Title of article:

Beyond body mass index.

Authors: Prentice AM, Jebb SA.
Journal: Obes Rev 2001 Aug;2(3):141-7

Abstract

Body mass index (BMI) is the cornerstone of the current classification system for obesity and its advantages are widely exploited across disciplines ranging from international surveillance to individual patient assessment. However, like all anthropometric measurements, it is only a surrogate measure of body fatness. Obesity is defined as an excess accumulation of body fat, and it is the amount of this excess fat that correlates with ill-health. We propose therefore that much greater attention should be paid to the development of databases and standards based on the direct measurement of body fat in populations, rather than on surrogate measures. In support of this argument we illustrate a wide range of conditions in which surrogate anthropometric measures (especially BMI) provide misleading information about body fat content. These include: infancy and childhood; ageing; racial differences; athletes; military and civil forces personnel; weight loss with and without exercise; physical training; and special clinical circumstances. We argue that BMI continues to serve well for many purposes, but that the time is now right to initiate a gradual evolution beyond BMI towards standards based on actual measurements of body fat mass.

Comments and Key points

To summarize this article's criticisms of Body Mass Index as a classifier of obesity:

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.

References

1. 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.
2. The Asia-Pacific Perspective: Redefining obesity and its treatment. Health Communications Australia Pty Ltd: Syndey, 2000.

Review & comments by Steven B. Halls, MD, Edited most recently on 23-June, 2008, Copyright.
See the other Body Mass Index readings.