Cutting the calories really can help you live longer, according to researchers.
A study found that reducing calorie consumption was beneficial in older adults, but not in the young.
Calories are a measure for the amount of energy in food or drink. When people eat too many, the body stores the excess as body fat which can lead to weight gain.
For a while, scientists have been divided on the impact of dieting on ageing.
In a 2009 study, researchers at University of Wisconsin-Madison found there were significant benefits in survival and reductions in cancer, cardiovascular disease, and insulin resistance for monkeys that ate less than their peers.
But three years later the National Institute on Ageing (NIA) found no significant improvement in lifespan, although they added that it did help improve health.
“These conflicting outcomes had cast a shadow of doubt on the translatability of the caloric-restriction paradigm as a means to understand ageing and what creates age-related disease vulnerability,” said Associate Professor of Medicine Rozalyn Anderson at UW-Madison.
To settle this persistent scientific controversy, the competing scientists worked together.
In the new study, involving monkeys, they concluded that eating less was beneficial in older adults but not the young and they should eat a natural diet rather than processed “junk” foods with high sugar levels.
They also discovered that females are less vulnerable to adverse effects of being overweight than males.
The study re-analysed data gathered over many years involving nearly 200 monkeys to establish why the studies showed different results.
It found the animals in the two studies had their diets restricted at different ages.
Eating less was beneficial in adult and older primates but not beneficial for younger animals, which contradicted research in mice suggesting that starting a low calorie diet at a young age was better.
There was also a difference in how much the two groups of monkeys ate.
In the NIA study, the control monkeys ate less than the Wisconsin control group and this lower food intake was associated with improved survival compared to the Wisconsin controls.
It seemed small differences in food intake in primates could meaningfully affect ageing and health.
The monkeys also consumed different diets. The NIA monkeys ate naturally sourced foods and the UW-Madison monkeys ate processed food with higher sugar content.
The UW-Madison control animals were fatter than the control monkeys at NIA, indicating that at nonrestricted levels of food intake, what is eaten can make a big difference for fat mass and body composition.
There were also key sex differences in the relationship between diet, adiposity (fat) and insulin sensitivity, where females seem to be less vulnerable to adverse effects of adiposity than males.
The researchers noted this new insight appears to be particularly important in primates and is likely translatable to humans.
Professor Anderson added: “The upshot of the report was that caloric restriction does indeed seem to be a means to affect ageing.
“However, for primates, age, diet and sex must all be factored in to realise the full benefits of lower caloric intake.”
The study was published in the journal Nature Communications.