Does eating less make animals, and people, live longer?

Sometimes in some animals, but the evidence is mixed, and for people it is still early. Calorie restriction means cutting energy intake below what the body needs without causing malnutrition; in ageing research that last part is the point. Its possible effects on body weight, longevity and age-related disease are an active area of research.

The cleanest hints come from animals. A calorie restriction diet has been shown to extend lifespan in some animals, and inhibiting a nutrient-sensing pathway called mTOR, through dietary restriction or the drug rapamycin, is one of the most robust ways of increasing lifespan in worms, flies and mice. That prompted attempts to develop drugs that mimic the diet, such as rapamycin and metformin.

Monkeys, though, split the field. A National Institute on Aging study begun in 1987 found that calorie restriction did not extend life or reduce age-related deaths in non-obese rhesus macaques, although it improved some health measures. A Wisconsin study, also started in 1987, showed the opposite on lifespan.

For humans, the honest summary is that it is unsettled. In the two-year CALERIE trial, adults who cut their calories by about 12% had lower cholesterol and other heart-risk measures, but the trial measured risk factors over two years, not lifespan. As of 2021, calorie restriction and intermittent fasting remain under preliminary research for their effects on disease and lifespan, and the risks of long-term restriction remain undetermined.