Scientists want to trigger the effects of caloric restriction without the hassle of restricting calories.

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SIRT1: The Human Anti-aging Gene

"No pain, no gain" is the mantra of most diet and exercise programs. However, since a severely restricted diet isn't a good long-term solution for most people, scientists have been trying to find a way to create those same results without actually cutting the calories. What could trigger the body into thinking that it's consuming fewer calories?

Dr. Leonard P. Guarente, a biology professor at M.I.T., hit upon a potential answer when he was studying yeast cells in the mid 1990s. As expected, the cells lived longer when they were given very small amounts of food, and Dr. Guarente began manipulating the cells' genes to determine what part they played in the extended life span. When yeast cells undergoing caloric restriction were endowed with one certain gene, they lived even longer, and when that gene was eliminated by Dr. Guarente, the caloric restriction was for naught, and the yeast cells died. That gene was silent information regulator No. 2, or SIR2.

SIR2 appeared to stop the aging process by stopping the production of waste material in the cell, which allowed the cell to work better for longer. Dr. Guarente was able to duplicate his results with another small organism, the roundworm, which demonstrated that this gene played a role in extending longevity during periods of caloric restriction in several different species. But what of humans?

It turns out humans don't have SIR2, but we have a gene that appears to do the same thing: SIRT1. Both SIR2 and SIRT1 seem to work the same way in the body; they're charged with repairing DNA within the body and suppressing certain genes. Gene silencing, as this suppression is called, is important because if the wrong genes become activated, then the cell's function could be destroyed. It may be that cases of Alzheimer's and diabetes occur because of this type of genetic malfunction.

Dr. Guarente believes that as we age, it's harder for SIR2 and SIRT1 (collectively known as sirtuins) to multitask, so that this gene silencing falls by the wayside. As a result, we end up with the conditions we associate with old age, like cancer, heart disease and the aforementioned Alzheimer's and diabetes. It seems that caloric restriction is so effective because it helps sirtuins work better within the body.

Still, if a calorie restricted diet is unrealistic, then how does knowing this help us live longer?