Editing Body mass index

{{Short description|Relative weight based on mass and height}}
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{{Infobox diagnostic
| name = Body mass index (BMI)
| synonyms = Quetelet index
| image = BMI chart.png
| alt =
| caption = Chart showing body mass index (BMI) for a range of heights and weights in both metric and imperial. Colours indicate [[#Categories|BMI categories]] defined by the [[World Health Organization]]; ''underweight'', ''normal weight'', ''overweight'', ''moderately obese'', ''severely obese'' and ''very severely obese''.
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| ICDO =
| MedlinePlus = 007196
| eMedicine = <!--article_number-->
| MeshID = D015992
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{{Human body weight}}

'''Body mass index''' ('''BMI''') is a value derived from the [[mass]] ([[Mass versus weight|weight]]) and [[height]] of a person. The BMI is defined as the [[human body weight|body mass]] divided by the [[square (algebra)|square]] of the [[human height|body height]], and is expressed in [[Units of measurement|units]] of kg/m<sup>2</sup>, resulting from mass in [[kilogram]]s (kg) and height in [[metre]]s (m).

The BMI may be determined first by measuring its components by means of a [[weighing scale]] and a [[stadiometer]]. The multiplication and division may be carried out directly, by hand or using a calculator, or indirectly using a [[lookup table]] (or chart).{{efn|e.g., the {{cite web | url = http://www.nhlbi.nih.gov/guidelines/obesity/bmi_tbl.htm | title = Body Mass Index Table | archive-url = https://web.archive.org/web/20100310114919/http://www.nhlbi.nih.gov/guidelines/obesity/bmi_tbl.htm | archive-date=2010-03-10 | publisher = [[National Institutes of Health]]'s [[National Heart, Lung, and Blood Institute|NHLBI]] }}}} The table displays BMI as a function of mass and height and may show other units of measurement (converted to [[Metric system|metric units]] for the calculation).{{efn|For example, in the UK where people often know their weight in [[Stone (unit)|stone]] and height in feet and inches – see {{cite news |url=http://news.bbc.co.uk/2/hi/health/5297790.stm |title=Calculate your body mass index |date=30 August 2006 |access-date=2019-12-11 }}}} The table may also show contour lines or colours for different BMI categories.

The BMI is a convenient [[rule of thumb]] used to broadly categorize a person as based on tissue mass ([[muscle]], [[fat]], and [[bone]]) and height. Major adult BMI classifications are ''[[underweight]]'' (under 18.5 kg/m<sup>2</sup>), ''[[Human body weight#Ideal_body_weight|normal weight]]'' (18.5 to 24.9), ''[[overweight]]'' (25 to 29.9), and ''[[obese]]'' (30 or more).<ref name="World Health Organization 2006" /> When used to predict an individual's health, rather than as a statistical measurement for groups, the BMI has [[#Limitations|limitations]] that can make it less useful than some of the [[#Alternatives|alternatives]], especially when applied to individuals with [[abdominal obesity]], [[short stature]], or [[Bodybuilding|high muscle mass]].

BMIs under 20 and over 25 have been associated with higher all-cause mortality, with the risk increasing with distance from the 20–25 range.<ref>{{cite journal | vauthors = Di Angelantonio E, Bhupathiraju S, Wormser D, Gao P, Kaptoge S, Berrington de Gonzalez A, Cairns BJ, Huxley R, Jackson C, Joshy G, Lewington S, Manson JE, Murphy N, Patel AV, Samet JM, Woodward M, Zheng W, Zhou M, Bansal N, Barricarte A, Carter B, Cerhan JR, Smith GD, Fang X, Franco OH, Green J, Halsey J, Hildebrand JS, Jung KJ, Korda RJ, McLerran DF, Moore SC, O'Keeffe LM, Paige E, Ramond A, Reeves GK, Rolland B, Sacerdote C, Sattar N, Sofianopoulou E, Stevens J, Thun M, Ueshima H, Yang L, Yun YD, Willeit P, Banks E, Beral V, Chen Z, Gapstur SM, Gunter MJ, Hartge P, Jee SH, Lam TH, Peto R, Potter JD, Willett WC, Thompson SG, Danesh J, Hu FB | title = Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents | journal = Lancet | volume = 388 | issue = 10046 | pages = 776–86 | date = August 2016 | pmid = 27423262 | pmc = 4995441 | doi = 10.1016/S0140-6736(16)30175-1 }}</ref>
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==History==
[[File:Obesity & BMI.png|thumb|Obesity and BMI]]
[[Adolphe Quetelet]], a Belgian [[astronomer]], mathematician, [[statistician]], and [[sociologist]], devised the basis of the BMI between 1830 and 1850 as he developed what he called "social physics".<ref>{{cite journal |vauthors=Eknoyan G |date=January 2008 |title=Adolphe Quetelet (1796–1874) – the average man and indices of obesity |journal=Nephrology, Dialysis, Transplantation |volume=23 |issue=1 |pages=47–51 |doi=10.1093/ndt/gfm517 |pmid=17890752 |doi-access=}}</ref> Quetelet himself never intended for the index, then called the Quetelet Index, to be used as a means of medical assessment. Instead, it was a component of his study of {{lang|fr|l'homme moyen}}, or the average man. Quetelet thought of the average man as a social ideal, and developed the body mass index as a means of discovering the socially ideal human person.<ref name=":0" /> According to Lars Grue and Arvid Heiberg in the Scandinavian Journal of Disability Research, Quetelet's idealization of the average man would be elaborated upon by [[Francis Galton]] a decade later in the development of [[Eugenics]].<ref>{{Cite journal |last=Heiberg |first=Arvid |date=2006-11-04 |title=Notes on the History of Normality – Reflections on the Work of Quetelet and Galton |journal=Scandinavian Journal of Disability Research |language=en-US |volume=8 |issue=4 |pages=232–246 |doi=10.1080/15017410600608491|doi-access=free }}</ref>

The modern term "body mass index" (BMI) for the ratio of [[human body weight]] to squared height was coined in a paper published in the July 1972 edition of the ''[[Journal of Chronic Diseases]]'' by [[Ancel Keys]] and others. In this paper, Keys argued that what he termed the BMI was "if not fully satisfactory, at least as good as any other relative weight index as an indicator of relative obesity".<ref>{{cite journal | vauthors = Blackburn H, Jacobs D | title = Commentary: Origins and evolution of body mass index (BMI): continuing saga | journal = International Journal of Epidemiology | volume = 43 | issue = 3 | pages = 665–669 | date = June 2014 | pmid = 24691955 | doi = 10.1093/ije/dyu061 | url = https://academic.oup.com/ije/article-pdf/43/3/665/9728399/dyu061.pdf | doi-access = free }}</ref><ref>{{cite magazine |url= http://www.slate.com/id/2223095/ |title= Beyond BMI: Why doctors won't stop using an outdated measure for obesity | vauthors = Singer-Vine J |magazine= [[Slate (magazine)|Slate]] |date= July 20, 2009 |access-date= 15 December 2013 |url-status=live |archive-url= https://web.archive.org/web/20110907125413/http://www.slate.com/id/2223095 |archive-date= 7 September 2011 }}</ref><ref>{{cite journal | vauthors = Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL | title = Indices of relative weight and obesity | journal = Journal of Chronic Diseases | volume = 25 | issue = 6 | pages = 329–343 | date = July 1972 | pmid = 4650929 | doi = 10.1016/0021-9681(72)90027-6 }}</ref>

The interest in an index that measures [[body fat]] came with observed increasing obesity in prosperous [[Western world|Western]] societies. Keys explicitly judged BMI as appropriate for ''population'' studies and inappropriate for individual evaluation. Nevertheless, due to its simplicity, it has come to be widely used for preliminary diagnoses.<ref name=nhlbi>{{cite web|title= Assessing Your Weight and Health Risk|url= http://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm|publisher= National Heart, Lung and Blood Institute|access-date= 19 December 2014|url-status=live|archive-url= https://web.archive.org/web/20141219195703/http://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm|archive-date=19 December 2014}}</ref> Additional metrics, such as waist circumference, can be more useful.<ref name=nhsob>{{cite web|title= Defining obesity|url= http://www.nhs.uk/Conditions/Obesity/Pages/Introduction.aspx|publisher= [[National Health Service|NHS]]|access-date= 19 December 2014|url-status=live|archive-url= https://web.archive.org/web/20141218121754/http://www.nhs.uk/Conditions/Obesity/Pages/Introduction.aspx|archive-date= 18 December 2014}}</ref>
{{BMI calculator|float=right}}
The BMI is expressed in kg/m<sup>2</sup>, resulting from mass in kilograms and height in metres. If [[Pound (mass)|pounds]] and [[inch]]es are used, a conversion factor of 703&nbsp;(kg/m<sup>2</sup>)/(lb/in<sup>2</sup>) is applied. (If pounds and feet are used, a conversion factor of 4.88 is used.) When the term BMI is used informally, the units are usually omitted.

