Are BMI guidelines for the birds?
Saturday, June 27, 2009 0:38Q. I recently read that the standard BMI calculation and guidelines aren't accurate for African-Americans and other ethniticies. Can you explain why and do you have recommendations for ethnic specific guidelines?
A. Your BMI, or body mass index, is nothing more than a way of expressing your weight in relation to your height. When we say that a BMI of between 19 and 25 is considered ideal, we're really just saying that for every height, there is a suggested healthy weight range. I'm 5'9" for example. The suggested healthy weight range for me is 128 to 169. (Click here to look up your BMI)
I think you're probably referring to a recent article in the British Journal of Nutrition (reported in the Washington Post), which points out that the BMI guidelines are based on statistics gathered in a predominantly Caucasian population.
Because of differences in average bone density, lean muscle mass, and so on, the BMI guidelines may be misleading for non-Caucasians. For example, it might underestimate healthy weight range for some people of African descent and overestimate the range for some of Asian descent. Even for Caucasians, though, the BMI is a fairly crude gauge of body composition. For example, it's not a good guide for athletes, who have more muscle mass, or for the elderly, who have lost muscle and bone mass.
The BMI guidelines are supposed is to help identify people who may have too much (or too little) body fat. Other ways to gauge whether you are carrying around an unhealthy amount of fat include:
Have a fitness trainer measure your body fat percentage. The recommended percentage depends on your age and gender but as a very general guideline, women should try to keep body fat under 30% and men under 25%. There are several methods of measuring body fat. The most accurate is also the least convenient: It involves being submerged in a tank of water. A fitness trainer can get a pretty good estimate using body fat calipers--but good training and technique are essential. Those scales and hand-held devices that calculate body fat by measuring electrical impedance are notoriously inaccurate.
Measure your waist size. A waist measurement of more than 35" for women or 40" for men increases your risk of heart disease and other diseases.
Calculate your waist-to-height ratio by dividing your waist measurement by your height. If you are 5'5" and your waist measures 32", your ratio would be 32/65 or 0.49. A ratio of less than 0.50 is considered healthy.
Calculate your waist-to-hip ratio by dividing your waist measurement by your hip measurement. If your waist measures 32" and your hips measure 38", your ratio would be 32/38 or 0.84. As a general rule, women are shooting for a ratio of less than 0.8 and guys for a ratio of 0.95 or less.
Ask your physician for individual guidance. Your physician sees the whole you, not just a single measurement or statistic. If you're not sure whether your weight is healthy or not, ask your health care provider for input.