How depressing, how utterly unjust, to be the one in your social circle who is aging least gracefully.
In a laboratory at the Wisconsin National Primate Research Center, Matthias is learning about time's caprice the hard way. At 28, getting on for a rhesus monkey, Matthias is losing his hair, lugging a paunch and getting a face full of wrinkles.
Yet in the cage next to his, gleefully hooting at strangers, one of Matthias' lab mates, Rudy, is the picture of monkey vitality, although he is slightly older. Thin and feisty, Rudy stops grooming his smooth coat just long enough to pirouette toward a proffered piece of fruit.
Tempted with the same treat, Matthias rises wearily and extends a frail hand. "You can really see the difference," said Ricki Colman, an associate scientist at the center who cares for the animals.
What a visitor cannot see may be even more interesting. As a result of a simple lifestyle intervention, Rudy and primates like him seem poised to live very long, very vital lives.
This approach, called calorie restriction, involves eating about 30 percent fewer calories than normal while still getting adequate amounts of vitamins, minerals and other nutrients. Aside from direct genetic manipulation, calorie restriction is the only strategy known to extend life consistently in a variety of animal species.
How this drastic diet affects the body has been the subject of intense research. Recently, the effort has begun to bear fruit, producing a steady stream of studies indicating that the rate of aging is plastic, not fixed, and that it can be manipulated.
In the last year, calorie-restricted diets have been shown in various animals to affect molecular pathways likely to be involved in the progression of Alzheimer's disease, diabetes, heart disease, Parkinson's disease and cancer. Earlier this year, researchers studying dietary effects on humans went so far as to claim that calorie restriction may be more effective than exercise at preventing age-related diseases.
Monkeys like Rudy seem to be proving the thesis.
The findings cast doubt on long-held scientific and cultural beliefs regarding the inevitability of the body's decline.
"Calorie restriction has the potential to help us identify anti-aging mechanisms throughout the body," said Richard Weindruch, a gerontologist at the University of Wisconsin who directs research on the monkeys.
Aging is a complicated phenomenon, the intersection of an array of biological processes set in motion by genetics, lifestyle, even evolution itself.
Still, in laboratories around the world, scientists are becoming adept at breeding animal Methuselahs, extraordinarily long lived and healthy worms, fish, mice and flies.
In 1935, Clive McCay, a nutritionist at Cornell University, discovered that mice that were fed 30 percent fewer calories lived about 40 percent longer than their free-grazing laboratory mates. The dieting mice were also more physically active and far less prone to the diseases of advanced age.
McCay's experiment has been successfully duplicated in a variety of species. In almost every instance, the subjects on low-calorie diets have proven to be not just longer lived, but also more resistant to age-related ailments.
"In mice, calorie restriction doesn't just extend life span," said Leonard Guarente, professor of biology at the Massachusetts Institute of Technology. "It mitigates many diseases of aging: cancer, cardiovascular disease, neurodegenerative disease. The gain is just enormous."