Overweight people with chronic diseases often live longer than their normal-weight counterparts. Overweight people with chronic diseases often live longer than their normal-weight counterparts.
A few years ago, Mercedes Carnethon, a diabetes researcher at the Feinberg School of Medicine at Northwestern University in Illinois, found herself pondering a conundrum. Obesity is the primary risk factor for type 2 diabetes, yet large numbers of normal-weight people also develop the disease. Why?
In research carried out to answer that question, Carnethon found something even more puzzling: diabetes patients of normal weight are twice as likely to die prematurely 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....
Experts are searching for explanations. One idea is that once a chronic disease develops, the body becomes catabolic, meaning it needs higher energy and caloric reserves than usual.
If patients do not have those reserves, they may become malnourished even though their weight is normal, says Dr Gregg Fonarow, one of the directors of the preventive cardiology program at the University of California, Los Angeles.
Some researchers suspect genetics. Maybe thin people who develop diabetes and other chronic ailments have gene variants that make them more susceptible to these illnesses and put them at greater risk once they become ill. Heart disease in thin people may represent a different illness from heart disease in heavier people, Lavie says.
It might be that doctors do not treat thin patients as aggressively as they do heavier patients – or that the yardstick itself is to blame. Most researchers assess obesity by measuring body mass index, a simple ratio of height and weight.
But BMI does not take into account body fat, lean muscle mass, metabolic abnormalities and other nuances of physical composition.