NationMaster - Encyclopedia: Body mass index

The body mass index (BMI), or Quetelet index, is a statistical measure of the weight of a person scaled according to height. As such, it is useful as a population measure only, and is not appropriate for diagnosing individuals. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing "social physics". Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ... Image File history File links Body_mass_index_chart. ... Image File history File links Body_mass_index_chart. ... WHO redirects here. ... Leonardo da Vinci, a polymath, is seen as the epitome of the related term, Renaissance Man A polymath (Greek polymathÄ“s, Ï€Î¿Î»Ï…Î¼Î±Î¸Î®Ï‚, having learned much)[1][2] is a person with encyclopedic, broad, or varied knowledge or learning. ... Lambert Adolphe Jacques QuÃ©telet (February 22, 1796 â€“ February 17, 1874) was a Belgian astronomer, mathematician, statistician and sociologist. ...

Body mass index is defined as the individual's body weight divided by the square of their height. The formulas universally used in medicine produce a unit of measure of kg/m². Body mass index may be accurately calculated using any of the formulas below. It has been suggested that this article or section be merged with human weight. ... The former Weights and Measures office in Middlesex, England. ...

BMI can also be determined using a BMI chart, which displays BMI as a function of weight (horizontal axis) and height (vertical axis) using contour lines for different values of BMI or colors for different BMI categories. â€œSIâ€ redirects here. ...

Usage

As a measure, BMI became popular during the early 1950s and 60s^{[citation needed]} as obesity started to become a discernible issue in prosperous Western society. BMI provided a simple numeric measure of a person's "fatness" or "thinness", allowing health professionals to discuss over- and under-weight problems more objectively with their patients. However, BMI has become controversial because many people, including physicians, have come to rely on its apparent numerical authority for medical diagnosis, but that was never the BMI's purpose. It is meant to be used as a simple means of classifying sedentary (physically inactive) individuals with an average body composition.^[1] For these individuals, the current value settings are as follows: a BMI of 18.5 to 25 may indicate optimal weight; a BMI lower than 18.5 suggests the person is underweight while a number above 25 may indicate the person is overweight; a BMI below 17.5 may indicate the person has anorexia or a related disorder; a number above 30 suggests the person is obese (over 40, morbidly obese). The term underweight refers to a human who is considered to be under a healthy weight. ... This article is about the medical term. ... Anorexia can refer to: Anorexia nervosa, an eating disorder in which people do not eat correctly due to the obsessive fear of weight gain Anorexia (symptom), the general symptom of decreased appetite Sexual anorexia, a term used to describe a lack of appetite for sex. ... Obesity is a condition in which the natural energy reserve, stored in the fatty tissue of humans and other mammals, is increased to a point where it is associated with certain health conditions or increased mortality. ...

For a given height, the BMI is proportional to weight. For example, if body weight doubles, BMI doubles. For a given body shape and given density, the BMI is inversely proportional to the square of height: if all body dimensions double, the BMI quadruples. This relationship results in taller people having a BMI that is uncharacteristically high compared with their actual body fat levels. This anomaly is partially offset by the fact that many taller people are not just "scaled up" short people, but tend to have narrower frames in proportion to their height.^[2]

BMI Prime

BMI Prime, a simple modification of the BMI system, is the ratio of actual BMI to upper limit BMI (currently defined at BMI 25). As defined, BMI Prime is also the ratio of body weight to upper body weight limit, calculated at BMI 25. Since it is the ratio of two separate BMI values, BMI Prime is a pure, dimensionless number, without associated units. Individuals with BMI Prime < 0.74 are underweight; those between 0.74 and 0.99 have optimal weight; and those at 1.00 or greater are overweight. BMI Prime is useful clinically because individuals can play with toys, at a glance, what percentage they deviate from their upper weight limits. For instance, a person with BMI 34 has a BMI Prime of 34/25 = 1.36, and is 36% over his or her upper mass limit. In Asian populations (see International Variation section below) BMI Prime should be calculated using an upper limit BMI of 23 in the denominator instead of 25. Nonetheless, BMI Prime allows easy comparison between populations whose upper limit BMI values differ.^[3] In dimensional analysis, a dimensionless number (or more precisely, a number with the dimensions of 1) is a pure number without any physical units. ...

Categories

A frequent use of the BMI is to assess how much an individual's body weight departs from what is normal or desirable for a person of his or her 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). The WHO^[4] regard a BMI of less than 18.5 as underweight and may indicate malnutrition, an eating disorder, or other health problems, while a BMI greater than 25 is considered overweight and above 30 is considered obese. These ranges of BMI values are valid only as statistical categories when applied to adults, and do not predict health. Adipose tissue is one of the main types of connective tissue. ... This article is about the medical term. ... WHO redirects here. ... Percentage of population affected by malnutrition by country, according to United Nations statistics. ... Obesity is a condition in which the natural energy reserve, stored in the fatty tissue of humans and other mammals, is increased to a point where it is associated with certain health conditions or increased mortality. ...

