BMI: A number that may not add up

Apr 19 2014, 19:12 IST
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In July 1998, the National Institutes of Health changed what it means to be overweight, defining it as a body mass index of 25 or greater for adults. Reuters In July 1998, the National Institutes of Health changed what it means to be overweight, defining it as a body mass index of 25 or greater for adults. Reuters
SummaryRecent studies have indicated that many with BMI levels at the low end of normal are less healthy than those now considered overweight.

of how fat a person may be. Another problem: the distribution of excess body fat makes a big difference to health. Those with lots of abdominal fat, which is metabolically active, are prone to developing insulin resistance, elevated blood lipids, high blood pressure, diabetes, premature cardiovascular disease, and an increased risk of erectile dysfunction and Alzheimer’s disease.

But fat carried in the hips, buttocks or thighs is relatively inert; while it may be cosmetically undesirable, it is not linked to chronic disease or early death.

Furthermore, a person’s age, gender and ethnicity influence the relationship between BMI, body fat and health risk. Among children, a high BMI is a good indicator of excess fat and a propensity to remain overly fat into adulthood. But for an elderly person or someone with a chronic disease, a BMI in the range of overweight or obesity may even be protective. Sometimes — after a heart attack or major surgery, for example — extra body fat can provide energy that helps the patient to survive. An added layer of fat can also protect against traumatic injuries in an accident.

On average, women have a higher percentage of body fat in relation to total weight than do men, but this does not necessarily raise their health risks. And African-Americans, who tend have heavier bones and weigh more than Caucasians, face a lower risk to health even with a BMI in the overweight range.

While experts continue to debate whether a person can be “fit and fat,” Keri Gans, a dietitian in New York and former spokeswoman for the Academy of Nutrition and Dietetics, points out that physical activity and a healthy diet tend to offset the risks of being overweight.

People with a low-normal or below-normal BMI (less than 18.5) face different health risks. They may lack sufficient reserves to survive a serious health problem, and they are prone to osteoporosis, infertility and serious infections resulting from a weakened immune system.

- Jane E Brody

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