<math display="block">\mathrm{BMI} = \frac{\text{mass}_\text{kg}}{{\text{height}_\text{m}}^2}
= \frac{\text{mass}_\text{lb}}{{\text{height}_\text{in}}^2}\times 703</math>

BMI provides a simple numeric measure of a person's ''thickness'' or ''thinness'', allowing health professionals to discuss weight problems more objectively with their patients. BMI was designed to be used as a simple means of classifying average sedentary (physically inactive) populations, with an average [[body composition]].<ref name="WHO: Physical status">{{cite journal | vauthors = <!--Staff writer(s); no by-line.--> | title = Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee | journal = World Health Organization Technical Report Series | volume = 854 | issue = 854 | pages = 1–452 | year = 1995 | pmid = 8594834 | url = <!-- derived from:http://www.who.int/childgrowth/publications/physical_status/en/-->http://whqlibdoc.who.int/trs/WHO_TRS_854.pdf | archive-url = https://web.archive.org/web/20070210134151/http://whqlibdoc.who.int/trs/WHO_TRS_854.pdf | url-status=live | archive-date = 2007-02-10 }}</ref> For such individuals, the BMI value recommendations {{as of | 2014 | lc = on}} are as follows: 18.5 to 24.9&nbsp;kg/m<sup>2</sup> may indicate optimal weight, lower than 18.5 may indicate [[underweight]], 25 to 29.9 may indicate [[overweight]], and 30 or more may indicate [[obesity|obese]].<ref name=nhlbi /><ref name=nhsob /> Lean male athletes often have a high muscle-to-fat ratio and therefore a BMI that is misleadingly high relative to their body-fat percentage.<ref name=nhsob />

==Categories==
A common use of the BMI is to assess how far an individual's body weight departs from what is normal for a person's height. The weight excess or deficiency may, in part, be accounted for by body fat ([[adipose tissue]]) although other factors such as muscularity also affect BMI significantly (see discussion below and [[overweight]]).<ref>{{Cite web|url=https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html|title=About Adult BMI {{!}} Healthy Weight|date=2017-08-29|website=CDC|language=en-us|access-date=2018-01-26}}</ref>

The [[World Health Organization|WHO]] regards an adult BMI of less than 18.5 as underweight and possibly indicative of [[malnutrition]], an [[eating disorder]], or other health problems, while a BMI of 25 or more is considered overweight and 30 or more is considered [[obesity|obese]].<ref name="World Health Organization 2006">{{cite book |url=https://apps.who.int/iris/bitstream/handle/10665/43190/9241593024_eng.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://apps.who.int/iris/bitstream/handle/10665/43190/9241593024_eng.pdf |archive-date=2022-10-09 |url-status=live |title=The SuRF Report 2 |series=The Surveillance of Risk Factors Report Series (SuRF) |page=22 |publisher=World Health Organization |date=2005 |ref={{harvid|World Health Organization|2005}}}}</ref> In addition to the principle, international WHO BMI cut-off points (16, 17, 18.5, 25, 30, 35 and 40), four additional cut-off points for at-risk Asians were identified (23, 27.5, 32.5 and 37.5).{{sfn|World Health Organization|2005|pp=21–22}} These ranges of BMI values are valid only as statistical categories.

{| class="wikitable plainrowheaders" style="text-align:center"
|+ BMI, basic categories
|-
! scope="col"| Category
! scope="col"| BMI (kg/m<sup>2</sup>){{efn|name="range-precision"}}
! scope="col"| [[#BMI prime (exponent of 2, normalization factor)|BMI Prime]]{{efn|name="range-precision"}}
|-
! scope="row"| Underweight (Severe thinness)
| < 16.0
| < 0.64
|-
! scope="row"| Underweight (Moderate thinness)
| class="nowrap"| 16.0–17.0
| class="nowrap"| 0.64–0.68
|-
! scope="row"| Underweight (Mild thinness)
| 17.0–18.5
| 0.68–0.74
|-
! scope="row"| Normal range
| 18.5–25.0
| 0.74–1.00
|-
! scope="row"| Overweight (Pre-obese)
| 25.0–30.0
| 1.00–1.20
|-
! scope="row"| Obese (Class I)
| 30.0–35.0
| 1.20–1.40
|-
! scope="row"| Obese (Class II)
| 35.0–40.0
| 1.40–1.60
|-
! scope="row"| Obese (Class III)
| ≥ 40.0
| ≥ 1.60
|}

===Children and youth===
[[File:BMIBoys 1.svg|thumb|upright=1.7|BMI for age percentiles for boys 2 to 20 years of age]]
[[File:BMIGirls 1.svg|thumb|upright=1.7|BMI for age percentiles for girls 2 to 20 years of age]]
BMI is used differently for people aged 2 to 20. It is calculated in the same way as for adults but then compared to typical values for other children or youth of the same age. Instead of comparison against fixed thresholds for underweight and overweight, the BMI is compared against the [[percentile]]s for children of the same sex and age.<ref>{{cite web|url = https://www.cdc.gov/nccdphp/dnpa/healthyweight/assessing/bmi/childrens_BMI/about_childrens_BMI.htm|title = Body Mass Index: BMI for Children and Teens|publisher = Center for Disease Control|access-date = 2013-12-16|url-status=live|archive-url = https://web.archive.org/web/20131029061522/http://www.cdc.gov/nccdphp/dnpa/healthyweight/assessing/bmi/childrens_BMI/about_childrens_BMI.htm|archive-date = 2013-10-29}}</ref>

A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered obese. Children with a BMI between the 85th and 95th percentile are considered to be overweight.<ref>{{cite book | chapter = Chapter 2: Use of Percentiles and Z-Scores in Anthropometry | title = Handbook of Anthropometry| vauthors = Wang Y |publisher=Springer|year=2012|isbn=978-1-4419-1787-4|location=New York|pages=29}}</ref>

Studies in Britain from 2013 have indicated that females between the ages 12 and 16 had a higher BMI than males of the same age by 1.0&nbsp;kg/m<sup>2</sup> on average.<ref>{{cite web|url = http://www.archive2.official-documents.co.uk/document/deps/doh/survey02/summ03.htm|title = Health Survey for England: The Health of Children and Young People|website = Archive2.official-documents.co.uk|access-date = 16 December 2013|url-status=dead|archive-url = https://web.archive.org/web/20120625003857/http://www.archive2.official-documents.co.uk/document/deps/doh/survey02/summ03.htm|archive-date = 2012-06-25}}</ref>

===International variations===
These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic. People from different populations and descent have different associations between BMI, percentage of body fat, and health risks, with a higher risk of [[type 2 diabetes mellitus]] and [[Atherosclerosis|atherosclerotic]] cardiovascular disease at BMIs lower than the [[World Health Organization|WHO]] cut-off point for overweight, 25&nbsp;kg/m<sup>2</sup>, although the cut-off for observed risk varies among different populations. The cut-off for observed risk varies based on populations and subpopulations in Europe, Asia and Africa.<ref>{{cite journal| vauthors = Ogunlade O, Adalumo OA, Asafa MA |title= Challenges of body mass index classification: New criteria for young adult Nigerians|journal= Niger J Health Sci |year=2015|volume= 15|issue=15:71–4|page= 71|doi= 10.4103/1596-4078.182319|doi-broken-date= 1 November 2024|s2cid= 132117809|doi-access= free}}</ref><ref>{{cite journal | title = Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies | journal = Lancet | volume = 363 | issue = 9403 | pages = 157–163 | date = January 2004 | pmid = 14726171 | doi = 10.1016/S0140-6736(03)15268-3 | author1 = WHO Expert Consultation | s2cid = 15637224 }}</ref>

====Hong Kong====
The [[Hospital Authority]] of [[Hong Kong]] recommends the use of the following BMI ranges:<ref name="ha">{{cite web |url=https://www.fitnessofbody.com/2019/04/body-weight-chart.html |title=Body weight chart – ideal goal weight chart |publisher=Fitness of Body – Health & Wellness site |language=en |access-date=2019-04-21 |archive-date=2021-03-08 |archive-url=https://web.archive.org/web/20210308091202/https://www.fitnessofbody.com/2019/04/body-weight-chart.html |url-status=dead }}</ref>

