fitness (reproducing at a higher rate)
  10. Assortative mating and floor effects (a tendency to search for mates with comparable phenotypes (physical appearance), coupled to a floor effect (a loss of reproductive fitness with increasing leanness), leading, over time, in a snowball effect to epidemic proportions of overweight)

These explanations neither compete with each other, nor with the "Big Two", but call into question the significance of interventions and researches that are focussing solely on caloric intake and expenditure (diet and exercise).

Treatment

The mainstay of treatment for obesity is an energy-limited diet and increased exercise. In studies, diet and exercise programs have consistently produced an average weight loss of approximately 8% of total body mass (excluding study drop-outs). While not all dieters will be satisfied with this outcome, studies have shown that a loss of as little as 5% of body mass can create large health benefits. A more intractable therapeutic problem appears to be weight loss maintenance. Of dieters who manage to lose 10% or more of their body mass in studies, 80-95% will regain that weight within two to five years, supporting the finding that the body has various mechanisms that maintain weight at a certain set point.

In a clinical practice guideline by the American College of Physicians, the following five recommendations are made:[5]

  1. People with a BMI of over 30 should be counseled on diet, exercise and other relevant behavioral interventions, and set a realistic goal for weight loss.
  2. If these goals are not achieved, pharmacotherapy can be offered. The patient needs to be informed of the possibility of side-effects and the unavailability of long-term safety and efficacy data.
  3. Drug therapy may consist of sibutramine, orlistat, phentermine, diethylpropion, fluoxetine, and bupropion. For more severe cases of obesity, stronger drugs such as amphetamine and methamphetamine may be used on a selective basis. Evidence is not sufficient to recommend sertraline, topiramate, or zonisamide.
  4. In patients with BMI > 40 who fail to achieve their weight loss goals (with or without medication) and who develop obesity-related complications, referral for bariatric surgery may be indicated. The patient needs to be aware of the potential complications.
  5. Those requiring bariatric surgery should be referred to high-volume referral centers, as the evidence suggests that surgeons who frequently perform these procedures have fewer complications.

A clinical practice guideline by the US Preventive Services Task Force (USPSTF) concluded that the evidence is insufficient to recommend for or against routine behavioral counseling to promote a healthy diet in unselected patients in primary care settings, but that intensive behavioral dietary counseling is recommended in those with hyperlipidemia and other known risk factors for cardiovascular and diet-related chronic disease. Intensive counseling can be delivered by primary care clinicians or by referral to other specialists, such as nutritionists or dietitians.[6][7]

Counseling

A meta-analysis of randomized controlled trials concluded that "compared with usual care, dietary counseling interventions produce modest weight losses that diminish over time."[8]

The role of genetic counseling is unclear[9]; however, based on a study done of hypercholesterolemia, it is possible that genetic counseling might lead to patients preferring medication over diet therapy.[10]

Portion control plate

A randomized controlled trial found that patients using portion control plates and log books had more weight loss and less use of hypoglycemic drugs.[11]

Internet-based counseling

The Internet offer a method to increase patient participation in their health care. A randomized controlled trial showed some benefit in a weight loss program that used the Internet.[12]

Diets

Various dietary approaches have been proposed, some of which have been compared by randomized controlled trials:

"all 4 diets resulted in modest statistically significant weight loss at 1 year, with no statistically significant differences between diets"
"The higher discontinuation rates for the Atkins and Ornish diet groups suggest many individuals found these diets to be too extreme"

Low carbohydrate versus low fat diets

Many studies have focused on diets that reduce calories via a low-carbohydrate (Atkins diet, Zone diet) diet versus a low-fat diet (LEARN diet, Ornish diet). The Nurses' Health Study, an observational cohort study, found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less coronary heart disease.[15]

A meta-analysis of randomized controlled trials by the Cochrane Collaboration in 2002 concluded[16] that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people.

A more recent meta-analysis that included randomized controlled trials published after the Cochrane review[17][18][14] found that "low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered."[19]

The Women's Health Initiative Randomized Controlled Dietary Modification Trial[20] found that a diet of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily:

  • no reduction in cardiovascular disease[21]
  • an insignificant reduction in invasive breast cancer[22]
  • no reductions in colorectal cancer[23]

Additional recent randomized controlled trials have found that:

  • The choice of diet for a specific person may be influenced by measuring the invididual's insulin secretion:
In young adults "Reducing glycemic [carbohydrate] load may be especially important to achieve weight loss among individuals with high insulin secretion."[25] This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.[26][27]

Low glycemic index

"The glycaemic index factor is a ranking of foods based on their overall effect on blood sugar levels. Low glycaemic index foods, such as lentils, provide a slower more consistent source of glucose to the bloodstream, thereby stimulating less insulin release than high glycaemic index foods, such as white bread."[28][29]

The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".[30]

In a randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results[31]:

  • Diet 1 and 2 were high carbohydrate (55% of total energy intake)
    • Diet 1 was high-glycemic index
    • Diet 2 was low-glycemic index
  • Diet 3 and 4 were high protein (25% of total energy intake)
    • Diet 3 was high-glycemic index
    • Diet 4 was low-glycemic index

Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3. Thus the authors concluded that the high-carbohydrate, low-glycemic index diet was the most favorable.

