Eating less results in longer lives, a 14-year CU dog-diet study confirms By Lissa Harris
Seventy years after a classic Cornell nutritional study showed that cutting rations dramatically prolongs rats' lives, nutrition scientists have come up with even more evidence of the benefit of slender diets: A recently completed 14-year study found that dogs forced to eat 25 percent less than their littermates of the same balanced diet lived significantly longer and suffered fewer canine diseases. In an age of increasing incidence of obesity among Americans, "maybe it's time we watched what the rats and the dogs are eating," advises George Lust, a Cornell professor of veterinary medicine and a collaborator in the experiment with dogs, sponsored by the Nestlé Purina Pet Care Co. A specialist in bone and joint diseases in animals, Lust saw the underfed dogs incurring much less canine hip dysplasia (CHD) and subsequent osteoarthritis, compared with dogs that were fed the portions indicated on the pet food packages.
The dogs on reduced rations also lived nearly two years longer. In animal nutritionist Clive McCay's 1930s' demonstration of the power of portion control on health, rats on an experimentally reduced diet lived half again as long as rats on "normal" diets. His findings with rats are well known to every nutritionist, but determining the implications for human health has remained a challenge. The dog study comes closer, providing the strongest evidence yet that diet restriction confers benefits of health and longevity on larger mammals. While the benefits of diet reduction have been demonstrated in animals from chickens to single-celled organisms, dogs are our closest evolutionary relatives in which a reduced diet definitively has been shown to enhance health and lengthen life. The ambitious dog study was led by researchers at Nestlé Purina, and included scientists at Cornell, the University of Illinois, Michigan State University and the University of Pennsylvania. Results of the study were published in the
Journal of the American Veterinary Medical Association in May.
The study also was the focus of a September symposium in St. Louis, sponsored by Nestlé Purina, called "Advancing Life Through Diet Restriction." In the study, 24 pairs of Labrador retriever siblings between 6 and 8 weeks of age -- matched by sex and weight-- were selected, with one of each pair assigned to eat 25 percent less food than its sibling. The dogs were a part of the study from the time they were weaned until they died, and their health was closely monitored throughout their lives. The median age of dogs in the reduced-diet group, the researchers found, was 13 years -- 1.8 years longer than the median age of dogs fed a normal diet. As a result of genetic factors, Labradors are predisposed to develop CHD and osteoarthritis. Lust, a professor of physiological chemistry at the James A. Baker Institute for Animal Health at Cornell, followed the development of the disease in the 48 dogs in the study. He found striking effects of diet on the progression of the disease, even in young animals. "It was dramatic. In the control group of 24 dogs -- the well-fed dogs -- 16 had CHD at 2 years of age, and eight were normal," Lust said. "Of the 24 dogs in the restricted diet group, only eight had CHD and 16 were normal."
The reduced diet also was found to reduce the risk of developing osteoarthritis, which generally results from CHD and is one of the most common sources of chronic pain treated by veterinarians. It is also the most common form of arthritis in humans, affecting over 20 million people in the United States. Only six dogs on the reduced diet developed osteoarthritis of the hip by age 10, while 19 of the dogs in the control group developed the condition. And for dogs with CHD and on reduced rations, the diet decreased the odds of developing osteoarthritis by 57 percent. Similar studies involving primates are under way at the University of Wisconsin. Because of the long life span of monkeys, however, it will be years before the results of those studies are known.
December 12, 2002