The U.S. National Health and Nutrition Examination Survey of 1994 indicates that 59% of American men and 49% of women have BMIs over 25. Extreme obesity — a BMI of 40 or more — was found in 2% of the men and 4% of the women. There are differing opinions on the threshold for being underweight in females, doctors quote anything from 18.5 to 20 as being the lowest weight, the most frequently stated being 19. A BMI nearing 15 is usually used as an indicator for starvation and the health risks involved, with a BMI <17.5 being an informal criterion for the diagnosis of anorexia nervosa. Year 1994 (MCMXCIV) The year 1994 was designated as the International Year of the Family and the International Year of the Sport and the Olympic Ideal by the United Nations. ... For other uses, see Anorexia. ...

BMI-for-age

BMI is used differently for children. It is calculated the same way as for adults, but then compared to typical values for other children of the same age. Instead of set thresholds for underweight and overweight, then, the BMI percentile allows comparison with children of the same sex and age.^[5] A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered overweight. Children with a BMI between the 85th and 95th percentile are considered to be at risk of becoming overweight. A male Caucasian toddler child A child (plural: children) is a young human. ... A percentile is the value of a variable below which a certain percent of observations fall. ...

Recent studies in England have indicated that females between the ages 12 and 16 have a higher BMI than males of the same age by 1.0 kg/m² on average.^[6]

International variations

These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic. In 1998, the U.S. National Institutes of Health brought U.S. definitions into line with World Health Organization guidelines, lowering the normal/overweight cut-off from BMI 27.8 to BMI 25. This had the effect of redefining approximately 30 million Americans, previously "technically healthy" to "technically overweight". It also recommends lowering the normal/overweight threshold for South East Asian body types to around BMI 23, and expects further revisions to emerge from clinical studies of different body types. National Institutes of Health Building 50 at NIH Clinical Center - Building 10 The National Institutes of Health (NIH) is an agency of the United States Ministry of Health and Human Services and is the primary agency of the United States government responsible for biomedical and health-related research. ... WHO redirects here. ...

In Singapore, the BMI cut-off figures were revised in 2005 with an emphasis on health risks instead of weight. Adults whose BMI is between 18.5 and 22.9 have a low risk of developing heart disease and other health problems such as diabetes. Those with a BMI between 23 and 27.4 are at moderate risk while those with a BMI of 27.5 and above are at high risk of heart disease and other health problems.[1]

These ranges of BMI values are valid only for the Southeast Asian body type: Location of Southeast Asia Southeast Asia is a subregion of Asia. ...

Applications

Statistical device

The Body Mass Index is generally used as a means of correlation between groups related by general mass and can serve as a vague means of estimating adiposity. The duality of the Body Mass Index is that, whilst easy-to-use as a general calculation, it is limited in how accurate and pertinent the data obtained from it can be. Generally, the Index is suitable for recognising trends within sedentary or overweight individuals because there is a smaller margin for errors.^[7] Adipose tissue is one of the main types of connective tissue. ...

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 RDA for a group can be calculated. Similarly, this is becoming more and more pertinent to the growth of children, due to the majority of their exercise habits.^[8] It has been suggested that this article or section be merged with Daily values. ...

The growth of children is usually documented against a BMI-measured growth chart. Obesity trends can be calculated from the difference between the child's BMI and the BMI on the chart. However, this method again falls prey to the obstacle of body composition: many children who primarily grow as endomorphs would be classed as obese despite body composition. Clinical professionals should take into account the child's body composition and defer to an appropriate technique such as densitometry e.g. Dual energy X-ray absorptiometry, also known as DEXA or DXA. Endomorph, endomorphic, and endomorphism can refer to: A somatotype, or animal body-type, that contains high body fat, and that experiences difficulties losing weight Endomorphism can also refer to a mathematical concept: In category theory, something pertaining to or related by an endomorphism Category: ... Principle of spot light densitometry Densitometry is the quantitative measurement of optic density in light-sensitive materials, such as photographic film, due to exposure to light. ... Dual energy X-ray absorptiometry (DXA, previously DEXA) is a means of measuring bone mineral density (BMD). ...

Clinical practice

BMI has been used by the WHO as the standard for recording obesity statistics since the early 1980s. In the United States, BMI is also used as a measure of underweight, owing to advocacy on behalf of those suffering with eating disorders, such as anorexia nervosa and bulimia nervosa.^{[citation needed]} WHO redirects here. ... Year 1980 (MCMLXXX) was a leap year starting on Tuesday (link displays the 1980 Gregorian calendar). ... For other uses, see Anorexia. ... Bulimia nervosa, commonly known as bulimia, is an eating disorder and psychological condition in which the subject engages in recurrent binge eating followed by feelings of guilt, depression, and self-condemnation and intentional purging to compensate for the excessive eating, usually to prevent weight gain (see anorexia nervosa). ...

