Severe Diet Doesn’t Prolong Life, at Least in Monkeys

Posted by: on Sep 14, 2012 | No Comments

The results of a long-awaited study of calorie restricted diets in rhesus monkeys which began in 1987, are finally in. But it did not bring the vindication calorie restriction enthusiasts had anticipated. It turns out the skinny monkeys did not live any longer than those kept at more normal weights. Some lab test results improved, but only in monkeys put on the diet when they were old. The causes of death — cancer, heart disease — were the same in both the underfed and the normally fed monkeys.

Lab test results showed lower levels of cholesterol and blood sugar in the male monkeys that started eating 30 percent fewer calories in old age, but not in the females. Males and females that were put on the diet when they were old had lower levels of triglycerides, which are linked to heart disease risk. Monkeys put on the diet when they were young or middle-aged did not get the same benefits, though they had less cancer. But the bottom line was that the monkeys that ate less did not live any longer than those that ate normally.

Rafael de Cabo, lead author of the diet study, published online on Wednesday in the journal Nature, said he was surprised and disappointed that the underfed monkeys did not live longer. Like many other researchers on aging, he had expected an outcome similar to that of a 2009 study from the University of Wisconsin that concluded that caloric restriction did extend monkeys’ life spans.

The idea that a low-calorie diet would extend life originated in the 1930s with a study of laboratory rats. But it was not until the 1980s that the theory took off. Scientists reported that in species as diverse as yeast, flies, worms and mice, eating less meant living longer. And, in mice at least, a low-calorie diet also meant less cancer. It was not known whether the same thing would hold true in humans, and no one expected such a study would ever be done. It would take decades to get an answer, to say nothing of the expense and difficulty of getting people to be randomly assigned to starve themselves or not.

Now, with the new study, researchers are asking why the University of Wisconsin study found an effect on life span and the National Institute on Aging study did not. There were several differences between the studies that some have pointed to as possible explanations. The composition of the food given to the monkeys in the Wisconsin study was different from that in the aging institute’s study. The University of Wisconsin’s control monkeys were allowed to eat as much as they wanted and were fatter than those in the aging institute’s study, which were fed in amounts that were considered enough to maintain a healthy weight but were not unlimited.The animals in the Wisconsin study were from India. Those in the aging institute’s study were from India and China, and so were more genetically diverse.

Dr. de Cabo, who says he is overweight, advised people that if they want to try a reduced-calorie diet, they should consult a doctor first. If they can handle such a diet, he said, he believes they would be healthier, but, he said, he does not know if they would live longer.

Then there is Mark Mattson, chief of the laboratory of neurosciences at the National Institute on Aging, who was not part of the monkey study. He believes there is merit to caloric restriction. It can help the brain, he said, as well as make people healthier and probably make them live longer. Dr. Mattson, who is 5-foot-9 and weighs 130 pounds, skips breakfast and lunch on weekdays and skips breakfast on weekends. “I get a little hungry,” he acknowledged. “But we think being hungry is actually good.”