{| class="wikitable plainrowheaders" style="text-align:center"
|+ BMI in Hong Kong
|-
! scope="col"| Category
! scope="col"| BMI (kg/m<sup>2</sup>){{efn|name="range-precision"}}
|-
! scope="row"| Underweight (Unhealthy)
| < 18.5
|-
! scope="row"| Normal range (Healthy)
| class="nowrap"| 18.5–22.9
|-
! scope="row"| Overweight I (At risk)
| 23.0–24.9
|-
! scope="row"| Overweight II (Moderately obese)
| 25.0–29.9
|-
! scope="row"| Overweight III (Severely obese)
| ≥ 30.0
|}

====Japan====
A 2000 study from the Japan Society for the Study of Obesity (JASSO) presents the following table of BMI categories:<ref name="himan-mhlw">{{cite web |url=http://www.mhlw.go.jp/topics/bukyoku/kenkou/seikatu/himan/about.html |title={{as written|肥満って、 どんな状態？}} |trans-title=What is obesity, what kind of state? |work=Obesity Homepage<!--肥満ホームページ--> |publisher=Ministry of Health, Labor and Welfare<!--厚生労働省--> |access-date=2013-05-25 |language=ja |url-status=dead |archive-url=https://web.archive.org/web/20130628232937/http://www.mhlw.go.jp/topics/bukyoku/kenkou/seikatu/himan/about.html |archive-date=2013-06-28 }}</ref><ref>{{cite journal | vauthors = Shiwaku K, Anuurad E, Enkhmaa B, Nogi A, Kitajima K, Shimono K, Yamane Y, Oyunsuren T | title = Overweight Japanese with body mass indexes of 23.0–24.9 have higher risks for obesity-associated disorders: a comparison of Japanese and Mongolians | journal = International Journal of Obesity and Related Metabolic Disorders | volume = 28 | issue = 1 | pages = 152–158 | date = January 2004 | pmid = 14557832 | doi = 10.1038/sj.ijo.0802486 | s2cid = 287574 | doi-access =  }}</ref><ref>{{cite journal | vauthors = Kanazawa M, Yoshiike N, Osaka T, Numba Y, Zimmet P, Inoue S | title = Criteria and classification of obesity in Japan and Asia-Oceania. | journal = Asia Pacific Journal of Clinical Nutrition | date = December 2002 | volume = 11 | pages = S732-7 | doi = 10.1046/j.1440-6047.11.s8.19.x | url = https://apjcn.nhri.org.tw/server/APJCN/11/s7/S732.pdf }}{{rp| S734}}</ref>

{| class="wikitable plainrowheaders" style="text-align:center"
|+ BMI in Japan
|-
! scope="col"| Category
! scope="col"| BMI (kg/m<sup>2</sup>){{efn|name="range-precision"}}
|-
! scope="row"| Underweight (Thin)
| < 18.5
|-
! scope="row"| Normal weight
| class="nowrap"| 18.5–24.9
|-
! scope="row"| Obesity (Class 1)
| 25.0–29.9
|-
! scope="row"| Obesity (Class 2)
| 30.0–34.9
|-
! scope="row"| Obesity (Class 3)
| 35.0–39.9
|-
! scope="row"| Obesity (Class 4)
| ≥ 40.0
|}

====Singapore====
In Singapore, the BMI cut-off figures were revised in 2005 by the [[Health Promotion Board]] (HPB), motivated by studies showing that many Asian populations, including Singaporeans, have a higher proportion of body fat and increased risk for cardiovascular diseases and [[diabetes mellitus]], compared with general BMI recommendations in other countries. The BMI cut-offs are presented with an emphasis on health risk rather than weight.<ref>{{cite web |url=http://cardiology.com.sg/body-mass-index-bmi/|title=Body Mass Index (BMI) |website=Peter Yan Cardiology Clinic |access-date=8 July 2021}}</ref>

{| class="wikitable plainrowheaders"
|+ BMI in Singapore
|-
! scope="col"| Category
! scope="col"| BMI (kg/m<sup>2</sup>){{efn|name="range-precision"}}
! scope="col"| Health risk
|-
! scope="row"| Underweight
| style="text-align:center"| < 18.5
| Possible nutritional deficiency and osteoporosis.
|-
! scope="row"| Normal
| style="text-align:center" class="nowrap"| 18.5–22.9
| Low risk (healthy range).
|-
! scope="row"| Mild to moderate overweight
| style="text-align:center"| 23.0–27.4
| Moderate risk of developing heart disease, high blood pressure, stroke, diabetes mellitus.
|-
! scope="row"| Very overweight to obese
| style="text-align:center"| ≥ 27.5
| High risk of developing heart disease, high blood pressure, stroke, diabetes mellitus. [[Metabolic syndrome]].
|}

==== United Kingdom ====
In the UK, [[National Institute for Health and Care Excellence|NICE]] guidance recommends prevention of type 2 diabetes should start at a BMI of 30 in White and 27.5 in [[Black British people|Black African]], [[British African-Caribbean people|African-Caribbean]], [[South Asians in the United Kingdom|South Asian]], and [[British Chinese|Chinese]] populations.<ref>{{Cite journal |date=2022-07-26 |title=Diabetes: putting people at the heart of services |url=https://evidence.nihr.ac.uk/collection/diabetes-putting-people-at-the-heart-of-services/ |journal=NIHR Evidence |type=Plain English summary |language=en |publisher=National Institute for Health and Care Research |doi=10.3310/nihrevidence_52026 |s2cid=251299176|url-access=subscription }}</ref>

Research since 2021 based on a large sample of almost 1.5 million people in England found that some ethnic groups would benefit from prevention at or above a BMI of (rounded):<ref>{{Cite journal |date=2022-03-10 |title=Are you at risk of diabetes? Research finds prevention should start at a different BMI for each ethnic group |url=https://evidence.nihr.ac.uk/alert/diabetes-prevention-should-start-at-different-bmi-for-each-ethnic-group/ |journal=NIHR Evidence |type=Plain English summary |language=en |publisher=National Institute for Health and Care Research |doi=10.3310/alert_48878 |s2cid=247390548|url-access=subscription }}</ref><ref>{{cite journal | vauthors = Caleyachetty R, Barber TM, Mohammed NI, Cappuccio FP, Hardy R, Mathur R, Banerjee A, Gill P | title = Ethnicity-specific BMI cutoffs for obesity based on type 2 diabetes risk in England: a population-based cohort study | journal = The Lancet. Diabetes & Endocrinology | volume = 9 | issue = 7 | pages = 419–426 | date = July 2021 | pmid = 33989535 | pmc = 8208895 | doi = 10.1016/S2213-8587(21)00088-7 }}</ref>
* 30 in White
* 28 in Black
** just below 30 in Black British
** 29 in Black African
** 27 in Black Other
** 26 in Black Caribbean
* 27 in Arab and Chinese
* 24 in South Asian
** 24 in Pakistani, Indian and Nepali
** 23 in Tamil and Sri Lankan
** 21 in [[British Bangladeshis|Bangladeshi]]

====United States====
In 1998, the U.S. [[National Institutes of Health]] brought U.S. definitions in line with [[World Health Organization]] guidelines, lowering the normal/overweight cut-off from a BMI of 27.8 (men) and 27.3 (women) to a BMI of 25. This had the effect of redefining approximately 25 million Americans, previously ''healthy'', to ''overweight''.<ref name = "CNN_1998">{{cite news | url=http://www.cnn.com/HEALTH/9806/17/weight.guidelines/ | title=Who's fat? New definition adopted | publisher=CNN | date=June 17, 1998 | access-date=2010-04-26 | url-status=live | archive-url=https://web.archive.org/web/20101122173108/http://www.cnn.com/HEALTH/9806/17/weight.guidelines/ | archive-date=November 22, 2010 }}</ref><ref>{{cite journal |last=Nuttall |first=Frank Q. |date=2015-04-07 |title=Body Mass Index – Obesity, BMI, and Health: A Critical Review |journal=Nutrition Today |volume=50 |issue=3 |pages=117–128 |doi=10.1097/NT.0000000000000092 |pmc=4890841 |pmid=27340299}}</ref>

