Living a longer life: whose advice helps?

Among the earliest and most ardent proponents of calorie restriction as a means to extending life, Roy Walford, a UCLA physician, began exploring the links between food and longevity in the 1960s. He restricted the caloric intake of mice by 40% and found that they lived almost twice as long as other mice, an experiment that has often been repeated in other labs by other researchers -- on mice as well as other organisms.

Walford then put himself on a low-calorie, nutrient-dense diet -- around 1,600 calories a day -- and adhered to it rigorously. He wrote several books about diet and longevity, including "Beyond the 120-Year Diet: How to Double Your Vital Years." He remained active in the Calorie Restriction Society, a group that promotes this approach to longevity. He died of Lou Gehrig's disease at age 79.

The verdict: Researchers in the field of gerontology and longevity commend Walford's research. Though many aren't ready to suggest humans undertake caloric restriction, they recognize it is the only known intervention shown to prolong life in multiple species, including, most recently, primates. It works, scientists believe, because it triggers alterations in metabolic pathways involved in energy utilization. In animal studies, calorie restriction has also resulted in a reduction in age-related disabilities, including cataracts, arthritis, cognitive decline and kidney disease.

While evidence is promising, it's too soon to jump from the Petri dish to the public, Perls says. "No human studies have proven that calorie-reduction works for people. Plus, getting people to comply is unlikely."

Ordovas believes the sacrifices in quality of life that may accompany the diet -- loss of ability to reproduce in some animals, and lower energy -- may not be worth it. The National Institute on Aging continues to fund calorie-restriction studies.

Jim Fixx

1932-84

Jim Fixx's passion for running started after his dad had a heart attack at age 35. His father died of a heart attack eight years later. The experience prompted Fixx, an overweight smoker, to start running to prevent a similar fate. Thus, Fixx jump-started a love of jogging among sedentary Americans. His book "The Complete Book of Running" touted the health benefits of running and claimed that regular running offered virtual immunity to heart disease. He hoped that by helping eliminate the nation's No. 1 killer, he would help extend lives. His 1978 book sold half a million hardback copies in the United States in nine months, and hit No. 1 on the New York Times book list.