More Data Suggests Fitness Matters More Than Weight - NYTimes.com
A few years ago, Mercedes Carnethon, a diabetes researcher at the Feinberg School of Medicine at Northwestern University, found herself pondering a conundrum. Obesity is the primary risk factor for Type 2 diabetes, yet sizable numbers of normal-weight people also develop the disease. Why?
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In research conducted to answer that question, Dr. Carnethon discovered something even more puzzling: Diabetes patients of normal weight are twice as likely to die as those who are overweight or obese. That finding makes diabetes the latest example of a medical phenomenon that mystifies scientists. They call it the obesity paradox.
In study after study, overweight and moderately obese patients with certain chronic diseases often live longer and fare better than normal-weight patients with the same ailments. The accumulation of evidence is inspiring some experts to re-examine long-held assumptions about the association between body fat and disease.
Dr. Carl Lavie, medical director of cardiac rehabilitation and prevention at the John Ochsner Heart and Vascular Institute in New Orleans, was one of the first researchers to document the obesity paradox, among patients with heart failure in 2002. He spent more than a year trying to get a journal to publish his findings.
Research that does tease apart weight and fitness — like a series of studies conducted by Steven Blair at the Cooper Institute in Dallas — shows that being fat and fit is better, healthwise, than being thin and unfit. Regular aerobic exercise may not lead to weight loss, but it does reduce fat in the liver, where it may do the most metabolic damage, according to a recent study at the University of Sydney.
“More often than not, cardiovascular fitness is a far more important predictor of mortality risk than just knowing what you weigh,” said Glenn Gaesser, author of “Big Fat Lies” and director of the Healthy Lifestyles Research Center at Arizona State University.
In 2005, an epidemiologist, Katherine Flegal, analyzed data from the National Health and Nutrition Examination Survey and found that the biggest risks of death were associated with being at either end of the spectrum — underweight or severely obese. The lowest mortality risks were among those in the overweight category (B.M.I.s of 25 to 30), while moderate obesity (30 to 35) offered no more risk than being in the normal-weight category.
Whatever the explanation for the obesity paradox turns out to be, most experts agree that the data cast an uncertain light on the role of body fat. “Maintaining fitness is good and maintaining low weight is good,” Dr. Lavie said. “But if you had to go off one, it looks like it’s more important to maintain your fitness than your leanness. Fitness looks a little bit more protective.”