This can partially explain the increase in the ''overweight'' diagnosis in the past 20 years,{{when|date=February 2023}} and the increase in sales of weight loss products during the same time. [[World Health Organization|WHO]] also recommends lowering the normal/overweight threshold for southeast Asian body types to around BMI 23, and expects further revisions to emerge from clinical studies of different body types.<ref>{{Cite journal|last=World Health Organization|date=January 10, 2004|title=Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies|url=https://www.who.int/nutrition/publications/bmi_asia_strategies.pdf|archive-url=https://web.archive.org/web/20061210180811/http://www.who.int/nutrition/publications/bmi_asia_strategies.pdf|url-status=dead|archive-date=December 10, 2006|journal=The Lancet|volume=363|issue=9403|pages=157–163|doi=10.1016/s0140-6736(03)15268-3|pmid=14726171|s2cid=15637224}}</ref>

A survey in 2007 showed 63% of Americans were then overweight or obese, with 26% in the obese category (a BMI of 30 or more). By 2014, 37.7% of adults in the United States were obese, 35.0% of men and 40.4% of women; class 3 obesity (BMI over 40) values were 7.7% for men and 9.9% for women.<ref>{{cite journal | vauthors = Flegal KM, Kruszon-Moran D, Carroll MD, Fryar CD, Ogden CL | title = Trends in Obesity Among Adults in the United States, 2005 to 2014 | journal = JAMA | volume = 315 | issue = 21 | pages = 2284–2291 | date = June 2016 | pmid = 27272580 | doi = 10.1001/jama.2016.6458 | doi-access = free | pmc = 11197437 }}</ref> The U.S. National Health and Nutrition Examination Survey of 2015–2016 showed that 71.6% of American men and women had BMIs over 25.<ref>{{cite web|url=https://www.cdc.gov/nchs/data/hus/2018/021.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.cdc.gov/nchs/data/hus/2018/021.pdf |archive-date=2022-10-09 |url-status=live|title= Selected health conditions and risk factors, by age: the United States, selected years}}</ref> Obesity—a BMI of 30 or more—was found in 39.8% of the US adults.

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{| class="wikitable plainrowheaders floatleft"
|-
|+ Body mass index values (kg/m<sup>2</sup>) for males aged 20 and over, and selected percentiles by age: United States, 2011–2014<ref name="CDC-Anthropometric">{{cite web|url=https://www.cdc.gov/nchs/data/series/sr_03/sr03_039.pdf|title=Anthropometric Reference Data for Children and Adults: United States|publisher=[[Centers for Disease Control and Prevention|CDC DHHS]]|date=2016|url-status=live|archive-url=https://web.archive.org/web/20170202010330/https://www.cdc.gov/nchs/data/series/sr_03/sr03_039.pdf|archive-date=2017-02-02}}</ref>
|-
! scope="col" rowspan="2"| Age
! scope="colgroup" colspan="9"| Percentile
|-
! scope="col"| 5th
! scope="col"| 10th
! scope="col"| 15th
! scope="col"| 25th
! scope="col"| 50th
! scope="col"| 75th
! scope="col"| 85th
! scope="col"| 90th
! scope="col"| 95th
|-
! scope="row" style="text-align:center"| ≥ 20 (total)
| 20.7
| 22.2
| 23.0
| 24.6
| 27.7
| 31.6
| 34.0
| 36.1
| 39.8
|-
! scope="row" style="text-align:center" class="nowrap"| 20–29
| 19.3
| 20.5
| 21.2
| 22.5
| 25.5
| 30.5
| 33.1
| 35.1
| 39.2
|-
! scope="row" style="text-align:center"| 30–39
| 21.1
| 22.4
| 23.3
| 24.8
| 27.5
| 31.9
| 35.1
| 36.5
| 39.3
|-
! scope="row" style="text-align:center"| 40–49
| 21.9
| 23.4
| 24.3
| 25.7
| 28.5
| 31.9
| 34.4
| 36.5
| 40.0
|-
! scope="row" style="text-align:center"| 50–59
| 21.6
| 22.7
| 23.6
| 25.4
| 28.3
| 32.0
| 34.0
| 35.2
| 40.3
|-
! scope="row" style="text-align:center"| 60–69
| 21.6
| 22.7
| 23.6
| 25.3
| 28.0
| 32.4
| 35.3
| 36.9
| 41.2
|-
! scope="row" style="text-align:center"| 70–79
| 21.5
| 23.2
| 23.9
| 25.4
| 27.8
| 30.9
| 33.1
| 34.9
| 38.9
|-
! scope="row" style="text-align:center"| ≥ 80
| 20.0
| 21.5
| 22.5
| 24.1
| 26.3
| 29.0
| 31.1
| 32.3
| 33.8
|}

{| class="wikitable plainrowheaders"
|-
|+ Body mass index values (kg/m<sup>2</sup>) for females aged 20 and over, and selected percentiles by age: United States, 2011–2014<ref name="CDC-Anthropometric" />
|-
! scope="col" rowspan="2"| Age
! scope="colgroup" colspan="9"| Percentile
|-
! scope="col"| 5th
! scope="col"| 10th
! scope="col"| 15th
! scope="col"| 25th
! scope="col"| 50th
! scope="col"| 75th
! scope="col"| 85th
! scope="col"| 90th
! scope="col"| 95th
|-
! scope="row" style="text-align:center"| ≥ 20 (total)
| 19.6
| 21.0
| 22.0
| 23.6
| 27.7
| 33.2
| 36.5
| 39.3
| 43.3
|-
! scope="row" style="text-align:center" class="nowrap"| 20–29
| 18.6
| 19.8
| 20.7
| 21.9
| 25.6
| 31.8
| 36.0
| 38.9
| 42.0
|-
! scope="row" style="text-align:center"| 30–39
| 19.8
| 21.1
| 22.0
| 23.3
| 27.6
| 33.1
| 36.6
| 40.0
| 44.7
|-
! scope="row" style="text-align:center"| 40–49
| 20.0
| 21.5
| 22.5
| 23.7
| 28.1
| 33.4
| 37.0
| 39.6
| 44.5
|-
! scope="row" style="text-align:center"| 50–59
| 19.9
| 21.5
| 22.2
| 24.5
| 28.6
| 34.4
| 38.3
| 40.7
| 45.2
|-
! scope="row" style="text-align:center"| 60–69
| 20.0
| 21.7
| 23.0
| 24.5
| 28.9
| 33.4
| 36.1
| 38.7
| 41.8
|-
! scope="row" style="text-align:center"| 70–79
| 20.5
| 22.1
| 22.9
| 24.6
| 28.3
| 33.4
| 36.5
| 39.1
| 42.9
|-
! scope="row" style="text-align:center"| ≥ 80
| 19.3
| 20.4
| 21.3
| 23.3
| 26.1
| 29.7
| 30.9
| 32.8
| 35.2
|}
{{clear}}
</div>

==Consequences of elevated level in adults==
The BMI ranges are based on the relationship between body weight and disease and death.<ref name="WHO: Physical status"/> Overweight and obese individuals are at an increased risk for the following diseases:<ref>{{cite book |chapter=Executive Summary |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK2008/ |pages=xi–xxx |no-pp=y |date=September 1998 |title=Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report |url=http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm |publisher=[[National Heart, Lung, and Blood Institute]] |url-status=live |archive-url=https://web.archive.org/web/20130103083355/http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm |archive-date=2013-01-03 }}</ref>
* [[Coronary artery disease]]
* [[Dyslipidemia]]
* [[Diabetes mellitus type 2|Type 2 diabetes]]
* [[Gallbladder disease]]
* [[Hypertension]]
* [[Osteoarthritis]]
* [[Sleep apnea]]
* [[Stroke]]
* [[Infertility]]
* At least 10 cancers, including [[Endometrial cancer|endometrial]], [[Breast cancer|breast]], and [[colon cancer]]<ref>{{cite journal | vauthors = Bhaskaran K, Douglas I, Forbes H, dos-Santos-Silva I, Leon DA, Smeeth L | title = Body-mass index and risk of 22 specific cancers: a population-based cohort study of 5·24 million UK adults | journal = Lancet | volume = 384 | issue = 9945 | pages = 755–765 | date = August 2014 | pmid = 25129328 | pmc = 4151483 | doi = 10.1016/S0140-6736(14)60892-8 | url = }}</ref>
* Epidural [[lipomatosis]]<ref>{{cite journal|title=Multiple epidural steroid injections and body mass index linked with occurrence of epidural lipomatosis: a case series| doi=10.1186/1471-2253-14-70|pmid = 25183952| pmc=4145583|volume=14| pages=70|year=2014|journal=BMC Anesthesiology| vauthors= Jaimes R, Rocco AG | doi-access=free}}</ref>

