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­If you've never passed up a buffet with a flashing "all you can eat" sign above it, and if the most strenuous activity you engage in is pointing at your television and clicking the remote, then you may want to pay attention. You smokers can stick around. In fact, there's some hope for you. How? It appears that the key to living a longer life isn't found in swearing off booze, cigarettes, drugs and other pleasures of the flesh. (Avoiding gunshot wounds to vital organs and head-on collisions with 18-wheelers remain good rules of thumb.)

­Instead of leading a healthful life, it appears that the key to longevity is maintaining a near-starvation diet. HowStuffWorks.com in no way encourages you to practice a near-starvation diet. We can say, however, that science has believed in the benefits of caloric restriction for some time now.

When biologists research the process of aging, they keep encountering a pesky question that simply won't die, or at least takes its sweet time doing so: How do such hard-living folks seem to live such long lives? Is diet, genetics, or luck at work here? Let's find out, starting on the next page.