According to Dr. Giampapa, the goal of a "longevity diet" is to return our bodies to their youthful efficiency, which it can do in three ways.

Boost our youth hormones. The most important hormones for keeping us young are human growth hormone (hGH), which is released by the pituitary gland and converted in the liver to another anti aging hormone called insulin growth factor (IGF 1), and dehydroepiandrosterone (DHEA), which is produced by the adrenal glands.

Starting in our twenties, our bodies slow down production of these hormones by about 10 percent every decade. By age 65, we are making only 15 to 20 percent of the hGH and 10 to 20 percent of the DHEA that we did when we were in our twenties.

With fewer youth hormones around, says Dr. Giampapa, chemical messages don't come and go as efficiently, which reduces the ability of our cells and organs to maintain and repair themselves. We experience loss of muscle and bone density, lowered immunity, and more illnesses, including diabetes and cancer.

Situation hopeless? Not quite, "Increasing the body's production of these hormones can slow the aging process significantly," says Dr. Giampapa. 'And it can be done primarily through diet."

Stem free radical damage.

Our cells use oxygen to produce energy. In the process, they generate free radicals unstable oxygen molecules that damage cells and DNA. Free radicals are also produced by pollution, by the pesticides in our food supply, and by a diet high in chemical additives, refined starches and sugars, artery clogging saturated fat found in meat, whole milk dairy products, tropical oils, and foods like cookies and crackers that contain hydrogenated or partially hydrogenated oils.

Our bodies are good at fending off free radicals when we're young. But as we grow older, we start to lose some of that fight as the damage caused by years of exposure starts to take its toll. We begin to need help from antioxidant nutrients such as vitamins C and E, the minerals zinc and selenium, and the plant chemicals (phytochemicals) in many fruits and vegetables, which join forces with our bodies' internal defense systems.

Replenish our "cellular soup."

Each of our cells contains a substance called cytoplasm, which is made up of fluid, nutrients, and other materials that help make energy and fight freeradical damage, says Israel Kogan, M.D., director of the Anti Aging Medical Center in Washington, D.C

The typical American diet is loaded with chemical additives, pesticides and fertilizers, and other toxic substances, all of which encourage the formation of free radicals, says Dr. Kogan. When our diets are free of these toxins, we protect our cells from free radical damage, give our cytoplasm the nutrients it needs, and help our cells to function at their peak.

A "clean" diet also helps return our bodies to the right level of acidity (pH), which is tremendously important in building up our cellular soup, says Dr. Giampapa. That's because our bodies make hormones, repair cells ' and generally work most effectively at a neutral pH.