Can Eating Less Forestall Aging?

In a recent study, Labrador retrievers fed 25 percent less food than controls lived longer and were free of chronic disease for more of their lives. Previous research proved that rats fed less live longer. With this new study, scientists have shown that restricting calories works to extend life in large mammals as well. This increases hope that the same holds true for humans.

A team of researchers from the Nestle Purina Pet Care Company, University of Pennsylvania, University of Illinois, Cornell University, and Michigan State University fed 24 dogs just enough to maintain their ideal body weight. Twenty-four more dogs were fed 25 percent fewer calories. The median life span (age at which half the dogs died) for dogs fed less was 13 years. Dogs fed more lived just over 11 years.

Animals fed less not only lived longer, but lived longer without disease. Osteoarthritis was the most commonly diagnosed disease. Eventually, 43 of 48 dogs developed it; 19 in the control group and 16 in the calorie-restricted group required treatment. The age when dogs required treatment differed significantly. Controls needed treatment at about 10 years of age. Dogs fed less staved off treatment until age 13.

Other results revealed that dogs fed less weighed less and had less body fat and lower triglyceride levels than controls. Although dogs eating less attained lower muscle mass and bone density over their lives than control dogs, they preserved their muscle and bone for a longer time than controls—signs of healthy aging. Also, dogs fed less showed no signs of nutritional deficiency.

These results, although positive, offer no definitive answers about how a lower calorie diet extends life. Disease patterns in humans link high body fat with increased chronic disease and death. Studies in rats, however, have raised the idea that the amount of body fat is less important to longevity than the amount of food eaten. Genetically obese rats that eat less food outlive normal-weight rats that eat a normal diet. Limiting calories may cause positive changes in the body that go beyond preventing diseases that accompany high body fat.

The National Institutes of Health (NIH) are conducting studies in primates and plan trials with people for more answers. In research on primates, preliminary data look promising. Monkeys fed 30 percent fewer calories are living longer and healthier lives than controls. Translated into human diets, this equals about 1,120 daily calories for women and 1,540 for men, based on U.S. Department of Agriculture (USDA) recommendations that sedentary women eat about 1,600 calories a day and inactive men eat about 2,200.

In the upcoming NIH study with people, volunteers will cut calorie levels by 20 to 30 percent for up to 3 years. To help them comply with the restricted diet, study participants will, at first, eat food prepared and served at the research site. Metabolism, body temperature, blood sugar, triglyceride levels, and other factors will be monitored to see how body chemistry changes in response to restricting calories.

Findings from the study may reveal that a lower calorie diet extends life, and biochemical processes that forestall aging may be uncovered. This work will advance scientific knowledge, but much work still lies ahead to reverse current eating trends.

The full report of the dog study can be found in the May 1, 2002 issue of the Journal of the Veterinary Medical Association. s