Among people who have never smoked, overweight/obesity is associated with 51% increase in mortality compared with people who have always been a normal weight.<ref>{{cite journal | vauthors = Stokes A, Preston SH | title = Smoking and reverse causation create an obesity paradox in cardiovascular disease | journal = Obesity | volume = 23 | issue = 12 | pages = 2485–2490 | date = December 2015 | pmid = 26421898 | pmc = 4701612 | doi = 10.1002/oby.21239 }}</ref>

==Applications==

===Public health===
The BMI is generally used as a means of correlation between groups related by general mass and can serve as a vague means of estimating [[adipose tissue|adiposity]]. The duality of the BMI is that, while it is easy to use as a general calculation, it is limited as to how accurate and pertinent the data obtained from it can be. Generally, the index is suitable for recognizing trends within sedentary or overweight individuals because there is a smaller margin of error.<ref name="jxbvhf">{{cite book | vauthors = Jeukendrup A, Gleeson M |author-link1=Asker Jeukendrup |year=2005 |title=Sports Nutrition |publisher=Human Kinetics: An Introduction to Energy Production and Performance |isbn=978-0-7360-3404-3}}{{page needed|date=April 2012}}</ref> The BMI has been used by the [[World Health Organization|WHO]] as the standard for recording obesity statistics since the early 1980s.

This general correlation is particularly useful for consensus data regarding obesity or various other conditions because it can be used to build a semi-accurate representation from which a solution can be stipulated, or the [[Recommended Dietary Allowance|RDA]] for a group can be calculated. Similarly, this is becoming more and more pertinent to the growth of children, since the majority of children are sedentary.<ref>{{cite book | vauthors = Barasi ME |year=2004 |title=Human Nutrition – a health perspective |publisher=CRC Press |isbn=978-0-340-81025-5}}{{page needed|date=April 2012}}</ref>
Cross-sectional studies indicated that sedentary people can decrease BMI by becoming more physically active. Smaller effects are seen in prospective cohort studies which lend to support [[active mobility]] as a means to prevent a further increase in BMI.<ref name="Dons">{{cite journal | vauthors = Dons E, Rojas-Rueda D, Anaya-Boig E, Avila-Palencia I, Brand C, Cole-Hunter T, de Nazelle A, Eriksson U, Gaupp-Berghausen M, Gerike R, Kahlmeier S, Laeremans M, Mueller N, Nawrot T, Nieuwenhuijsen MJ, Orjuela JP, Racioppi F, Raser E, Standaert A, Int Panis L, Götschi T | title = Transport mode choice and body mass index: Cross-sectional and longitudinal evidence from a European-wide study | journal = Environment International | volume = 119 | issue = 119 | pages = 109–116 | date = October 2018 | pmid = 29957352 | doi = 10.1016/j.envint.2018.06.023 | bibcode = 2018EnInt.119..109D | hdl-access = free | hdl = 10044/1/61061 | s2cid = 49607716 | url = https://www.zora.uzh.ch/id/eprint/152336/1/Dons2018_preprint_BMI.pdf }}</ref>

===Legislation===
In France, Italy, and Spain, legislation has been introduced banning the usage of fashion show models having a BMI below 18.<ref>{{cite magazine|url=https://time.com/3770696/france-banned-ultra-thin-models/|title=France Just Banned Ultra-Thin Models| vauthors = Stampler L |magazine=[[Time (magazine)|Time]] |url-status=live|archive-url=https://web.archive.org/web/20150410084813/http://time.com/3770696/france-banned-ultra-thin-models/|archive-date=2015-04-10}}</ref> In Israel, a model with BMI below 18.5 is banned.<ref>{{cite web|url=https://abcnews.go.com/International/israeli-law-bans-skinny-bmi-challenged-models/story?id=18116291|title=Israeli Law Bans Skinny, BMI-Challenged Models|author=ABC News|work=ABC News|url-status=live|archive-url=https://web.archive.org/web/20141210120342/https://abcnews.go.com/International/israeli-law-bans-skinny-bmi-challenged-models/story?id=18116291|archive-date=2014-12-10}}</ref> This is done to fight [[Anorexia nervosa|anorexia]] among models and people interested in fashion.

==Relationship to health==
A study published by ''[[Journal of the American Medical Association]]'' (''JAMA'') in 2005 showed that ''overweight'' people had a death rate similar to ''normal'' weight people as defined by BMI, while ''underweight'' and ''obese'' people had a higher death rate.<ref>{{cite journal | vauthors = Flegal KM, Graubard BI, Williamson DF, Gail MH | title = Excess deaths associated with underweight, overweight, and obesity | journal = JAMA | volume = 293 | issue = 15 | pages = 1861–1867 | date = April 2005 | pmid = 15840860 | doi = 10.1001/jama.293.15.1861 | doi-access =  }}</ref>

A study published by ''[[The Lancet]]'' in 2009 involving 900,000 adults showed that ''overweight'' and ''underweight'' people both had a mortality rate higher than ''normal'' weight people as defined by BMI. The optimal BMI was found to be in the range of 22.5–25.<ref>{{cite journal | vauthors = Whitlock G, Lewington S, Sherliker P, Clarke R, Emberson J, Halsey J, Qizilbash N, Collins R, Peto R | 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 = 1083–1096 | date = March 2009 | pmid = 19299006 | pmc = 2662372 | doi = 10.1016/S0140-6736(09)60318-4 }}</ref> The average BMI of athletes is 22.4 for women and 23.6 for men.<ref>{{cite journal | vauthors = Walsh J, Heazlewood IT, Climstein M | title = Body Mass Index in Master Athletes: Review of the Literature | journal = Journal of Lifestyle Medicine | volume = 8 | issue = 2 | pages = 79–98 | date = July 2018 | pmid = 30474004 | pmc = 6239137 | doi = 10.15280/jlm.2018.8.2.79 }}</ref>

High BMI is associated with [[diabetes mellitus type 2|type&nbsp;2 diabetes]] only in people with high serum [[gamma-glutamyl transpeptidase]].<ref name="pmid17478563">{{cite journal | vauthors = Lim JS, Lee DH, Park JY, Jin SH, Jacobs DR | title = A strong interaction between serum gamma-glutamyltransferase and obesity on the risk of prevalent type 2 diabetes: results from the Third National Health and Nutrition Examination Survey | journal = Clinical Chemistry | volume = 53 | issue = 6 | pages = 1092–1098 | date = June 2007 | pmid = 17478563 | doi = 10.1373/clinchem.2006.079814 | doi-access = free }}</ref>

In an analysis of 40 studies involving 250,000 people, patients with coronary artery disease with ''normal'' BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the ''overweight'' range (BMI 25–29.9).<ref>{{cite journal | vauthors = Romero-Corral A, Montori VM, Somers VK, Korinek J, Thomas RJ, Allison TG, Mookadam F, Lopez-Jimenez F | title = Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: a systematic review of cohort studies | journal = Lancet | volume = 368 | issue = 9536 | pages = 666–678 | date = August 2006 | pmid = 16920472 | doi = 10.1016/S0140-6736(06)69251-9 | s2cid = 23306195 }}</ref>

One study found that BMI had a good general correlation with body fat percentage, and noted that obesity has overtaken smoking as the world's number one cause of death. But it also notes that in the study 50% of men and 62% of women were obese according to body fat defined obesity, while only 21% of men and 31% of women were obese according to BMI, meaning that BMI was found to underestimate the number of obese subjects.<ref name="RomeroCorral2008"/>

A 2010 study that followed 11,000 subjects for up to eight years concluded that BMI is not the most appropriate measure for the risk of heart attack, stroke or death. A better measure was found to be the [[waist-to-height ratio]].<ref>{{cite journal | vauthors = Schneider HJ, Friedrich N, Klotsche J, Pieper L, Nauck M, John U, Dörr M, Felix S, Lehnert H, Pittrow D, Silber S, Völzke H, Stalla GK, Wallaschofski H, Wittchen HU | title = The predictive value of different measures of obesity for incident cardiovascular events and mortality | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 95 | issue = 4 | pages = 1777–1785 | date = April 2010 | pmid = 20130075 | doi = 10.1210/jc.2009-1584 | doi-access = free }}</ref> A 2011 study that followed 60,000 participants for up to 13 years found that [[waist–hip ratio]] was a better predictor of ischaemic heart disease mortality.<ref name= "MørkedalRomundstad2011">{{cite journal | vauthors = Mørkedal B, Romundstad PR, Vatten LJ | title = Informativeness of indices of blood pressure, obesity and serum lipids in relation to ischaemic heart disease mortality: the HUNT-II study | journal = European Journal of Epidemiology | volume = 26 | issue = 6 | pages = 457–461 | date = June 2011 | pmid = 21461943 | pmc = 3115050 | doi = 10.1007/s10654-011-9572-7 }}</ref>

