The BMI has been villified almost since the day it appeared on the scene as being a terribly inaccurate measure at worst and a reasonable guess at best. It is famous for overclassifying people with higher than average amounts of muscle, like weight lifters, as “overweight” and underclassifying people with less than average muscle mass, such as the elderly, as being “healthy.” And yet everyone from President Bush to personal trainers still use it. The argument is that for average people, the BMI is pretty accurate. But is that true?
Researchers took 63 volunteers (23 men & 40 women) and then measured their BMI (weight compared to height), body fat percentage, evidence of metabolic syndrome, waist circumference, and body fat mass index (like the BMI but comparing your body fat to your height). They then compared the BMI to the other measures to see if it was a relatively accurate gauge of health.
Surprising no one, the BMI performed miserably. But the interesting part of this research
is just how miserably. The basic gist is that the BMI significantly missed people on both ends of the spectrum (those who are underweight or overweight) that would be referred for treatment based on the other criteria.
Based on the BMI, only 11% of the participants would be strongly encouraged by a doctor to lose weight. Based on waist circumference 25% would. Body fat percentage indicated 28% would. And evidence of metabolic syndrome would indicate 34% needed to lose weight.
63 is a ridiculously small sample size (unless you’re in Hollywood and then it’s an oxymoron). However, I found this study
that tested 14,924 people in a similar manner and came to the same conclusions.
If Not BMI, Then What?
I think it is safe to say that if you are truly interested in measuring your health, the BMI is not a good shortcut. You would do better to factor in your waist circumference, blood pressure, resting heart rate, cholesterol & body fat percentage. But if you need just one number (checking all those factors every week or month is silly), experts are saying
that waist circumference
is the best indicator of health & best predictor of heart disease and diabetes. (Notice that I did not say anything about your thighs – according to scientists, fat stored in your hips and thighs, while irritating to most of us, does not adversely affect your health and in fact, helps women have smarter, healthier babies
. Yet another reason looking like a catwalk model is a bad idea.)
It also happens to be a lot easier to calculate than BMI, for those of us who are math-challenged. Just take a measuring tape, wrap it around your waist (the smallest part of your torso – approx. where your bellybutton is) and measure! If you are a woman, you want to be under 34.5 inches. For a man: under 40 inches. Ideal waist size
for a woman is 32.5 for women and 35 for men.