A meta-analysis by the Cochrane Collaboration concluded that low glycemic index or low glycemic load diets led to more weight loss and better lipid profiles. However, the Cochrane Collaboration grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index.[28]

Exercise

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".[32]

Use of a pedometer may assist in exercising for weight loss.[33]

Drugs

A systematic review found that the average weight loss after at least one year was:[34]

  • Orlistat: 2.9 kg, but produced gastrointestinal side effects.
  • Sibutramine: 4.2 kg, but raised blood pressure and pulse.
  • Rimonabant: 4.7-kg, but associated with increased psychiatric disorders. About a third of patients discontinued treatment.[35][34]

For patients with diabetes mellitus type 2, metformin (Glucophage) can assist in weight loss—rather than sulfonylurea derivatives and insulin, which often lead to further weight gain. The thiazolidinediones (rosiglitazone or pioglitazone) can cause slight weight gain, but decrease the "pathologic" form of abdominal fat, and so may help obese diabetics.

Bariatric surgery

Bariatric surgery (or "weight loss surgery") is the use of surgical interventions in the treatment of obesity. As every surgical intervention may lead to complications, it is regarded as a last resort when dietary modification and pharmacological treatment have proven to be unsuccessful.

Types of surgery

Weight loss surgery relies on various principles. Band surgery is reversible, while bowel shortening operations are not. Some procedures can be performed laparoscopically.

  • Predominantly malabsorptive procedures Others procedures also reduce the length of bowel that food will be in contact with, directly reducing absorption (gastric bypass surgery).

Complications

Complications from weight loss surgery are frequent.[36] The reduction in intestinal absorptive capacity may cause, for instance, persistent anemia only reversible though the intravenous route.[37]

Effectiveness of surgery

Weight loss

In general, the malabsorptive procedures lead to more weight loss than the restrictive procedures. A meta-analysis by the American College of Physicians reports the following weight loss at 36 months:[38]

  • Biliopancreatic diversion - 53 kg
  • Roux-en-Y gastric bypass (RYGB) - 41 kg
    • Open - 42 kg
    • Laparoscopic - 38 kg
  • Adjustable gastric banding - 35 kg
  • Vertical banded gastroplasty - 32 kg
Mortality

Two studies report decrease in mortality from bariatric surgery.[39][40] In the Swedish randomized controlled trial, patients with a body mass index of 34 or more for men and 38 or more for women underwent various types of bariatric surgery and were followed for a mean of 11 years. Surgery patients had 5.0% mortality while control patients had 6.3% mortality. This means 75 patients must be treated to avoid one death after 11 years (number needed to treat is 77).[39] In a Utah retrospective cohort study that followed patients for a mean of 7 years after various types of gastric bypass, surgery patients had 0.4% mortality while control patients had 0.6% mortality.[40]

Remission of diabetes

Bariatric surgery remits diabetes mellitus type 2 in more than 1 of every two people after 2 years if they are similar to the patients in the randomized controlled trial / meta-analysis by Dixon et al. (Number needed to treat is 1.7).[41] In this trial 73% of the patients who remitted their diabetes versus 13% of the patients in the control group.

Prevention

Display of calorie information on the menus or menu boards of restaurants has been proposed by the city of New York.[42]

Eating breakfast may reduce weight gain by adolescents[43]

