Since the beginning of time, man has sought fruitlessly for the Fountain of Youth. Today legions of scientists of all persuasions believe that it is various concoctions of vitamins, minerals, hormones and other molecules that can retard the aging process. Almost all are bogus, and even approaches to make our skin look younger are purely cosmetic.

And yet an array of studies done in tissue cultures, yeast, bacteria, tiny worms called nematodes, fruit flies and various mammals have shown that it is possible to promote longevity. Far and away the most effective method is restricting caloric intake by as much as 30 percent. In every case, as long as optimum nutritional requirements are met, average and maximum life expectancies are increased by an equal amount.

And now, in a paper just published in the prestigious journal Science, we've learned that restricting food intake dramatically prolongs life in a close relative of man: the monkey. Conducted over 20 years, the study has found that only 20 percent of the calorically restricted animals have died, compared with 50 percent of those allowed to eat anything they want.

The restricted animals look much younger, have fewer physical disabilities and have a much lower prevalence of diabetes, heart disease and cancer. Their immune function is much better, and every marker that measures biologic age is improved. Interestingly, caloric restriction does not lead to significant differences in weight, as these animals handle calories much more efficiently.

The fact that restricting calories prolongs life expectancy in monkeys makes it highly likely that a similar effect occurs in humans. However, these monkeys live in cages, in an ideal environment, and are not exposed to the myriad stressors and environmental influences that characterize our lives. And let's face it; how many of us have the willpower to essentially starve ourselves for our entire lives? It is this fact that has led scientists to attempt to identify the mechanism whereby restricting food intake prolongs life expectancy. If only we could find the "magic bullet" that would allow us to mimic caloric restriction while consuming a more liberal diet.

To date, the exact mechanism whereby caloric restriction exerts an effect remains elusive. Studies already have been conducted to determine whether antioxidants, hormone replacement and genetic manipulation are beneficial. Sadly, the evidence in man suggests the exact opposite. Too much of the antioxidants vitamins C, E and A has the exact opposite effect, increasing the risk of cancer, heart disease and Alzheimer's disease and, if anything, shortening life expectancy. And DHEA, a precursor of steroids and sex hormones, prolongs immune function and life expectancy in mice but seems to be of no value in man. Even manipulating the genetic composition of mice does not appear to be of any benefit.

Currently, attention is being focused on flavonoids in red wine. Studies have shown that in moderation (two glasses daily), red wine reduces risks of heart attacks and cancer and may prolong life. Some have suggested that resveratrol, an antioxidant flavonoid, may be the elixir of youth in the wine. Though it already is hawked as a way to prolong life, a great deal of work needs to be done before resveratrol will be proved to be of any value. There are those who believe that the health advantages of red wine come from the calming effects of small amounts of alcohol.

And now comes a study, published in the journal Nature, showing that rapamycin prolonged life in mice by 20 percent. Rapamycin was first isolated from bacteria found in the soil of Easter Island, in Polynesia. It already is used widely to prevent organ rejection following transplantation. The molecule suppresses a biochemical pathway called mTOR that accelerates cellular metabolism and proliferation. This enzyme pathway is slowed in caloric restriction, leading scientists to study its effect on the aging process. But don't try this drug; the side effects are huge.

These studies all hold promise that someday a strategy will be developed to substantially prolong life expectancy in man. Some believe that 200 years is possible. But remember that it's not how long we live, but how well. Sadly, beyond 105, most survivors reside in nursing homes and are significantly dependent. It is the rare 80-year-old who wants his life prolonged. People want assurance that their lives will be disease-free and filled with dignity and that they won't need to depend on anyone.

Dr. David Lipschitz is the author of the book "Breaking the Rules of Aging." To find out more about Dr. David Lipschitz and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com. More information is available at www.DrDavidHealth.com.