By Dr. Becker
Results of a study that has been running for 25 years conclude that monkeys fed a reduced-calorie diet live longer than those who are able to eat as much as they want.
These findings add to a small but growing body of evidence that restricted diets prolong life in a range of species, including Labrador Retrievers.1
Restricted Calorie Diet Prolonged the Lives of Rhesus Macaques, Study Shows
In the study, which began in 1989 at the Wisconsin National Primate Research Center, 76 rhesus macaques were separated into two groups. The group one monkeys were allowed to eat whatever they wanted, presumably in whatever quantity they wanted, while group two was fed a diet 30 percent lower in calories.
Results showed that monkeys in group one were nearly twice as likely to die at any age as those in group two. Interestingly, in 2009, the same study reported that group two monkeys were less likely to die of age-related causes than group one monkeys, but that both groups had similar overall mortality rates at all ages. As it turns out, the 2009 findings did not reflect that calorie-restricted monkeys lived longer because at the time, too few monkeys had died to prove the point.
Rozalyn Anderson of the University of Wisconsin, who led the study states, “We set out to test the hypothesis: would calorie restriction delay aging? And I think we’ve shown that it does.”
Does Calorie Restriction Trigger a 'Biochemical Pathway That Promotes Survival'?
Another study involving mice also suggests that eating a restricted diet prolongs life,2 and according to the journal Nature, this study sparked speculation that restricting calories triggers a “biochemical pathway that promotes survival.” However, identifying the pathway, and establishing whether humans have it, remains a hotly debated topic. But Anderson believes the results of her study with macaques will affect the way in which people in geriatric clinics are treated ten years from now.
Scientists at the National Institute on Aging (NIA), who conducted their own study on monkeys in 2012, aren’t convinced:
“Are we seeing health benefits? Yes, but I don’t know that we're necessarily seeing survival benefits,” says Julie Mattison, a physiologist at the NIA.
“I think what we're arriving at is that the effects of calorie restriction on survival are very dependent on genetics, the environment and the effect on body weight, and probably the diet that you give the animals.”
Different Studies, Different Outcomes
According to Nature, composition of the monkeys’ diets and also their feeding regimen very likely made a significant difference. All the macaques in the Wisconsin study were initially fed “purified” pellets that contained almost 30 percent sugar, while the diet of the monkeys in the NIA study contained more whole grains and just 4 percent sugar.
And due to differences in the way the Wisconsin and NIA monkeys were fed, Nature speculates that the Wisconsin monkeys were heavier overall than the average for captive monkeys, whereas the NIA monkeys were lighter than average.
According to Wisconsin’s Anderson, the NIA study compared the results of a little calorie restriction vs. a lot of calorie restriction, which is why their results didn’t show a survival difference. But according to Mattison of the NIA, the calorie-restricted Wisconsin monkeys may have outlived the other group simply because they acquired fewer diseases linked to obesity, such as diabetes, rather than because they received a biochemical benefit from a restricted calorie diet.
According to Mattison:
“If you take an animal that's eating a whole bunch of sugar and cut out 30% of those calories, it's not surprising that they do a bit better, whereas we're taking an animal eating very healthy food and cutting back and not getting the same robust effect.”
What This Means for You and Your Pet
The researchers at both facilities have begun working together to evaluate their data to try to determine the influences of weight, genetics, diet composition, calorie count, and other factors of the monkeys’ environments.
Mattison of the NIA cautions that at this point in time, it’s not possible to say with any certainty how the monkey studies translate to human lifespans.
While the debate rages on about whether calorie-restricted diets are one of the keys to living longer, I think an important reminder to take away from these studies is that routinely overindulging pets with food and treats achieves the opposite result. I find it somewhat annoying we have to prove (on a population of captive animals) that keeping animals lean is healthier for them. I view this as common sense.
Feeding a balanced, whole food, species-appropriate diet in portion-controlled servings, and offering a few beneficial treats now and then, is in my experience the best way to help your beloved cat or dog enjoy a long, healthy life.