Reducing daily calorie intake by a fifth has been shown to extend the lives of monkeys by 10 per cent, according to research at the University of Wisconsin.
During the study, published in the journal Nature Communications, a group of middle-aged rhesus monkeys were prevented from eating between 5pm and 8am.
Compared with those on a normal diet, this was found to increase their lifespan by 10 per cent on average, as long as the diet was started in later life, once the monkeys were in their teens.
The researchers say that calorie restriction extends life by preventing fatal diseases such as dementia and cancer. They say that their findings are relevant to humans, who share 93 per cent of the same genes.
The study’s lead author, Professor Rozalyn Anderson, said: ‘Cutting your calories delays ageing, probably because the body uses energy from food differently to become more resilient.
‘By targeting ageing itself we could, instead of fighting cancer or cardiovascular disease individually, target the full spectrum of disease simultaneously.
‘The low-calorie intake diet worked in the rhesus monkeys in their teens and 20s, but not in monkeys started on the diet early in the pre-teen years. This shows it may be better for people too if started in later life,’ she said.
This cohort study looked at the impact of reduced calorie levels on the survival and health of rhesus monkeys. This was done by comparing a calorie-restricted group to a control group at two separate institutions.
Previous studies in rodents suggested that calorie restriction was of benefit in terms of longer life span if started in childhood.
This study found that reducing caloric levels by 30 per cent seemed to lead to increased lifespan and a later onset of chronic disease.
Control group monkeys had twice the rate of death when compared to the calorie-restricted groups. Control group monkeys also had twice the rate of chronic disease. Calorie restricted monkeys also seemed to live on average two years longer.
This study had a number of flaws which affect applicability to human subjects.
The macronutrients were drawn mainly from processed sources that do not constitute the reality of the human diet. One would expect, in the absence of caloric restriction, that this would have deleterious effects on health.
The two calorie-restricted groups differed in the composition of the carbohydrate portion of their diets, with one group eating seven per cent of carbohydrates from sucrose while the other consuming 45 per cent of carbohydrates from sucrose.
It is not clear if intermittent fasting, itself shown to have positive physiological effects that may improve longevity, was being practised alongside calorie restriction.
Furthermore, it is not clear if physical activity was hampered by the degree of calorie restriction. If so this would have a detrimental effect on health. Exercise is a potent insulin sensitiser, and insulin resistance is steadily being shown to be a contributor to many human diseases. A lack of exercise would diminish any improvements seen in fasting blood sugar and amount of body fat.
The divergence in characteristics of the study subjects in the two calorie-restricted groups means that the conclusions based on survival may not be as accurate as they could be.
Take-home message: calorie restriction in rhesus monkeys may be useful in perpetuating health. In human subjects it is associated with constant hunger, rebound weight loss, breakdown of muscle tissue and lowered metabolic rate.