==Limitations==
[[File:Correlation between BMI and Percent Body Fat for Men in NCHS' NHANES 1994 Data.PNG|right|thumb|upright=1.7|This graph shows the correlation between body mass index (BMI) and body fat percentage (BFP) for 8550 men in [[National Center for Health Statistics|NCHS]]' [[National Health and Nutrition Examination Survey|NHANES]] 1994 data. Data in the upper left and lower right quadrants suggest the limitations of BMI.<ref name="RomeroCorral2008">{{cite journal | vauthors = Romero-Corral A, Somers VK, Sierra-Johnson J, Thomas RJ, Collazo-Clavell ML, Korinek J, Allison TG, Batsis JA, Sert-Kuniyoshi FH, Lopez-Jimenez F | title = Accuracy of body mass index in diagnosing obesity in the adult general population | journal = International Journal of Obesity | volume = 32 | issue = 6 | pages = 959–966 | date = June 2008 | pmid = 18283284 | pmc = 2877506 | doi = 10.1038/ijo.2008.11 }}</ref>]]
The medical establishment<ref>{{cite web |url=http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations |title=Aim for a Healthy Weight: Assess your Risk |publisher=National Institutes of Health |date=July 8, 2007 |access-date=15 December 2013 |url-status=live |archive-url=https://web.archive.org/web/20131216071225/http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations |archive-date=16 December 2013 }}</ref> and statistical community<ref>{{cite journal | vauthors = Kronmal RA | year = 1993 | title = Spurious correlation and the fallacy of the ratio standard revisited | journal = Journal of the Royal Statistical Society | volume = 156 | issue = 3| pages = 379–392 | doi = 10.2307/2983064 | jstor = 2983064 }}</ref> have both highlighted the limitations of BMI. 

=== Racial and gender differences ===
Part of the statistical limitations of the BMI scale is the result of Quetelet's original sampling methods.<ref name=":1">{{Cite book |last=Strings |first=Sabrina |url=http://worldcat.org/oclc/1256003500 |title=Fearing the black body : the racial origins of fat phobia |year=2019 |publisher=New York University Press |isbn=978-1-4798-9178-8 |oclc=1256003500}}</ref> As noted in his primary work, ''A Treatise on Man and the Development of His Faculties'', the data from which Quetelet derived his formula was taken mostly from Scottish Highland soldiers and French [[Gendarmerie]].<ref name=":0" /> The BMI was always designed as a metric for European men. For women, and people of non-European origin, the scale is often biased. As noted by sociologist Sabrina Strings, the BMI is largely inaccurate for black people especially, disproportionately labelling them as overweight even for healthy individuals.<ref name=":1" />{{Verify source|date=January 2025}} A 2012 study of BMI in an ethnically diverse population showed that "adult overweight and obesity were associated with an increased risk of mortality ... across the five racial/ethnic groups".<ref>{{cite journal | title = Body mass index and mortality in an ethnically diverse population: the Multiethnic Cohort Study | journal = The Health Board | date = 9 September 2023 | pmc = 4494097 | volume = 27 | issue = 7 | pages = 489–497 | doi = 10.1007/s10654-012-9695-5 | pmid = 22644110 | vauthors = Park SY, Wilkens LR, Murphy SP, Monroe KR, Henderson BE, Kolonel LN }}</ref>

===Scaling===
The BMI depends upon weight and the ''square'' of height. Since mass increases to the ''third power'' of linear dimensions, taller individuals with exactly the same body shape and relative composition have a larger BMI.<ref>{{cite journal | vauthors = Taylor RS | title = Letter to the editor | journal = Paediatrics & Child Health | volume = 15 | issue = 5 | pages = 258 | date = May 2010 | pmid = 21532785 | pmc = 2912631 | doi=10.1093/pch/15.5.258}}</ref> BMI is proportional to the mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels. In comparison, the [[Ponderal index]] is based on the natural scaling of mass with the third power of the height.<ref>{{cite web | vauthors = Bonderud D | title = What is the Ponderal Index? | work = The Health Board | date = 9 September 2023 | url = https://www.infobloom.com/what-is-the-ponderal-index.htm}}</ref>

However, many taller people are not just "scaled up" short people but tend to have narrower frames in proportion to their height.<ref>{{cite journal | vauthors = Sperrin M, Marshall AD, Higgins V, Renehan AG, Buchan IE | title = Body mass index relates weight to height differently in women and older adults: serial cross-sectional surveys in England (1992-2011) | journal = Journal of Public Health | volume = 38 | issue = 3 | pages = 607–613 | date = September 2016 | pmid = 26036702 | pmc = 5072155 | doi = 10.1093/pubmed/fdv067 }}</ref> [[Carl Lavie]] has written that "The B.M.I. tables are excellent for identifying obesity and body fat in large populations, but they are far less reliable for determining fatness in individuals."<ref>{{cite web | vauthors = Brody JE | date = 31 August 2010 |url=https://www.nytimes.com/2010/08/31/health/31brod.html|title=Weight Index Doesn't Tell the Whole Truth|work=[[The New York Times]] |url-status=live| archive-url=https://web.archive.org/web/20170501153306/http://www.nytimes.com/2010/08/31/health/31brod.html |archive-date=1 May 2017}}</ref>

For US adults, exponent estimates range from 1.92 to 1.96 for males and from 1.45 to 1.95 for females.<ref>{{cite journal | title = Weight-height relationships and body mass index: some observations from the Diverse Populations Collaboration | journal = American Journal of Physical Anthropology | volume = 128 | issue = 1 | pages = 220–229 | date = September 2005 | pmid = 15761809 | doi = 10.1002/ajpa.20107 | author1 = Diverse Populations Collaborative Group }}</ref><ref>{{cite journal | vauthors = Levitt DG, Heymsfield SB, Pierson RN, Shapses SA, Kral JG | title = Physiological models of body composition and human obesity | journal = Nutrition & Metabolism | volume = 4 | pages = 19 | date = September 2007 | pmid = 17883858 | pmc = 2082278 | doi = 10.1186/1743-7075-4-19 | doi-access = free }}</ref>

===Physical characteristics===
The BMI overestimates roughly 10% for a large (or tall) frame and underestimates roughly 10% for a smaller frame (short stature). In other words, people with small frames would be carrying more fat than optimal, but their BMI indicates that they are ''normal''. Conversely, large framed (or tall) individuals may be quite healthy, with a fairly low [[body fat percentage]], but be classified as ''overweight'' by BMI.<ref>{{cite web|url=http://www.medicalnewstoday.com/articles/265215.php|title=Why BMI is inaccurate and misleading|work=Medical News Today|date=25 August 2013|url-status=live|archive-url=https://web.archive.org/web/20150723131349/http://www.medicalnewstoday.com/articles/265215.php|archive-date=2015-07-23}}</ref>

For example, a height/weight chart may say the ideal weight (BMI 21.5) for a {{convert|5|ft|10|in|m|order=flip|adj=mid|-tall}} man is {{convert|150|lb|kg|order=flip}}. But if that man has a slender build (small frame), he may be overweight at {{cvt|150|lb|kg|disp=or|order=flip}} and should reduce by 10% to roughly {{cvt|135|lb|kg|disp=or|order=flip}} (BMI 19.4). In the reverse, the man with a larger frame and more solid build should increase by 10%, to roughly {{cvt|165|lb|kg|disp=or|order=flip}} (BMI 23.7). If one teeters on the edge of small/medium or medium/large, common sense should be used in calculating one's ideal weight. However, falling into one's ideal weight range for height and build is still not as accurate in determining health risk factors as [[waist-to-height ratio]] and actual body fat percentage.<ref>{{cite web|url=http://www.medicalnewstoday.com/articles/255712.php|title=BMI: is the body mass index formula flawed?|work=Medical News Today|url-status=live|archive-url=https://web.archive.org/web/20150723095030/http://www.medicalnewstoday.com/articles/255712.php|archive-date=2015-07-23}}</ref>

Accurate frame size calculators use several measurements (wrist circumference, elbow width, neck circumference, and others) to determine what category an individual falls into for a given height.<ref>{{cite web | vauthors = Lewis T| date = 22 August 2013 |url=http://www.livescience.com/39097-bmi-not-accurate-health-measure.html|title=BMI Not a Good Measure of Healthy Body Weight, Researchers Argue |work=LiveScience.com |url-status=live |archive-url= https://web.archive.org/web/20150721123646/http://www.livescience.com/39097-bmi-not-accurate-health-measure.html |archive-date=2015-07-21 }}</ref> The BMI also fails to take into account loss of height through ageing. In this situation, BMI will increase without any corresponding increase in weight.