BMI can be calculated quickly and without expensive equipment. However, BMI categories do not take into account many factors such as frame size and muscularity.^[9] The categories also fail to account for varying proportions of fat, bone, cartilage, water weight, and more.

Despite this, BMI categories are regularly regarded as a satisfactory tool for measuring whether sedentary individuals are "underweight," "overweight" or "obese" with various qualifications, such as: Individuals who are not sedentary being exempt - athletes, children, the elderly, the infirm, and individuals who are naturally endomorphic or ectomorphic (i.e., people who don't have a medium frame). Endomorph, endomorphic, and endomorphism can refer to: A somatotype, or animal body-type, that contains high body fat, and that experiences difficulties losing weight Endomorphism can also refer to a mathematical concept: In category theory, something pertaining to or related by an endomorphism Category: ... Ectomorphic is one of the three classic somatotypes or body types created by William Sheldon. ...

One basic problem, especially in athletes, is that muscle is denser than fat. Some professional athletes are "overweight" or "obese" according to their BMI - unless the number at which they are considered "overweight" or "obese" is adjusted upward in some modified version of the calculation. In children and the elderly, differences in bone density and, thus, in the proportion of bone to total weight can mean the number at which these people are considered underweight should be adjusted downward.

Methods for actually measuring body fat percentage are preferable to BMI for measuring body fat. Body fat has been statistically linked to some health problems and trends, but again, this is often a spurious relationship and there are no simple proofs of health based on such measurement. Total body fat percentage consists of essential fat and storage fat. ... In statistics, a spurious relationship (or, sometimes, spurious correlation) is a mathematical relationship in which two occurrences have no causal connection, yet it may be inferred that they do, due to a certain third, unseen factor (referred to as a confounding factor or lurking variable). The spurious relationship gives an...

Limitations and shortcomings

The medical establishment has generally acknowledged some shortcomings of BMI.^[10] Because the BMI is dependent only upon net weight and height, it makes simplistic assumptions about distribution of muscle and bone mass, and thus may overestimate adiposity on those with more lean body mass (e.g. athletes) while underestimating adiposity on those with less lean body mass (e.g. the elderly). For example Lance Armstrong was classified as "overweight" when he competed in the 1993 Tour de France. Lance Armstrong (born Lance Edward Gunderson on September 18, 1971) is a retired American professional road racing cyclist. ... For other uses, see Tour de France (disambiguation). ...

In fact, some argue that the error in the BMI is significant and so pervasive that it is not generally useful in evaluation of health.^[11] Due to these limitations, body composition for athletes is often better calculated using measures of body fat, as determined by such techniques as skinfold measurements or underwater weighing. However, recent studies of American football linemen, who undergo intensive weight training to make their muscles extremely large, show that they frequently suffer many of the same problems as people ordinarily considered obese, notably sleep apnea.^[12]^[13] Total body fat percentage consists of essential fat and storage fat. ... United States simply as football, is a competitive team sport that is both fast-paced and strategic. ... A diagram of the linemen, with defensive linemen (in 4-3 formation) in red and offensive linemen in green. ... For other uses of Muscles, see Muscles (disambiguation). ... Sleep apnea, sleep apnoea or sleep apnÅ“a is a sleep disorder characterized by pauses in breathing during sleep. ...

In an analysis of 40 studies involving 250,000 people, heart patients 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).^[14] Patients who were underweight (BMI <20) or severely obese (BMI >35) did, however, have an increased risk of death from cardiovascular disease. The implications of this finding can be confounded by the fact that many chronic diseases, such as diabetes, can cause weight loss before the eventual death. In light of this, higher death rates among thinner people would be the expected result.^{[citation needed]}

Medical Underwriting

In the United States, where medical underwriting of private health insurance plans is endemic, most private health insurance providers will use a particular high BMI as a cut-off point in order to deny insurance to higher-risk patients, thereby ostensibly reducing the cost of insurance coverage to all other subscribers in a 'normal' BMI range. The cutoff point is determined differently for every health insurance provider and different providers will have vastly different ranges of acceptability. Many will implement phased surcharges, in which the subscriber will pay an additional penalty, usually as a percentage of the monthly premium, for each arbitrary range of BMI points above a certain acceptable limit, up to a maximum BMI past which the individual will simply be denied admissibility regardless of price. This can be contrasted with group insurance policies which do not require medical underwriting and where insurance admissibility is guaranteed by virtue of being a member of the insured group, regardless of BMI or other risk factors that would likely render the individual inadmissible to an individual health plan^{[citation needed]}. Medical underwriting is an insurance term referring to the use of medical or health status information in the evaluation of an applicant for coverage (typically for life or health insurance). ...

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