Is BMI Really the Best Predictor of Health?

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Dr. Alok Gupta, MD
Dr. Alok Gupta, MD

By Alok Gupta

INDIA New England Columnist

Body Mass Index or BMI, a calculation using height and weight, is commonly used to classify patients into weight categories including underweight, normal weight, overweight, and stages of obesity. Medical offices, health and life insurance agencies, and others use this calculation to determine metabolic health and risk for development of disease associated with excess body fat including diabetes and heart disease.

While BMI is the most common measure of body fat, it is argued that it is not the most accurate measure of body fat or risk for disease. One major problem is that BMI does not take into account a person’s athletic ability, muscle mass or fat distribution. Common knowledge provides that muscle weighs more than fat making many fit athletes appear to be overweight or even obese, and neglecting to identify the “unhealthy thin.”

BMI also does not consider fat distribution, even though excess abdominal fat is highly predictive of metabolic and cardiovascular disease namely abdominal fat. These inaccuracies are of special concern at the moment due to recently proposed changes in the Equal Employment Commission that would allow employers to penalize employees failing to meet certain health criteria, including BMI.

There are actually quite a few alternatives ways to determine fat mass and risk for disease. Waist circumference, waist to height ratio and waist to hip ratio, may be the least time consuming and cost effective of the various measures. All three are based on the theory that abdominal fat, is more problematic for health. Waist circumference, by far the simplest, defines abdominal obesity as circumference >80 cm (31.5 inches) for women and >90 cm (35.5 inches) for men. Waist to height ratio, just like it sounds compares the waist circumference to the height. A value >0.5 indicates abdominal obesity. Waist to hip ratio is similar to the waist to height ratio is considered to have about the same value in identifying those at risk for disease.

The World Health Organization defines abdominal obesity as a waist to hip ratio >0.85 in women and >0.9 in men. One of the draw backs of these methods include subjecting patients to the measurement of the waist and hip unclothed. Many patients are reluctant to step on the scale, let alone present their bare waist and/or hip for measurement. Another disadvantage is that this measurement does not differentiate subcutaneous fat (stored just under the skin), from that within the abdominal cavity which is consider the greater culprit for disease. When one of these measures is combined with the BMI, patients with high BMI and low measurements would be more appropriately classified as non-obese and possibly identify patients with normal BMI but with elevated risk for disease based on abnormal abdominal obesity.

Other more costly, time consuming and sometimes invasive measures of body fat measurement include 3-point caliper testing, bio impedance, and hydrostatic. While these tests are arguably the better measure of fat they are impractical for most primary care practices due to the special equipment and training, time required for testing, or cost.

Why with all these other options do we still use BMI? Well, it is easy and cheap, but that is probably not a good reason to continue to use this as the standard. More specialized testing like 3-point caliper testing, and bio impedance have started to find their way into obesity treatment practices and some other specialties. While I see many patients balking at the thought of having their waist measured at each appointment, a yearly assessment as part of yearly screen at an annual wellness visit or physical could be cost effective as well as be a better predictor of health problems due to weight.

(Dr. Alok K. Gupta is an Internist, a doctor for adults. He is a Board Certified in Internal Medicine. He completed his residency in Internal Medicine at Salem Hospital in Salem, Massachusetts. Part of the training was also at Massachusetts General Hospital. Dr. Gupta has been practicing Internal Medicine since 1998. He was in upstate New York for six years. Recently, he had been practicing in Manassas, and now is in practice in Gainesville. Visit him on the web at www.alokguptamd.com )

 

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