References

  1. ↑ Stunkard AJ et al. (1990). "The body-mass index of twins who have been reared apart". N. Engl. J. Med. 322 (21): 1483–7. PMID 2336075. [e]
  2. ↑ Christakis NA, Fowler JH (2007). "The spread of obesity in a large social network over 32 years". N Engl J Med 357: 370–9. DOI:10.1056/NEJMsa066082. PMID 17652652. Research Blogging.
  3. ↑ Farooqi IS et al. (2003). "Clinical spectrum of obesity and mutations in the melanocortin 4 receptor gene". N Engl J Med 348 (12): 1085–95. DOI:10.1056/NEJMoa022050. PMID 12646665. Research Blogging.
  4. ↑ Keith SW, Redden DT, Katzmarzyk PT, et al (November 2006). "Putative contributors to the secular increase in obesity: exploring the roads less traveled". Int J Obes (Lond) 30 (11): 1585–94. PMID 16801930.
  5. ↑ Snow V, Barry P, Fitterman N, Qaseem A, Weiss K (2005). "Pharmacologic and surgical management of obesity in primary care: a clinical practice guideline from the American College of Physicians". Ann Intern Med 142 (7): 525-31. PMID 15809464. Fulltext.
  6. ↑ Behavioral counseling in primary care to promote a healthy diet: recommendations and rationale.. Retrieved on 2007-05-22.
  7. ↑ Pignone MP, Ammerman A, Fernandez L, et al (2003). "Counseling to promote a healthy diet in adults: a summary of the evidence for the U.S. Preventive Services Task Force". American journal of preventive medicine 24 (1): 75-92. PMID 12554027. [e]
  8. ↑ Dansinger ML, Tatsioni A, Wong JB, Chung M, Balk EM (2007). "Meta-analysis: the effect of dietary counseling for weight loss". Ann. Intern. Med. 147 (1): 41-50. PMID 17606960. [e]
  9. ↑ Marteau T et al. (2004). "Psychological impact of genetic testing for familial hypercholesterolemia within a previously aware population: a randomized controlled trial". Am. J. Med. Genet. A 128: 285–93. DOI:10.1002/ajmg.a.30102. PMID 15216550. Research Blogging.
  10. ↑ Rief W et al. (2007). "Is information on genetic determinants of obesity helpful or harmful for obese people?--A randomized clinical trial". J Gen Intern Med 22: 1553–9. DOI:10.1007/s11606-007-0353-7. PMID 17879121. Research Blogging.
  11. ↑ Pedersen SD, Kang J, Kline GA (2007). "Portion control plate for weight loss in obese patients with type 2 diabetes mellitus: a controlled clinical trial". Arch. Intern. Med. 167: 1277–83. DOI:10.1001/archinte.167.12.1277. PMID 17592101. Research Blogging. ACP Journal Club review
  12. ↑ Hunter CM, Peterson AL, Alvarez LM, et al (2008). "Weight management using the internet a randomized controlled trial". Am J Prev Med 34 (2): 119–26. DOI:10.1016/j.amepre.2007.09.026. PMID 18201641. Research Blogging.
  13. ↑ Truby H et al. (2006). "Randomised controlled trial of four commercial weight loss programmes in the UK: initial findings from the BBC "diet trials"". BMJ 332: 1309-14. DOI:10.1136/bmj.38833.411204.80. PMID 16720619. Research Blogging.
  14. ↑ 14.0 14.1 Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ (2005). "Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial". JAMA 293 (1): 43-53. DOI:10.1001/jama.293.1.43. PMID 15632335. Research Blogging.
  15. ↑ Halton TL et al. (2006). "Low-carbohydrate-diet score and the risk of coronary heart disease in women". N Engl J Med 355: 1991-2002. DOI:10.1056/NEJMoa055317. PMID 17093250. Research Blogging.
  16. ↑ Pirozzo S et al. (2002). "Advice on low-fat diets for obesity". Cochrane database of systematic reviews (Online): CD003640. PMID 12076496. [e]
  17. ↑ Samaha FF, Iqbal N, Seshadri P, et al (2003). "A low-carbohydrate as compared with a low-fat diet in severe obesity". N. Engl. J. Med. 348 (21): 2074–81. DOI:10.1056/NEJMoa022637. PMID 12761364. Research Blogging.
  18. ↑ Foster GD et al. (2003). "A randomized trial of a low-carbohydrate diet for obesity". N Engl J Med 348: 2082–90. DOI:10.1056/NEJMoa022207. PMID 12761365. Research Blogging.
  19. ↑ Nordmann AJ et al. (2006). "Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials". Arch. Intern. Med. 166: 285-93. DOI:10.1001/archinte.166.3.285. PMID 16476868. Research Blogging.
  20. ↑ Howard BV et al. (2006). "Low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification Trial". JAMA 295: 39-49. DOI:10.1001/jama.295.1.39. PMID 16391215. Research Blogging.
  21. ↑ Howard BV et al. (2006). "Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial". JAMA 295: 655-66. DOI:10.1001/jama.295.6.655. PMID 16467234. Research Blogging.
