Body Mass Index or BMI is a good estimate of fatness for most adults. It is measured as the body mass divided by the square of the body height. It is expressed in kg/m2.
The transition cutoffs for normal weight to overweight and overweight to obese weight are 25 and 30, respectively. Most diet planning is done based on these numbers. However, over the last 20 years, evidence is gathering that some ethnicities such as Asians have a much higher genetic tendency to develop metabolic syndrome. As a result, they develop diabetes and other health conditions at much lower BMIs compared to the white-skinned people.
When studied further, the similar transition cutoffs for normal weight to overweight and overweight to obese weight are found to be 22 and 27, respectively in the Asian population.
- BMI is a good tool for population measures but not very appropriate for individual decisions. One can have higher weight due to excess fat or muscle mass. While the latter is good for health, the person can get tagged into overweight category.
- Lower BMI is not necessarily good beyond a certain level. People with low BMI could have some medical disorder such as cancer, tuberculosis, or sarcopenia, which can cause muscle atrophy and loss of weight.
- The average BMI of athletes is 22.4 for women and 23.6 for men.
- In real life, body mass does not scale with height2. It scales with height2.5. So a new body mass index is proposed, which is defined as BMInew = 1.3 × body masskg/ body heightm2.5
- For deciding BMI cutoffs for overweight and obese weight, the scientists plotted BMI on x-axis and incidence of diseases such as diabetes and heart diseases on y-axis. At certain inflection points, the disease incidence went up sharply. Those BMI values were taken as the cutoffs for overweight and obese weight, respectively.
- When the original BMI cutoffs were decided, the scientists had selected only white-skinned caucasians in the study. So those levels of 25 and 30 for overweight and obesity, respectively applied only for white-skinned people.
- When the similar exercise was done for asians, the equivalent levels were found to be 22 and 27, respectively.
- The World Health Organisation (WHO) refused to accept these data and research papers for many years. Eventually, individual countries started modifying their own guidelines. After a few years, the WHO accepted the proposition and now, many medical associations give ethnicity-specific guidelines.
- Japan and China consider the cutoffs to be 24 and 28, respectively. In India, the cutoffs of 23 and 27 are slowly getting accepted.
- A better indicator of individual health is abdominal obesity.
- A healthy BMI indicates a good health status; it has nothing to do with looking good. In fact, many people including me look scrawny at the BMI of 22. Being healthier is different from being healthier-looking. Choose your poison!
To Read More
- Harvard University: Ethnic Differences in BMI and Disease Risk
- Wikipedia: Body Mass Index
- Research Paper: Ethnic-Specific Criteria for Classification of Body Mass Index: Asian Indians and ADA Position Statement
First published on: 11th December 2021
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