===Muscle versus fat===
Assumptions about the distribution between muscle mass and fat mass are inexact. BMI generally overestimates [[adipose tissue|adiposity]] on those with leaner body mass (e.g., athletes) and underestimates excess adiposity on those with fattier body mass.

A study in June 2008 by Romero-Corral et al. examined 13,601 subjects from the United States' third [[National Health and Nutrition Examination Survey]] (NHANES III) and found that BMI-defined obesity (BMI ≥ 30) was present in 21% of men and 31% of women. Body fat-defined obesity was found in 50% of men and 62% of women. While BMI-defined obesity showed high [[Sensitivity and specificity|specificity]] (95% for men and 99% for women), BMI showed poor [[Sensitivity and specificity|sensitivity]] (36% for men and 49% for women). In other words, the BMI will be mostly correct when determining a person to be obese, but can err quite frequently when determining a person not to be. Despite this undercounting of obesity by BMI, BMI values in the intermediate BMI range of 20–30 were found to be associated with a wide range of body fat percentages. For men with a BMI of 25, about 20% have a body fat percentage below 20% and about 10% have body fat percentage above 30%.<ref name="RomeroCorral2008"/>

Body composition for athletes is often better calculated using measures of body fat, as determined by such techniques as skinfold measurements or underwater weighing and the limitations of manual measurement have also led to alternative methods to measure obesity, such as the [[Classification of obesity#Body Volume Index|body volume indicator]].<ref>{{Cite journal |last1=Tahrani |first1=Abd |last2=Boelaert |first2=Kristien |last3=Barnes |first3=Richard |last4=Palin |first4=Suzanne |last5=Field |first5=Annmarie |last6=Redmayne |first6=Helen |last7=Aytok |first7=Lisa |last8=Rahim |first8=Asad |date=2008-04-01 |title=Body volume index: time to replace body mass index? |url=https://www.endocrine-abstracts.org/ea/0015/ea0015p104 |journal=Endocrine Abstracts |language=en |volume=15 |issn=1470-3947}}</ref>

===Variation in definitions of categories===
It is not clear where on the BMI scale the threshold for ''[[overweight]]'' and ''[[obesity|obese]]'' should be set. Because of this, the standards have varied over the past few decades. Between 1980 and 2000 the U.S. Dietary Guidelines have defined overweight at a variety of levels ranging from a BMI of 24.9 to 27.1. In 1985, the [[National Institutes of Health]] (NIH) consensus conference recommended that overweight BMI be set at a BMI of 27.8 for men and 27.3 for women.

In 1998, an NIH report concluded that a BMI over 25 is overweight and a BMI over 30 is obese.<ref name = "CNN_1998" /> In the 1990s the [[World Health Organization]] (WHO) decided that a BMI of 25 to 30 should be considered overweight and a BMI over 30 is obese, the standards the NIH set. This became the definitive guide for determining if someone is overweight.

One study found that the vast majority of people labelled 'overweight' and 'obese' according to current definitions do not in fact face any meaningful increased risk for early death. In a quantitative analysis of several studies, involving more than 600,000 men and women, the lowest mortality rates were found for people with BMIs between 23 and 29; most of the 25–30 range considered 'overweight' was not associated with higher risk.<ref>{{cite journal | vauthors = Campos P, Saguy A, Ernsberger P, Oliver E, Gaesser G | title = The epidemiology of overweight and obesity: public health crisis or moral panic? | journal = International Journal of Epidemiology | volume = 35 | issue = 1 | pages = 55–60 | date = February 2006 | pmid =  16339599| doi = 10.1093/ije/dyi254 | doi-access =  }}</ref>

==Alternatives==

===Corpulence index (exponent of 3)===
The [[corpulence index]] uses an exponent of 3 rather than 2. The corpulence index yields valid results even for very short and very tall people,<ref>{{Cite book |last=Ditmier |first=Lawrence F. |title=New Developments in Obesity Research |publisher=Nova Science Publishers |year=2006 |isbn=1-60021-296-4 |location=Hauppauge, New York}}{{page needed|date=April 2012}}</ref> which is a problem with BMI. For example, a {{convert|152.4|cm|ftin|abbr=on}} tall person at an ideal body weight of {{convert|48|kg|lb|abbr=on}} gives a normal BMI of 20.74 and CI of 13.6, while a {{convert|200|cm|ftin|abbr=on}} tall person with a weight of {{convert|100|kg|lb|abbr=on}} gives a BMI of 24.84, very close to an overweight BMI of 25, and a CI of 12.4, very close to a normal CI of 12.<ref>{{Cite journal|title=Taller people should have Higher BMI's and Blood Pressure Measurements as their Normal|url=https://biomedres.us/pdfs/BJSTR.MS.ID.001381.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://biomedres.us/pdfs/BJSTR.MS.ID.001381.pdf |archive-date=2022-10-09 |url-status=live|journal=Biomed J Sci & Tech Res|year=2018|doi=10.26717/BJSTR.2018.06.001381|doi-access=free|last1=v Roth|first1=Jonathan|volume=6|issue=4}}</ref>

===New BMI (exponent of 2.5)===
A study found that the best exponent E for predicting the fat percent would be between 2 and 2.5 in <math>\text{mass}/\text{height}^E</math>.<ref>{{cite journal |url=https://www.sciencedirect.com/science/article/pii/S0002916523274547 |title=Scaling of human body composition to stature: new insights into body mass index |author=Heymsfield Steven B, Gallagher Dympna, Mayer Laurel, Beetsch Joel ja Pietrobelli Angelo|volume=86 |issue=1 |date=July 2007 |pages=82–91 |journal=The American Journal of Clinical Nutrition|doi=10.1093/ajcn/86.1.82 |pmid=17616766 |pmc=2729090 }}</ref> 

An exponent of 5/2 or 2.5 was proposed by Quetelet in the 19th century:<ref name=":0">Quetelet A. A Treatise on Man and the Development of his Faculties</ref>
<blockquote>In general, we do not err much when we assume that during development the squares of the weight at different ages are as the fifth powers of the height</blockquote>

This exponent of 2.5 is used in a revised formula for Body Mass Index, proposed by [[Nick Trefethen]], Professor of numerical analysis at the [[University of Oxford]],<ref name = "Trefethen">{{cite web| vauthors = Trefethen N |title=New BMI (Body Mass Index)|url=https://people.maths.ox.ac.uk/trefethen/bmi.html|website=Ox.ac.uk|publisher=Mathematical Institute, [[University of Oxford]]|access-date=5 February 2019}}</ref> which minimizes the distortions for shorter and taller individuals resulting from the use of an exponent of 2 in the traditional BMI formula:

<math display="block">\mathrm{BMI}_\text{new} = 1.3 \times \frac{\text{mass}_\text{kg}}{\text{height}_\text{m}^{2.5}}</math>

The scaling factor of 1.3 was determined to make the proposed new BMI formula align with the traditional BMI formula for adults of average height, while the exponent of 2.5 is a compromise between the exponent of 2 in the traditional formula for BMI and the exponent of 3 that would be expected for the scaling of weight (which at constant density would theoretically scale with volume, i.e., as the cube of the height) with height. In Trefethen's analysis, an exponent of 2.5 was found to fit empirical data more closely with less distortion than either an exponent of 2 or 3.

===BMI prime (exponent of 2, normalization factor)===
BMI Prime, a modification of the BMI system, is the ratio of actual BMI to upper limit optimal BMI (currently defined at 25&nbsp;kg/m<sup>2</sup>), i.e., the actual BMI expressed as a proportion of upper limit optimal. BMI Prime is a [[dimensionless number]] independent of units. Individuals with BMI Prime less than 0.74 are underweight; those with between 0.74 and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI Prime is useful clinically because it shows by what ratio (e.g. 1.36) or percentage (e.g. 136%, or 36% above) a person deviates from the maximum optimal BMI.

