Being overweight is unhealthy. The medical community never tires of predicting an early demise for obese people, and strongly urging them to lose weight. But in fact, the latest science says that fat people live longer and can tolerate higher levels of stress.

"The classic view is that obesity is an illness that has to be cured," says Professor Achim Peters of the University of Lübeck in Germany. "But it’s not an illness. In fact, it’s even a good thing."

The obesity specialist has been fighting this stigmatizing view of obesity for years. His own body mass index (B.M.I.) of 23 puts him in the normal weight category, so the issue does not personally concern him. Along with neuroscience professor Bruce McEwen of Rockefeller University in New York, he has developed a theory known as the "obesity paradox" (Physiology and Behavior, Vol. 106, p. 1, 2012), according to which obesity is a healthy way of managing stress.

The foundation of the theory is Peters' notion of the “selfish brain” in which the brain will claim the energy it needs from the body, even if that puts the body at risk. In cases of extreme hunger, inner organs, for example, lose up to 40% of their weight, but the brain loses only 1%.

When people are not stressed, their brains use 50% of their body’s glucose, and this rises to 90% under stressful conditions. With obese people, however, according to the theory, the brain is short-changed because the body is building fatty deposits instead. Because it is not getting the glucose it wants, the brain must increase its energy demands. The fat person eats more to cover the selfish brain’s needs, but again only a small portion of these calories go to the brain, and the rest goes into building fat deposits.

Hence, according to this theory, obese people cannot help being obese. It is their body’s reaction to chronic stress.

Big bottom protection

The longevity of overweight people first came to researchers’ attention in 1999 when Edmund Lowrie at the University of California in San Francisco noticed that his thinner dialysis patients died before the overweight ones. It then came to light that even obese people who have suffered heart attacks live longer, with the same holding true after major operations, sepsis, strokes, brain hemorrhage, even in patients suffering from rheumatism and cancer. The obese patients always came out ahead, even if their B.M.I. was as high as 30, which would mean that a person 1.70 meters (5.6 feet) tall weighs 85 kilos (187 lbs).

The important distinction was whether the corpulent person was carrying the extra weight around the waist. That type of fatness, which surrounds the inner organs, is indeed life-threatening as soon as a man’s waist reaches 102 centimeters (40 inches) and a woman’s 88 centimeters (34.6 inches). But heavy arms and legs, hips and bottom act more as a form of protection than a threat.

In 2010, an experiment involving 27,000 Danes with higher B.M.I.s bore this out, as did a 15-year-long experiment, conducted by Australian and Scandinavian scientists, with 8,000 inhabitants of Mauritius (International Journal of Epidemiology, Vol. 41, p. 484, 2012).

"Being overweight is not as dangerous as was previously thought," says health researcher Ingrid Mühlhauser of the University of Hamburg. Her study of Germans with a B.M.I. of around 27 shows they have a longer life expectancy than people with a B.M.I. of 20 (58 kilos or 128 lbs at 1.70 meters or 5.6 feet). Overweight people do have a greater tendency to heart problems or diabetes but not stroke, says Mühlhauser. And B.M.I.s over 35 continue to be highly dangerous. "The highest life expectancy is when there’s a B.M.I. of 27," she says.

Being thin is a predisposition

According to Peters, the only way to lose weight is to lower stress levels. Part of that stress is caused by the negative view society has of obese people. According to Dr. Thomas Ellrott of the University of Göttingen’s Institute of Nutrition Psychology, 14% of Germans said that if they were employers they would not hire overweight people. "Stigmatization not only doesn’t help fat people, it makes the problem worse."

Says Peters, "The answers you are usually given for the causes of obesity are lack of willpower, immoderation, greed, laziness.” Yet recent data have shown that overweight people exercise a great deal more cognitive control over their eating behavior than other people do.

Being thin is a predisposition, not an achievement, and for thin people gaining weight is as difficult as it is for fat ones to lose it. People with sleep disturbances or money troubles, or who are under constant pressure, should not add to their problems by worrying about a few extra pounds, berating themselves for their lack of self-discipline, Peters says. It might help to remember that thin, overly stressed people are far worse off. "I always ask myself: am I thin and relaxed, or thin and under pressure,” Peters says. "If the latter, I’m in the worst category."