Can cutting calories boost lifespan? Likely, but the jury is still out

Restricting calories could improve health and prevent the onset of age-related diseases, a recent study suggests. Two research teams from the University of Wisconsin-Madison and the National Institutes on Aging (NIA) revealed one component to losing weight and living longer may be a calorie restriction diet.

Researchers from both institutions found cutting calories by about 11 per cent for two years reduced inflammation and risk factors for heart and metabolic disease in monkeys by the end of the study, but they had low bone density. The diet has been the subject of some controversy, with sceptics questioning whether it's really effective.

Despite their shorter life spans, rhesus monkeys were used because they develop and age very similarly to humans. They get gray hair, saggy skin, and even acquire the same diseases humans do, like cancer, diabetes, and dementia.

Previous research from UW-Madison suggests there are significant benefits in survival and reduction in cancer, cardiovascular disease, and insulin resistance from limiting caloric intake. UM-Madison kept a group of these primates under observation in which half were allowed to eat whatever they want.

The other group was fed nutritious food, but calories were cut down by about 30 per cent compared to their counterparts. Over the course of 25 years, researchers found monkeys on unrestricted diets had a three times greater risk of age-related death and diseases than those on regulated calories.

But a similar NIA study noted there was no significant improvement in survival from restricted food intake, though a trend toward improved health could be noticed.

"These conflicting outcomes had cast a shadow of doubt on the translatability of the caloric-restriction paradigm as a means to understand aging and what creates age-related disease vulnerability," said Rozalyn Anderson, UW–Madison associate professor of medicine, in a statement.

This prompted both research teams to work together in competing laboratories to review data from over the years, including data of 200 rhesus monkeys and the influence of calorie restriction diet plans on health and longevity. The collaboration sought to resolve the controversial outcome in aging research, and also how exactly calorie restriction works in primates. The role of calorie restriction in aging and disease was undeniable, but its effects on primates depended on factors like diet, age, and sex.

The findings revealed the conflicting results were due to the monkeys being put on calorie restriction diets at different ages. Adult and older primates were more likely to benefit from these diets in terms of health and longevity, compared to younger animals. Food intake was also inconsistent among the test and control groups; acknowledging small differences in food intake in primates can affect aging and health. Moreover, the food quality fed to the monkeys varied between the two studies. Monkeys in the NIA study were fed naturally-sourced foods, while those in the UW-Madison study ate processed foods with higher sugar content. Evidently, this led to a fatter control-group at UW-Madison.

Overall, moderate calorie restriction (about 30 per cent), was effective, but severe caloric reductions (50 per cent), did not benefit the monkeys' health. The monkeys in the UW-Madison trial lived longer than the controls; with males living about two years longer, and females living about six years longer. They also showed lower rates of cancer and heart disease.

Meanwhile, caloric restriction didn't have a specific effect on the NIA monkeys' lifespan - both the dieting and control monkeys survived a significantly long time, some more than 40 years.

It's obvious if monkeys are fed a more Western diet and put on calorie restriction, they will reap health and survival benefits. Both studies do conclude limiting caloric intake could improve health and prevent the onset of age-related diseases. It remains to be seen whether calorie restriction diets can improve survival.

It's also still unclear if this research on monkeys could be applied to humans.