Dr. Tim Says....

Weighing In: Body Mass Index as a Guide to Your Health

In a recent News Bite I discussed the importance of different types of research studies. Prospective studies are especially important because research that is designed to follow people over time is more accurate than the retrospective study where participants are asked to recall diet histories.

The two other types of research are defined as either observational (where no particular change is made to a person’s lifestyle) or interventional (where those being studied are asked to follow a new diet plan). Observational studies allow us to evaluate what issues might exist that best promote health while interventional research studies which changes work best.

In a large prospective, observational study Kenneth F. Adams and his colleagues mailed questionnaires to a group of AARP members (NEJM 2006; 355: 763-778). Over a half million people responded and supplied information about themselves including height, weight, age, gender, ethnic origin, disease history, smoking habits, physical activity and diet.

There is clear research prior to this study showing that those with a Body Mass Index (BMI) over 30.0 are at much higher risk of disease and death. Dr. Adams’ study once again confirms those previous findings. Interestingly, when the researchers looked at those who were overweight (BMI between 25.0 and 30.0) they found only a weak association with increased death in women (but not in men).

Dr. Adams and his colleagues also evaluated those participants who had never smoked at all. They found that the risk of death was increased both for those who were overweight as well as for those who were obese. By eliminating the smokers, the researchers unmasked this important health issue for people with a BMI between 25.0 and 30.0.

A supplementary questionnaire asking participants about their height and weight at age 50 revealed an even stronger association with being overweight and an increase in death by 20% to 40% (again in the subgroup of non-smokers). A study in 1999 by the American Cancer Society found similar results.

This research has quickly resulted in a great deal of debate mostly from those who feel that BMI is not the optimum research tool. The argument is that one can have a BMI of 27 and still be very healthy because the important factor is the percentage of one’s body fat. I agree with such criticism, but at the same time I feel that such critics miss the big picture. As with research, BMI should be used a guide for us and should be treated as such.

In my practice I now measure BMI and Waist to Hip Ratio (WHR) as well as a waist circumference. These three measures together can provide a pretty good guide of where one’s health stands and can help clarify your risk of disease. Check these measurements yourself by using my Body Mass Index Calculator and my Waist to Hip Ratio Calculator.

Nutrition and weight issues are central to being healthy and it’s never too late to get started. Use eatTHISdiet as a guide to eating healthier even if you don’t need to lose weight.

August 28, 2006

Last updated: 08/28/06