Does eating less help you live longer?

In laboratory animals, the effect of eating less on lifespan is well documented. In mice, a 40% reduction in calories increases average lifespan by 10 to 40%. The same pattern has been observed in yeast cells, worms and flies. But the human body is not a mouse, and that translation is precisely where the uncertainty begins.

In healthy humans, the direct effect on lifespan has not yet been measured. What has been measured: in a randomised study in which people ate roughly 14% less for two years, the production of new immune cells improved and age-related inflammatory markers fell. These are favourable intermediate outcomes, but not proof that you will actually live longer as a result. In people with obesity and diabetes, randomised research showed a 15% lower mortality with calorie reduction. Whether this also applies to healthy people is unknown.

Not only how much you eat, but also when you eat, appears to matter. Eating patterns aligned with the biological clock and forms of intermittent fasting (in which you eat nothing for part of the day or week) confer health benefits, even when the total number of calories does not decrease. The evidence on this is promising but still limited in humans. Something else that stands out: not all calories are equal. Less protein in your diet, and specifically less of the amino acid methionine, extends lifespan in laboratory animals. In humans, the indications for this effect are indirect.

An important mechanism behind the positive effects is autophagy: the process by which cells clear out and recycle damaged material. Eating less activates this process. But going too far is a risk: with prolonged and very severe calorie restriction, this clearing process can become overactive and damage cells. In animals, a 40% calorie reduction also caused disadvantages for growth, reproduction and immune defence. The boundary between beneficial and harmful has not yet been precisely mapped in humans.