For the Labrador Retrievers in the study, the statistic translates into two years.

The Purina study was begun in 1987 and was completed in 2001. Dr. Dennis Lawler, who along with fellow Nestlé Purina scientist and principal investigator Richard Kealy, Ph.D. headed the research team. "What's exciting about this study is that, for the first time in a larger mammal, we proved that eating less resulted in longer life. That's pretty powerful stuff."

Dr. Gail Smith, study collaborator and professor of orthopedic surgery at the University of Pennsylvania School of Veterinary Medicine, says the study constitutes a one-of-a-kind body of work yielding profound benefits to veterinarians and clients.

"Purina invested 14 years in a scientific study that has already produced useful clinical information. And with continued analysis of accumulated data, the study promises to add to the body of scientific literature for years to come," he says. "The amount of data on canine body systems is enormous and the impact on the health and quality of life of our patients will be significant."

The 14-year study was conducted at the Purina Pet Care Center and compared 48 Labrador Retrievers from seven litters. The dogs were paired within their litters according to gender and body weight and randomly assigned to either a control or lean-fed group. The control group was fed ad libitum during 15-minute daily feedings, while the lean-fed group was fed 75 percent of the amount eaten by its paired littermates. All dogs consumed the same 100 percent nutritionally complete and balanced diets (puppy, then adult formulations) for the entire period of the study; only the quantity provided was different, the study says.

Dogs were weighed weekly as puppies, periodically as adolescents and weekly as adults. Beginning at 6 years of age, they were evaluated annually for body condition using the Purina Body Condition System, a standard used by veterinarians to evaluate body physique in pets. Other health indicators including body fat, lean body mass and bone mass, effective glucose and insulin use as well as serum cholesterol and triglyceride levels were measured annually.

Median life span was increased by 1.8 years, or 15 percent, in the lean-fed dogs compared to the control dogs. Median life span (age at which 50 percent of the dogs in the group had died) was 11.2 years in the control group compared to 13 years in the lean-fed group.

By age 10, only three lean-fed dogs had died, compared to seven control dogs. At the end of the 12th year, 11 lean-fed dogs were alive, with only one control dog surviving. Twenty-five percent of the lean-fed group survived to 13.5 years, while none of the dogs from the control group lived to that age.

In addition, the age when 50 percent of the dogs required treatment for a chronic condition was 12 years among the lean-fed dogs, compared to 9.9 years for the control dogs. The lean-fed group had lower serum triglycerides and triiodothyronine, as well as healthier insulin and glucose use.

"What we have learned from this study is that feeding less does not necessarily change what health problems dogs encounter, or what, ultimately, causes their death," Lawler says. "What it does change is when this occurs." This observation, he adds, is corroborated by the results of restricted feeding research in other species.

Dr. Aine McCarthy, director of professional communications for Nestlé Purina PetCare, says the study proves that lean dogs live longer and better lives, yet millions of dogs are overweight and obese.

"Because of the relationship ­ now proven ­ between lean or ideal body condition and good health, the concept of feeding to ideal body condition should be discussed with every pet owner," McCarthy says. "Veterinarians now have a powerful and important message they can deliver with confidence to their clients ­ along with data to back it up," she adds.