  22. ↑ Prentice RL, Caan B, Chlebowski RT, et al (2006). "Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial". JAMA 295 (6): 629-42. DOI:10.1001/jama.295.6.629. PMID 16467232. Research Blogging.
  23. ↑ Beresford SA et al. (2006). "Low-fat dietary pattern and risk of colorectal cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial". JAMA 295: 643-54. DOI:10.1001/jama.295.6.643. PMID 16467233. Research Blogging.
  24. ↑ Gardner CD et al (2007). "Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial". JAMA 297: 969-77. DOI:10.1001/jama.297.9.969. PMID 17341711. Research Blogging.
  25. ↑ Ebbeling CB et al. (2007). "Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial". JAMA 297: 2092-102. DOI:10.1001/jama.297.19.2092. PMID 17507345. Research Blogging.
  26. ↑ Stern et al. (2004). "The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial". Ann Intern Med 140: 778–85. PMID 15148064. [e]
  27. ↑ Garg A et al. (1994). "Effects of varying carbohydrate content of diet in patients with non-insulin-dependent diabetes mellitus". JAMA 271: 1421–8. PMID 7848401. [e]
  28. ↑ 28.0 28.1 Thomas D, Elliott E, Baur L (2007). "Low glycaemic index or low glycaemic load diets for overweight and obesity" 3: CD005105. DOI:10.1002/14651858.CD005105.pub2. PMID 17636786. Research Blogging. Cite error: Invalid <ref> tag; name "pmid17636786" defined multiple times with different content
  29. ↑ Jenkins DJ et al. (1981). "Glycemic index of foods: a physiological basis for carbohydrate exchange". Am. J. Clin. Nutr. 34: 362-6. PMID 6259925. [e]
  30. ↑ Brand-Miller JC et al. (2003). "Physiological validation of the concept of glycemic load in lean young adults". J Nutr 133: 2728-32. PMID 12949357. [e]
  31. ↑ McMillan-Price J et al. (2006). "Comparison of 4 diets of varying glycemic load on weight loss and cardiovascular risk reduction in overweight and obese young adults: a randomized controlled trial". Arch. Intern. Med. 166: 1466-75. DOI:10.1001/archinte.166.14.1466. PMID 16864756. Research Blogging.
  32. ↑ 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.
  33. ↑ Richardson CR et al. (2008). "A meta-analysis of pedometer-based walking interventions and weight loss". Ann Fam Med (1): 69–77. DOI:10.1370/afm.761. PMID 18195317. Research Blogging.
  34. ↑ 34.0 34.1 Rucker D, Padwal R, Li SK, Curioni C, Lau DC (2007). "Long term pharmacotherapy for obesity and overweight: updated meta-analysis". BMJ. DOI:10.1136/bmj.39385.413113.25. PMID 18006966. Research Blogging.
  35. ↑ Christensen R et al. (2007). "Efficacy and safety of the weight-loss drug rimonabant: a meta-analysis of randomised trials". Lancet 370 (9600): 1706–13. DOI:10.1016/S0140-6736(07)61721-8. PMID 18022033. Research Blogging.
  36. ↑ Encinosa WE et al. (2006). "Healthcare utilization and outcomes after bariatric surgery". Medical Care 44: 706-12. DOI:10.1097/01.mlr.0000220833.89050.ed. PMID 16862031. Research Blogging.
  37. ↑ Mizón C et al. (2007). "Persistent anemia after Roux-en-Y gastric bypass". Nutrition 23: 277–80. DOI:10.1016/j.nut.2007.01.008. PMID 17352964. Research Blogging.
  38. ↑ Maggard MA et al. (2005). "Meta-analysis: surgical treatment of obesity". Ann. Intern. Med. 142: 547–59. PMID 15809466. [e]
  39. ↑ 39.0 39.1 Sjöström L et al. (2007). "Effects of bariatric surgery on mortality in Swedish obese subjects". N Engl J Med 357: 741-52. DOI:10.1056/NEJMoa066254. PMID 17715408. Research Blogging.
  40. ↑ 40.0 40.1 Adams TD et al. (2007). "Long-term mortality after gastric bypass surgery". N Engl J Med 357: 753-61. DOI:10.1056/NEJMoa066603. PMID 17715409. Research Blogging.
  41. ↑ Dixon JB, O'Brien PE, Playfair J, et al (January 2008). "Adjustable gastric banding and conventional therapy for type 2 diabetes: a randomized controlled trial". JAMA 299 (3): 316–23. DOI:10.1001/jama.299.3.316. PMID 18212316. Research Blogging.
  42. ↑ Rivera R. (2007) “New York City Reintroduces Calorie Rule,” The New York Times, October 25, 2007, http://www.nytimes.com/2007/10/25/nyregion/25calories.html (accessed October 26, 2007).
  43. ↑ Timlin MT, Pereira MA, Story M, Neumark-Sztainer D (2008). "Breakfast eating and weight change in a 5-year prospective analysis of adolescents: Project EAT (Eating Among Teens)". Pediatrics 121 (3): e638-45. DOI:10.1542/peds.2007-1035. PMID 18310183. Research Blogging.
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