I’ve been pointing out, for quite some time, that science is telling us body weight is a poor indicator of overall health. And, here’s another study, from the University of Florida, that concludes body weight is a poor predictor of Type 2 diabetes risk. But, before I get to the study, let’s examine how measuring weight on a scale came to be the end-all, be-all of determining health.
The Body Mass Index (BMI) was developed in the 1800s. It’s based on the belief that weight is associated with height. And, to an extent, that is true. A tall person has more mass than a short person and, therefore, the tall individual should weigh more than a shorter individual. A formula was developed to use the correlation of height to weight to determine if someone was underweight, normal/healthy weight, or overweight for his height.
Over time, the formula and standards for BMI have been tweaked to reflect other physiological realities, such as men tend to weigh more than women of the same height due to their greater lean mass and there’s a difference in expected weight when one is growing (children and adolescents) as well as when one is in decline (elderly).
Physicians worldwide began using BMI as a data point in determining an adult’s overall health in the 1980s and the obese category was added. The current BMI formula (lbs/inches² X 703) and associated chart (below) was approved in 1998 and is used by doctors to this day. This is why we’re asked our height and told to step on a scale when we visit the doctor.
The Trouble with BMI
But, common sense tells us BMI can’t possibly determine health for many individuals. Think of elite athletes – epitomes of fitness and health. Most athletes, male and female, have more muscle mass than their non-athlete counterparts. Because muscle weighs more than fat, some athletes fall into the overweight or obese categories on the BMI. Conversely, genetically thin people who are sedentary smokers can fall into the healthy weight category on the BMI and yet are at high risk for hypertension, heart disease and stroke due to their high-risk lifestyles.
As such, doctors are cautioned to use BMI as only one data point of many when determining the health of patients. Though, how much or little importance a doctor gives BMI tends to be subjective and varies from one doctor to another.
Recently, science has called into question whether or not BMI should be used to determine the health of any individual. Namely, a growing list of studies has shown individuals who live active lifestyles but fall into the overweight and obese categories on the BMI are healthier, in terms of disease risk, quality of life and morbidity, compared to individuals in the normal range on the BMI but who live sedentary lifestyles. And, as a group, those in the underweight category have the greatest risk for disease, poor quality of life and morbidity compared to the other groups as a whole.
The University of Florida’s study I cited above can be added to the list. The study measured BMI and body fat percentages in 6,335 adults over 40 who have never been diagnosed with diabetes. The results showed that high body fat percentage was a better predictor that an individual would have an abnormally high blood glucose level (an indicator of Type 2 diabetes) than falling above the healthy category on the BMI.
The beauty of the BMI, and the likely reason it just won’t go away, is how simple it is to use: measure height, step on a scale, consult a chart. Body fat percentage is more difficult to determine. Laboratories, usually using water tanks or sophisticated machines, are the only way to learn a person’s exact body percentage. That, obviously, is too inconvenient and costly for the average person. The use of calipers (below) is a decent estimator of body fat percentage. But their accuracy is highly dependent upon the experience and skill of the person using the calipers.
So far, the easiest, cheapest and most reliable way to determine whether a person has a body fat percentage in the healthy range (under 30% for adult women, under 25% for adult men) is the waist-to-hip ratio. Anyone who can get her hands on a tape measure and a calculator can determine her ratio: