Eat Less - Live Longer
By Charlene Laino
"Severe caloric restriction does not undermine human health, as long as people receive adequate nutrition,"
ANAHEIM - Eat less and you may live longer. Long known to hold true for rodents and other animals, the benefits of caloric restriction appear to extend to humans, according to the first scientifically controlled trial of men and women who consumed a low-calorie, high-quality diet for two years.
For more than 60 years, scientists have known that animals that eat less live longer, healthier lives. And now new research presented here Thursday shows that people who follow a low-calorie, yet nutrient-rich diet, also lower their risk factors for serious disease.
With only 2.5 years of follow-up, the data still aren't in on whether study participants actually added years to their life spans.
But men and women "on a low-calorie, high-quality diet experienced the same broad physiological improvements that we see on animals on such diets," said study author Dr. Roy L. Walford, professor of pathology at the University of California, Los Angeles. "Therefore, there is every reason to believe that the other effects seen in animals - retardation of aging, life extension and a sharp incidence in risk of disease - also apply to humans."
The new findings grew out of the experimental study known as Biosphere 2, in which four men and four women, including Walford, sealed themselves inside a closed ecological area from 1991 to 1993. The enclosure comprised seven biomes: rain forest, Savannah, ocean, marsh, desert, farm land and a habitat for humans and domestic animals. All organic materials, all water and nearly all air were recycled, and virtually all food was grown inside.
Over the course of their stay, the men lost an average of 18 percent of their total body weight; women, 10 percent. Most of the weight loss occurred during the first six months of their stay, Walton reported.
Average blood pressure decreased an average of 20 percent. And indicators for diabetes - glucose, insulin and glycated hemoglobin - dropped about 30 percent. Cholesterol was lowered from an average of 193 to 123, and triglycerides also improved, Walton reported at the annual meeting of the American Association for the Advancement of Science.
So just what is a low-calorie diet? "On average, about 1,800 a day," Walford says, "but coupled with intense physical activity to burn off those calories." During their stays in the Biosphere, participants exercised vigorously six days a week.
Also, it's not just a matter of eating less and working out more, he stressed. "If you took the average American's diet and just lowered it, to total 1,800 calories a day, most Americans would end up starving themselves nutritionally."
Rather, a low-calorie diet is chiefly, though not exclusively, vegetarian, he said. For the study, participants dined three times a day on the grains, legumes, bananas, papayas and fresh greens and vegetables grown inside Biosphere 2. The livestock they raised provided small quantities of goat meat, pork, chicken, fish and eggs.
While low-calorie diets have been criticized as being nutritionally unsound, Walford said this new work proves the opposite. "Severe caloric restriction does not undermine human health, as long as people receive adequate nutrition," he said. "Biosphere 2 proved that people on a restricted caloric intake will lower their risk factors for disease and can perform well physically and intellectually, even for two years in a challenging environment."
Dr. James M. Nelson, of the University of Texas Health Science Center in San Antonio, agreed. "Essentially, we've now seen the same beneficial effects in humans that we observed in rodents," he said. But just how caloric restriction might increase life span remains unknown, said Nelson. His own work points to a type of hormone known as a corticosteroid as the factor responsible. The hormone appears to enhance resistance to insults and toxins, he said, boosting the immune system.
Walford's findings also hold a warning for chronic dieters. In analyzing Biosphere participants blood samples, he found that traces of toxins - which build up in the fatty tissue after exposure to pesticides and other pollutants - fluctuated dramatically over the two years.
As the subjects lost a lot of weight in the first six months, their blood toxin levels increased, he said. "Fat is where you store toxic residues in your body," he explained. "As it drops, the loss of body fat rapidly leads to an increase of toxins the blood."
Then, as the participants "gradually cleared the byproducts from their circulatory systems, blood toxin levels gradually dropped over the next 1.5 years, and again increased upon re-exposure to the outside environment, after their return to the real world."
"The data suggests that alternating weight loss and weight gain - so-called yo-yo dieting - may harm the body by flushing toxic substances in and out of the bloodstream," Walford cautioned.