When it comes to human weight and its effect on life span, opinions change about as often as the latest fad diet. A few decades ago, thin was not only “in,” it was thought to be the secret of youth. Then scientists concluded that being too thin or too heavy could subtract years from life. This year, a study revealed that people who enter adulthood with a normal body mass index, then became slightly overweight, but not obese, lived longer.
One reason it’s difficult to pin down an answer is that people live such long lives that it’s nearly impossible to study humans across an entire life span.
With dogs, it’s different. Labrador retrievers, for example, have a life expectancy of about 10 to 12 years. That’s why researchers were able to conduct a groundbreaking, 14-year study following 48 Labrador retrievers throughout their entire lives to discover that keeping dogs lean can add, on average, almost 2 years to their life spans.1
Tracking dogs for a lifetime
The study started with 48 Labrador retriever puppies. All dogs received the same diet, but half of the dogs were fed 25 percent less food than the other dogs. Even though some dogs received less food, researchers made sure the group wasn’t missing any nutrition.
At the end of the study, the median life span for dogs who ate less was 13 years, compared to 11.2 for the dogs that were fed more — that’s a difference of 1.8 years. It was the first longitudinal study to show that dietary restriction, without malnutrition, could extend canine life span.
Later onset of arthritis
Feeding restriction didn’t have a negative impact on dogs in terms of how their skeletons matured, bone structure or metabolism,2 but dogs that were kept lean experienced joint-health advantages.
By two years of age, the incidence of hip dysplasia in the dogs fed less was half that of the full-fed dogs. The severity of the condition was much less for the lean dogs, as well.3
The onset of hip arthritis for these dogs was later in life, too. The median age when hip arthritis could be recognized on X-rays was 6 years for the full-fed dogs, while lean dogs didn’t show evidence of arthritis until 12 years of age. That’s six extra years of chasing balls and going on hikes, presumably without the pain of arthritis to hold them back.
The same was true for arthritis in other joints. At 8 years of age, only 10 percent of lean dogs had osteoarthritis in two or more types of joints, compared to 77 percent of the full-fed dogs.4
Other health benefits
As dogs age, they’re more likely to suffer from age-related diseases. Compared to the full-fed dogs, lean dogs showed greater insulin sensitivity, which helps stave off diabetes. Their immune systems were better able to fight off infections, as well. This could be part of the reason why keeping dogs lean seems to delay the onset of age-related diseases.1-3
The mean age at which half of the lean dogs required treatment for a chronic condition was 12 years of age, compared to 9.9 years for the full-fed dogs.
The lesson for pet parents with overweight dogs is this: Weight loss can help improve their health, quality of life and even extend their life spans. That said, you shouldn’t just reduce the quantity of your dog’s food by 25 percent, because that can lead to nutritional inadequacies. Instead, work with your veterinarian to devise a plan to help your dog lose weight — and stay lean — in a healthy way.
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- Kealy RD, Lawler DF, Ballam JM, et al. Effects of diet restriction on life span and age-related changes in dogs.J Am Vet Med Assoc 2002; 220:1315-1320.
- Lawler DF, Larson BT, Ballam JM, et al. Diet restriction and ageing in the dog: major observations over two decades.Brit J Nutr 2008; 99(4):793-805.
- Smith GK, Paster ER, Powers MY, et al. Lifelong diet restriction and radiographic evidence of osteoarthritis of the hip joint in dogs.J Am Vet Med Assoc 2006; 229(5):690–693.
- Kealy RD, Lawler DF, Ballam JM, et al. Evaluation of the effect of limited food consumption on radiographic evidence of osteoarthritis in dogs. J Am Vet Med Assoc 2000; 217(11):1678-1680.