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Stay Hungry, Live Longer: the Science Behind the Calorie Restriction Diet

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With obesity come related diseases such as diabetes, heart disease, kidney disease and cancer. By 2040, according to several studies, it's projected that two-thirds of all American adults will be obese or overweight. Childhood obesity is already at crisis levels, with dramatic increases in type 2 diabetes among the very young. As those overweight kids transition to overweight adults, mortality levels will spike as they fall victim to early heart attacks, strokes, kidney failure and other obesity-related ailments. Meanwhile, baby boomers who've gained a pound or two a year in every year of middle age will be lurching heavily and unhealthily into their late 60s and 70s.

"Definitely as you age, you need fewer calories," says Jo Ann Carson, Ph.D., who teaches clinical nutrition at University of Texas Southwestern Medical School and is a spokesperson for the American Dietetic Association. "Your metabolism slows down, requiring fewer calories to function. But those calories should come from better quality nutrients."

Carson offers a simple formula for calculating how much to decrease daily food consumption to reap the health benefits. For women, subtract 7 calories per day (from an average of 2,000) for every year past age 19. For men, it's 10 calories per day. Between ages 20 and 50, that's a gradual decrease of between 210 and 300 calories (the equivalent of a couple of slices of buttered toast).

Guidelines issued by the U.S. Department of Agriculture in 2005 (the next set of guidelines will be issued next year) also advise that Americans need to eat fewer calories, fats and carbs, and should add more fruits, vegetables and whole grains to their diets. Also recommended are 60 minutes of moderate-to-vigorous physical activity most days of the week.

Carson points to studies that show that calorie restriction followers have healthier glucose and insulin levels as they age, less incidence of inflammatory diseases and do better on cognitive function tests.

"There's something to this idea that getting just the right amount of calories for survival is an important way to manage health," she says. "They find that place where they eat just enough, somewhere between 1,300 and 1,500 calories a day. The body is remarkable in how it adjusts and tries to maintain a steady state to keep you alive and functioning."

The few calorie restriction studies using human subjects involved people voluntarily on the diet already, including one project at the Washington University School of Medicine looking at heart health among several groups, including 28 members of the Calorie Restriction Society who had been eating a CR diet for six years. The CR followers' hearts were more elastic and able to relax better between beats compared to subjects who ate a standard Western diet and did endurance exercise training. That study concluded that leanness helped prevent disease, but only calorie reduction slowed down aging.

The most recent short-term study on CR, conducted at the University of Munster in Germany and published online in January by the National Academy of Sciences, lasted three months and determined that reducing calorie intake by 30 percent improved memory ability by 20 percent in elderly individuals (average age 60.5 years).

Evidence keeps mounting showing the many positive effects of eating less. But is a lifetime of meager meals a guarantee of long life?

The skunk at the calorie restrictors' picnic is longevity expert Steven Austad, Ph.D., author of the book Why We Age and professor of biology at University of Texas Health Science Center at San Antonio. He doesn't believe that either CR or resveratrol will have as much of a "youthening" effect on humans as they do on lab animals. As he's told several conventions of the Calorie Restriction Society in the past, what works on flies and mice fails seven out of 10 times on people.

"We know that CR extends life in some animals, in some it doesn't," Austad says. "Some kinds of mice it works, some it doesn't. Some fruit flies it does, some it doesn't. People who study this tend to forget the experiments in which it didn't work."

Austad says he warns extreme calorie restrictors that "the jury is still out" on whether eating so little will add healthy years. "It might suppress the immune system and you could die from the next flu epidemic," he says. Or you could end up at 80 with muscles too weak to support even a thin body. "It would be extremely interesting and exciting if reducing your food intake would extend your life. But people in the aging community tend to jump on the bandwagon and make the leap from fruit flies to humans a little too enthusiastically."

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Elaine Liner
Contact: Elaine Liner