For instance, a person with BMI 34&nbsp;kg/m<sup>2</sup> has a BMI Prime of 34/25 = 1.36, and is 36% over their upper mass limit. In South East Asian and South Chinese populations (see [[#International variations|§ international variations]]), BMI Prime should be calculated using an upper limit BMI of 23 in the denominator instead of 25. BMI Prime allows easy comparison between populations whose upper-limit optimal BMI values differ.<ref>{{cite journal | vauthors = Gadzik J | title = 'How much should I weigh?'--Quetelet's equation, upper weight limits, and BMI prime | journal = Connecticut Medicine | volume = 70 | issue = 2 | pages = 81–88 | date = February 2006 | pmid = 16768059 }}</ref>

===Waist circumference===
{{Main|Waist-to-height ratio|Waist-to-hip ratio}}
Waist circumference is a good indicator of [[visceral fat]], which poses more health risks than fat elsewhere. According to the U.S. [[National Institutes of Health]] (NIH), waist circumference in excess of {{cvt|1020|mm}} for men and {{cvt|880|mm}} for (non-pregnant) women is considered to imply a high risk for type 2 diabetes, [[dyslipidemia]], [[hypertension]], and [[cardiovascular disease]] CVD. Waist circumference can be a better indicator of obesity-related disease risk than BMI. For example, this is the case in populations of Asian descent and older people.<ref>{{cite web |title=Obesity Education Initiative Electronic Textbook – Treatment Guidelines |url=http://www.nhlbi.nih.gov/health-pro/guidelines/current/obesity-guidelines/e_textbook/txgd/4142.htm |url-status=live |archive-url=https://web.archive.org/web/20170501084223/https://www.nhlbi.nih.gov/health-pro/guidelines/current/obesity-guidelines/e_textbook/txgd/4142.htm |archive-date=1 May 2017 |access-date=29 July 2016 |website=US National Institutes of Health}}</ref> {{cvt|940|mm}} for men and {{cvt|800|mm}} for women has been stated to pose "higher risk", with the NIH figures "even higher".<ref>{{cite web|url=http://www.nhs.uk/chq/Pages/849.aspx?CategoryID=51|title=Why is my waist size important?|website=UK HNS Choices|access-date=29 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160806210351/http://www.nhs.uk/chq/Pages/849.aspx?CategoryID=51|archive-date=6 August 2016}}</ref>

Waist-to-hip circumference ratio has also been used, but has been found to be no better than waist circumference alone, and more complicated to measure.<ref>{{cite web|url=https://www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/abdominal-obesity/|title=Waist Size Matters|website=Harvard School of Public Health|date=2012-10-21|access-date=29 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160821092935/https://www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/abdominal-obesity/|archive-date=21 August 2016}}</ref>

A related indicator is waist circumference divided by height. A 2013 study identified critical threshold values for [[waist-to-height ratio]] according to age, with consequent significant reduction in life expectancy if exceeded. These are: 0.5 for people under 40 years of age, 0.5 to 0.6 for people aged 40–50, and 0.6 for people over 50 years of age.<ref>{{cite web | author = HospiMedica International staff writers |url=http://www.hospimedica.com/critical-care/articles/294746805/waist-height-ratio-better-than-bmi-for-gauging-mortality.html |title=Waist-Height Ratio Better Than BMI for Gauging Mortality |date=18 Jun 2013 |access-date=7 April 2016 |url-status=live |archive-url=https://web.archive.org/web/20160417064352/http://www.hospimedica.com/critical-care/articles/294746805/waist-height-ratio-better-than-bmi-for-gauging-mortality.html |archive-date=17 April 2016 }}</ref>

=== Surface-based body shape index ===
The Surface-based Body Shape Index (SBSI) is far more rigorous and is based upon four key measurements: the [[body surface area]] (BSA), vertical trunk circumference (VTC), waist circumference (WC) and height (H). Data on 11,808 subjects from the National Health and Human Nutrition Examination Surveys (NHANES) 1999–2004, showed that SBSI outperformed BMI, waist circumference, and [[Body Shape Index|A Body Shape Index]] (ABSI), an alternative to BMI.<ref>{{Cite web | vauthors = Pomeroy R | date = 29 December 2015 |title = A New Potential Replacement for Body Mass Index {{!}} RealClearScience|url = http://www.realclearscience.com/journal_club/2015/12/30/a_new_potential_replacement_for_body_mass_index_109492.html|website = realclearscience.com|access-date = 2015-12-31|url-status=live|archive-url = https://web.archive.org/web/20160101113606/http://www.realclearscience.com/journal_club/2015/12/30/a_new_potential_replacement_for_body_mass_index_109492.html|archive-date = 2016-01-01}}</ref><ref name="rahman2015">{{cite journal | vauthors = Rahman SA, Adjeroh D | title = Surface-Based Body Shape Index and Its Relationship with All-Cause Mortality | journal = PLOS ONE | volume = 10 | issue = 12 | pages = e0144639 | year = 2015 | pmid = 26709925 | pmc = 4692532 | doi = 10.1371/journal.pone.0144639 | bibcode = 2015PLoSO..1044639R | doi-access = free }}</ref>

<math display="block">\mathrm{SBSI} = \frac{(\text{H}^{7/4})(\text{WC}^{5/6})}{\text{BSA VTC}}</math>

A simplified, dimensionless form of SBSI, known as SBSI<sup>*</sup>, has also been developed.<ref name="rahman2015" />

<math display="block">\mathrm{SBSI^\star} = \frac{(\text{H}^2)(\text{WC})}{\text{BSA VTC}}</math>

===Modified body mass index===
Within some medical contexts, such as [[familial amyloid polyneuropathy]], serum albumin is factored in to produce a modified body mass index (mBMI). The mBMI can be obtained by multiplying the BMI by [[human serum albumin|serum albumin]], in grams per litre.<ref>{{cite journal|vauthors=Tsuchiya A, Yazaki M, Kametani F, Takei Y, Ikeda S|date=April 2008|title=Marked regression of abdominal fat amyloid in patients with familial amyloid polyneuropathy during long-term follow-up after liver transplantation|journal=Liver Transplantation|volume=14|issue=4|pages=563–570|doi=10.1002/lt.21395|pmid=18383093|doi-access=|s2cid=13072583}}</ref>

== See also ==
<!-- Please keep entries in alphabetical order & add a short description per [[WP:SEEALSO]] -->
* [[Allometry]]
* [[Body roundness index]]
* [[Body water]]
* [[History of anthropometry]]
* [[List of countries by body mass index]]
* [[Normal weight obesity]]
* [[Obesity paradox]]
* [[Relative Fat Mass]]
* [[Somatotype and constitutional psychology]]
<!-- please keep entries in alphabetical order -->

== Explanatory notes ==
{{Notelist|30em|refs=
* {{efn|name="range-precision"|After rounding.}}
}}

== References ==
{{Reflist|30em}}

== Further reading ==
{{Refbegin}}
* {{Cite book | veditors = Ferrera LA |year=2006 |title=Focus on Body Mass Index And Health Research |location=New York |publisher=Nova Science |isbn=978-1-59454-963-2}}
* {{Cite book | veditors = Samaras TT |year=2007 |title=Human Body Size and the Laws of Scaling: Physiological, Performance, Growth, Longevity and Ecological Ramifications |location=New York |publisher=Nova Science |isbn=978-1-60021-408-0}}
* {{Cite book | veditors = Sothern MS, Gordon ST, von Almen TK |date=19 April 2016 |title=Handbook of Pediatric Obesity: Clinical Management |edition=Illustrated |publisher=CRC Press |isbn=978-1-4200-1911-7}}
{{Refend}}

== External links ==
{{Commons category}}
{{Wiktionary|body mass index}}
<!-- Please do not add more links to more calculators. If you feel a particular online calculator has specific merits, please propose the link on the talk page. -->
* U.S. National Center for Health Statistics:
** [https://www.cdc.gov/growthcharts/ BMI Growth Charts for children and young adults]
** [https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/english_bmi_calculator/bmi_calculator.html  BMI calculator ages 20 and older]

{{Authority control}}

{{DEFAULTSORT:Body mass index}}
[[Category:Belgian inventions]]
[[Category:Body shape]]
[[Category:Classification of obesity]]
[[Category:Human body weight]]
[[Category:Human height]]
[[Category:Mathematics in medicine]]
[[Category:Medical signs]]
[[Category:Ratios]]