September 26, 2007
Eating less and exercising linked to longevity…go figure.
It has been know for about 70 years that caloric restriction prolongs life. In everything from yeast to primates, a significant decrease in calories can extend lifespan by as much as one-third. However, the mechanism of how this happens has remained unclear.
Now, reporting in the September 21 issue of the journal Cell, researchers from Harvard Medical School, in collaboration with scientists from Cornell Medical School and the National Institutes of Health, have discovered two genes in mammalian cells that act as gatekeepers for cellular longevity. When cells experience certain kinds of stress, such as caloric restriction, these genes rev up and help protect cells from diseases of aging.
The new genes are called SIRT3 and SIRT4. They are members of a larger class of genes called sirtuins. (Another gene belonging to this family, SIRT1, was shown last year to also have a powerful impact on longevity when stimulated by the red-wine molecule resveratrol.)
In this paper, the newly discovered role of SIRT3 and SIRT4 drives home something scientists have suspected for a long time: mitochondria are vital for sustaining the health and longevity of a cell.
Mitochondria, a kind of cellular organ that lives in the cytoplasm, are often considered to be the cell's battery packs. When mitochondria stability starts to wane, energy is drained out of the cell, and its days are numbered. SIRT3 and SIRT4 play a vital role in a longevity network that maintains the vitality of mitochondria and keeps cells healthy when they would otherwise die.
When cells undergo caloric restriction, signals sent in through the membrane activate a gene called NAMPT. As levels of NAMPT ramp up, a small molecule called NAD begins to amass in the mitochondria. This, in turn, causes the activity of enzymes created by the SIRT3 and SIRT4 genes--enzymes that live in the mitochondria--to increase as well. As a result, the mitochondria grow stronger, energy-output increases, and the cell's aging process slows down significantly. (Interestingly, this same process is also activated by exercise.)
In fact, the mitochondria appear to be so essential to the cell's life that when all other energy sources inside the cell--including the nucleus--are wiped out, yet the mitochondria are kept intact and functional, the cell remains alive.
Posted by Lisa at September 26, 2007 7:22 AM
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I'm a Canadian dietetics student and love reading your blog. I was wondering, with regards to this article (which I haven't read yet), what is meant by calorie restriction? Is it the commonly accepted 2000 kcal a day? (as in, not overeating?) or something more severe in the 1200 kcal range?
Posted by: Jessica at September 27, 2007 2:30 PM
Caloric restriction varies from person to person. It's estimated to be about 20-25% less calories than your body needs to maintain your current weight. So if a person needs 2000 calories to maintain their weight - they would eat 1500-1600 calories to be on a restricted diet. Keep in mind these diets are also well rounded in whole grains, fruits and vegetables to be sure that all their nutrient needs are met.
Posted by: Lisa at September 27, 2007 3:13 PM