The body mass index (BMI) is the standard and most commonly-used method for assessing body weight by health professionals. It is calculated by dividing an individual's weight in kg by the square of their height in meters. The fact that some arithmetic is required to ascertain the BMI makes it look quite scientific and robust. The fact of the matter is that it tells us nothing about body composition or the distribution of fat in the body. Oh, and there's another problem with the BMI: individuals in the "overweight" category (BMI 25-29.9) seem to enjoy at least as good overall health if not better than those in the "healthy" category.
As a measurement of health status as it is currently applied the BMI is a misleading waste of time. The good news is that there are other more easily determined and more useful measurements out there. One of these is the circumference of the waist. Basically, the bigger this is, the more fat is likely to be congregated around the abdomen, and it is this sort of fat that seems to be most strongly associated with chronic diseases, such as heart disease and type 2 diabetes. In short, the thought is that the bigger one's belly, the more likely one is to get sick and die.
In a recent study published in the American Journal of Epidemiology, the relationship between waist circumference and overall risk of death was assessed in almost 250,000 men and women over a nine-year period [1]. As part of the study, the researchers isolated individuals who from a BMI perspective were "healthy" in terms of weight (BMI 18.5–24.9). In this group, the overall risk of death in those with considered to have large waist circumferences (for men a waist size of 40 inches or greater and for women a waist size of 34.5 inches or greater) was compared to those with individuals of normal waist circumferences (measurements less than the above). The results of this study were: Men with the higher waist circumferences were found to have a 23 percent increased risk of death. Women with the higher waist circumferences were found to have a 22 percent increased risk of death.
These findings serve to highlight the importance of waist size as a measure of health status. They also serve to highlight the inadequacy of the BMI as a tool or assessing risk of chronic disease and death.
For those wishing to trim their waists, my suggestion is to consider a diet lower in the carbohydrates that tend to destabilize blood sugar and insulin levels. The rationale here is that abdominal obesity is often a feature of metabolic syndrome, in which elevated levels of insulin and/or insulin resistance are usually features. It can be that a glut of carbohydrate in the diet can cause insulin surges, which predispose to fat deposition around the abdomen. So, one obvious approach to this problem is to cut back on carbs.
I recently reported on a study of a low-carb "primal" diet that was found to be effective for weight loss and diminishing waist circumference. The study has some deficiencies, but it did mirror what I almost invariably find to work in practice for the purposes of waist reduction.
Reference:
[1] American Journal of Epidemiology: Waist Circumference and Mortality 2008 167(12): 1465-1475; doi: 10.1093/aje/kwn079
Dr. John Briffa is a London-based doctor and author with an interest in nutrition and natural medicine.
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