Comments and body mass index review
1. Aging. With aging, body fat increases and muscle diminishes. Body weight and Body Mass index can stay stable during these changes.
This chart comes from Cohn1, illustrating that body weight (and BMI) were stable, while fat increased during aging. It doesn’t answer the question, is this "natural" or "disease"? One shouldn’t assume it is unnatural without evidence.
2. Race & Nationality. This article gives several examples of non-white non-American races, that have a higher body fat percentage for a given BMI. This supports the conclusion that different races need different BMI overweight thresholds. For example, Asians range of normal BMI is lower, between 18.5 to 22.9 kg/m2, with BMI>=23.0 is considered overweight for Asians2. Black Americans probably need a higher BMI cutoff.
3. Athletes & Bodybuilders. This article cites a nice example of professional football players and olympic shot-putters, with overweight and obese BMI’s (apparently), but actually having low body fat percentages. It is their greater muscle mass that elevates their body mass index.
4. Adolescents. The BMI standards for adolescents assume an average degree of maturation. But it is well known that some adolescents go through puberty early, some later than average, and it makes a big difference.
- Cohn SH. New concepts of body composition. In: Ellis KJ, Yasumura S, Morgan WD (eds). In Vivo Body Composition studies. The Institute of Physical Sciences in medicine: London, 1987, pp1-14.
- The Asia-Pacific Perspective: Redefining obesity and its treatment. Health Communications Australia Pty Ltd: Syndey, 2000.
- Mascie-Taylor CG, Goto R, Human variation and body mass index: a review of the universality of BMI cut-offs, gender and urban-rural differences and secular changes. J Physiol Anthropol 2007; 26:109-12