Body mass index: Difference between revisions

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<math> \textrm{BMI} = \frac{ \textrm{W (kg)}}{\textrm{H (m)}^{2}} = 4.88 \frac{ \textrm{W (lbs)}}{\textrm{H (ft.)}^{2}} = 703 \frac{ \textrm{W (lbs.)}}{\textrm{H (in.)}^{2}}</math>.
<math> \textrm{BMI} = \frac{ \textrm{W (kg)}}{\textrm{H (m)}^{2}} = 4.88 \frac{ \textrm{W (lbs)}}{\textrm{H (ft.)}^{2}} = 703 \frac{ \textrm{W (lbs.)}}{\textrm{H (in.)}^{2}}</math>.


Healthy BMI is between 18.5 and 24.9.  Less than 18.5 is considered underweight; between 25 and 29.9 is considered overweight, over 30 is considered [[obesity|obese]], and over 40 is considered morbidly obese.
Healthy BMI is between 18.5 and 24.9.  Less than 18.5 is considered underweight; between 25 and 29.9 is considered overweight, over 30 is considered [[obesity|obese]], and over 45 is considered morbidly obese.


BMI is a rough diagnostic tool for estimating body fat, and has limitations. Chief among these are that it may overestimate body fat in athletes and others who have a muscular build, and that it may underestimate body fat in older persons and others who have lost muscle mass.<ref>http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations</ref>
A BMI over 25 or less than 22.5 is associated with increased mortality.<ref name="pmid19299006">{{cite journal |author=Whitlock G, Lewington S, Sherliker P, ''et al'' |title=Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies |journal=Lancet |volume=373 |issue=9669 |pages=1083–96 |year=2009 |month=March |pmid=19299006 |doi=10.1016/S0140-6736(09)60318-4 |url=http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(09)60318-4 |issn=}}</ref>
 
==BMI chart for adults==
{{Image|Adult-BMI-chart.jpg|center|700px|Find your BMI.}}
 
==Limitations and alternatives==
The BMI may overestimate percentage of body fat in athletes and others who have a muscular build, and may underestimate percentage of body fat in older persons and others who have lost muscle mass.<ref>http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations</ref>
 
Another limitation is in the choice of exponent. If humans scaled proportionally in all three dimensions as they become taller, the appropriate exponent would be 3, instead of the 2 used for BMI calculation.  However, 2 is too low.  Data from the United States indicates that an exponent of 2.6 is most appropriate.<ref>{{cite web|url=http://www.math.utah.edu/~korevaar/ACCESS2003/bmi.pdf|title=Notes on Body Mass Index and actual national data|date=July 2003|author=Nick Korevaar|publisher=University of Utah Math Department|format=PDF}}</ref>  Relatedly, the government of [[Singapore]] has set different cutoff levels of BMI, based on the shorter average stature and somewhat different body shape of Southeast Asians as compared to Europeans.<ref>{{cite web|url=http://www.hpb.gov.sg/hpb/default.asp?TEMPORARY_DOCUMENT=1769&TEMPORARY_TEMPLATE=2|title=Revision of Body Mass Index (BMI) Cut-offs in Singapore|date=2005-03-16|publisher=Health Promotion Board}}</ref>
 
An alternative anthropometric measure is the [[waist-to-hip ratio]].


==Notes==
==Notes==
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Body mass index (abbreviated BMI) is a rough measure of proportionality between a person's height and weight, and is used to estimate whether a person is at a healthy weight for their height. BMI is calculated as weight in kilograms divided by height in meters squared. For english units, a conversion factor is applied.

.

Healthy BMI is between 18.5 and 24.9. Less than 18.5 is considered underweight; between 25 and 29.9 is considered overweight, over 30 is considered obese, and over 45 is considered morbidly obese.

A BMI over 25 or less than 22.5 is associated with increased mortality.[1]

BMI chart for adults

PD U.S. Department of Health and Human Services. http://www.health.gov/dietaryguidelines/dga2005/healthieryou/html/chapter4.html
Find your BMI.

Limitations and alternatives

The BMI may overestimate percentage of body fat in athletes and others who have a muscular build, and may underestimate percentage of body fat in older persons and others who have lost muscle mass.[2]

Another limitation is in the choice of exponent. If humans scaled proportionally in all three dimensions as they become taller, the appropriate exponent would be 3, instead of the 2 used for BMI calculation. However, 2 is too low. Data from the United States indicates that an exponent of 2.6 is most appropriate.[3] Relatedly, the government of Singapore has set different cutoff levels of BMI, based on the shorter average stature and somewhat different body shape of Southeast Asians as compared to Europeans.[4]

An alternative anthropometric measure is the waist-to-hip ratio.

Notes

  1. ↑ Whitlock G, Lewington S, Sherliker P, et al (March 2009). "Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies". Lancet 373 (9669): 1083–96. DOI:10.1016/S0140-6736(09)60318-4. PMID 19299006. Research Blogging.
  2. ↑ http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations
  3. ↑ Nick Korevaar (July 2003). Notes on Body Mass Index and actual national data (PDF). University of Utah Math Department.
  4. ↑ Revision of Body Mass Index (BMI) Cut-offs in Singapore. Health Promotion Board (2005-03-16).
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