By Maureen Williams, ND

Healthnotes Newswire (May 11, 2006)—The newest findings on dieting suggest that a low-calorie diet might do more than bring about weight loss—it might also slow the aging process.

Millions of people embark on weight-loss diets every year. Although some of these diets rely on changing proportions of fats, carbohydrates, and protein, only those that involve calorie restriction have been proven to lead to healthy and sustainable weight loss. The body responds to calorie restriction by altering metabolism. Over time, taking in fewer calories will result in the body expending less energy.

Laboratory animals eating a low-calorie diet live longer than animals that eat a normal amount of calories. As the low-calorie diet causes energy output to decrease, the body produces fewer free radicals (compounds that cause much of the damage to cells that occurs with aging). This might explain in part the increased longevity seen in the dieting animals, but other adaptive changes are likely to contribute as well.

The Journal of the American Medical Association published the new study on calorie restriction in humans. Forty-eight overweight adults were randomly divided into four groups, each assigned to a diet for six months: a normal weight-maintenance diet; a diet with 25% fewer calories than needed to maintain weight; a diet with 12.5% fewer calories than needed to maintain weight, plus a 12.5% increase in energy output through exercise; and a very-low-calorie diet providing 890 calories per day (a typical adult eats about 2,000 calories per day). The study was designed so that if dieters lost 15% of their body weight they would be switched to a diet that maintained that weight.

As expected, the people in all of the groups eating calorie-restricted diets lost weight. A number of other metabolic changes were also observed the dieters, but not in the people who ate normally. Fasting insulin levels dropped in all of the dieters, and core body temperature decreased in the low-calorie and low-calorie-plus-exercise groups, but not in the very-low-calorie group.

Based on previous research, these changes are believed to be signs that the aging process has slowed down. Resting energy output also decreased in the dieters, as did measures of cellular damage, adding to the evidence that the dieters aged less during the study period than the nondieters.

Dr. Michael Mundy, a chiropractor interested in human evolution and health, thinks that these results help to confirm the theory that we would be healthier if we ate as our earliest ancestors did. “We are tremendously overfed in modern society. Humans are designed to be hungry more of the time than we might prefer,” said Dr. Mundy. “Living in a time when food is always accessible, we rarely experience hunger, but studies like this one begin to show us that we could be healthier and live longer if we ate less and were hungry more.”

The hope that eating fewer calories could slow down aging might inspire some overweight people to stick to their diets, but the true beneficial and detrimental effects of calorie restriction over many years—or a lifetime—are far from clear. “Like all exciting short-term small studies, while it is tempting to shout, ‘This is the answer!’ you cannot predict the effects (positive or negative) to study subjects over a longer period of time,” said Mary Choate, a registered dietician and food and nutrition educator. It is also not clear whether the effects would be the same for people who are not overweight. Choate added, “What we can hope is that this research might eventually lead to more understanding about the aging process.”

(JAMA 2006;295:1539–48)

Maureen Williams, ND, received her bachelor’s degree from the University of Pennsylvania and her Doctorate of Naturopathic Medicine from Bastyr University in Seattle, WA. She has a private practice in Quechee, VT, and does extensive work with traditional herbal medicine in Guatemala and Honduras. Dr. Williams is a regular contributor to Healthnotes Newswire.

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