Behind the resveratrol test is a considerable degree of scientific theory, some of it well established and some yet to be proved. Dr. Sinclair’s initial interest in resveratrol had nothing to do with red wine. It derived from work by Leonard Guarente of the Massachusetts Institute of Technology, who in 1995 found a gene that controlled the longevity of yeast, a single-celled fungus. Dr. Guarente and Dr. Sinclair, who had come from Australia to work as a post-doctoral student in Dr. Guarente’s lab, discovered the mechanism by which the gene makes yeast cells live longer. The gene is known as sir-2 in yeast, sir standing for silent information regulator, and its equivalent in mice is called SIRT-1.

Dr. Guarente then found that the gene’s protein needs a common metabolite to activate it and he developed the theory that the gene, by sensing the level of metabolic activity, mediates a phenomenon of great interest to researchers in aging, the greater life span caused by caloric restriction.

Researchers have known since 1935 that mice fed a calorically restricted diet — one with all necessary vitamins and nutrients but 40 percent fewer calories — live up to 50 percent longer than mice on ordinary diets.

This low-calorie-provoked increase in longevity occurs in many organisms and seems to be an ancient survival strategy. When food is plentiful, live in the fast lane and breed prolifically. When famine strikes, switch resources to body maintenance and live longer so as to ride out the famine.

Researchers had long supposed that the increase in longevity was a passive phenomenon: during famine or on a low-calorie diet, organisms would have lower metabolism and produce less of the violent chemicals that oxidize tissues. But Dr. Guarente and Dr. Sinclair believed that longer life was attained by an active program that triggered specific protective steps against the diseases common in old age. It was because these diseases were averted in calorie restriction, they believed, that animals lived longer.

Most people find it impossible to keep to a diet with 40 percent fewer calories than usual. So if caloric restriction really does make people as well as mice live longer — which is plausible but not yet proved — it would be desirable to have some drug that activated the SIRT-1 gene’s protein, tricking it into thinking that days of famine lay ahead.

In 2003 Dr. Sinclair, by then in his own lab, devised a way to test a large number of chemicals for their ability to mimic caloric restriction in people by activating SIRT-1. The champion was resveratrol, already well known for its possible health benefits.