Suppose you could live a longer, healthier life if you were willing to eat about half what you normally do and spend every day feeling cold and hungry? Sound impractical? Still, a caloric restriction diet is the only diet regime so far that has been proven to actually extend the lives of laboratory animals.

Caloric restriction limits an animal's intake to about one-half to two-thirds of what it normally requires. The key to this diet is being undernourished without being malnourished. From spiders to rodents to primates, animals on this diet have been shown to live longer, have lower cholesterol, and be less susceptible to diseases such as Parkinson and Alzheimer's.

The problem is that this diet is a tough one to stick to. Scientists are hard at work trying to figure out the underlying mechanisms. Right now, the leading theory is that caloric restriction diets force our bodies to process fuel more efficiently and consequently reduce the damage caused by what is known as the oxygen paradox.

On the one hand, we need oxygen to produce fuel. But on the other, this process results in a special form of the oxygen molecule that ultimately oxidizes and damages our body's tissues. A caloric-restriction diet not only reduces the harmful byproducts of metabolism, but may even produce extra enzymes that neutralize these byproducts.

Even so, there are many different interpretations of exactly what happens on caloric restriction diets, and whether they're a viable option for humans. So until the jury reaches a verdict, eating healthy and in moderation is still the best strategy for a long and healthy life.