Fat Loss May Lead to a Longer Life

Study in mice helps explain the benefits of living lean

If you eat less, a lot less, will you live longer? Maybe.

Researchers have known for quite a while that lean mice that live on severe calorie-restricted diets live longer than their well-fed counterparts, but they did not know the reasons behind that difference. Now, scientists think they may have found the answer.

Researchers from the Massachusetts Institute of Technology (MIT) explained in the journal Nature that calorie restriction activates a gene called Sirt1. And once Sirt1 becomes active, it activates the PPAR-gamma gene that is responsible for fat storage.

"A diet with very low calories seems to slow down aging and mitigate diseases of aging," Dr. Leonard Guarente, a professor of biology at MIT and the lead researcher, told HealthDay . "But what we haven't known is how that works."

Until now, that is.

Guarente and his colleagues discovered that once Sirt1 and PPAR-gamma become active because they sense a scarcity of calories, fat cells stop storing fat and begin releasing fat. In humans, the Sirt1 gene is called SIR2.

"The fat then gets pushed out of the cells into the blood, where it gets metabolized," he said. "This is a process that correlates with good health and longevity."

By understanding how living lean can help the body live longer, researchers have taken the first step in a process that could lead to the development of drugs that could produce the benefits of calorie restriction without having to live on a diet of deprivation.

"I think that we can have drugs that can deliver some of the benefits of a low-calorie diet, without having to live a Spartan existence to get the benefit," Guarente said.

Not everyone agrees, however, that a diet pill will be the answer.

"The two things that work all the time are diet and exercise," Dr. Heidi Tissenbaum, a gene expert at the University of Massachusetts Medical School, told HealthDay . "I don't think that we will ever be able to take a pill and eat whatever we want."

Also, Tissenbaum said, longevity benefits are unclear.

"We don't know when these genes are active in the adult life span," she said. "We know how they act in the cell, but we don't know, until we have the data in mice and humans, that if you change one thing you can extend life span."

Dr. Ronen Marmorstein, a researcher from the Wistar Institute at the University of Pennsylvania , added that it's "pretty clear that Sirt1 activity has an effect on fat metabolism and storage…[but] whether or not there is a longevity connection in mammals is still an open question."