A big drop in metabolism Janine Zdemir / EyeEm

Severely cutting the calories you eat may expand your lifespan, and now we have an idea of why. A study in which people ate 15 per cent fewer calories than usual has found that eating a lot less has big effects on what happens to the body during sleep.

Many studies have found that calorie restriction extends the lifespan of animals such as worms, flies, mice and even monkeys. The findings have prompted a few thousand people to choose to eat around 15 to 18 per cent fewer calories than the daily recommended limit, in the hope that they’ll live longer and healthier lives, and there is some evidence that such people have better blood cholesterol and glucose levels.

To investigate this further, Leanne Redman of Pennington Biomedical Research Center in Louisiana and her colleagues randomly assigned normal or calorie restricted diets to 53 adults. For two years, 34 of these people ate 15 per cent fewer calories, while the others ate as much as they wanted.


The calorie-restricted regime seemed to cause some interesting effects. In the second year of the study, those eating fewer calories showed a dramatic drop in their night-time metabolic rates, and a small but significant drop in their night-time body temperature. “Metabolism measured during sleep was reduced by 10 per cent,” says Redman.

Less cell stress

Analysing blood samples revealed that these people also experienced a 20 per cent drop in cellular oxidative stress – damage to cells caused by the byproducts of metabolism. DNA and cell damage caused by oxidative stress are thought to be key hallmarks of ageing.

Redman thinks that a low-calorie diet may push the body to have a lower resting metabolic rate. This may be an evolutionary mechanism to save energy when food is scarce, as is seen in animals that hibernate.

“This study is the first to show that humans respond to calorie restriction by a reduction in resting metabolic rate,” says Luigi Fontana of Washington University in Missouri. But he says that this drop in metabolism isn’t necessarily what causes increased longevity in animals on calorie restricted diets. He thinks changes in how cells sense the availability of food are likely to be more important.

However, even if it’s found to work well in people, calorie restriction isn’t for everyone. At first, it requires very careful meal planning, and side effects can include a loss of libido and feeling cold.

Journal reference: Cell Metabolism, DOI: 10.1016/j.cmet.2018.02.019

Read more: Calorie restriction diet extends life of monkeys by years