Scientists have long known a fairly reliable way to extend life span in rodents and other lab animals: reduce the amount of calories they eat by 10 per cent to 40 per cent.

This strategy, known as caloric restriction, has been shown to increase the life span of various organisms and reduce their rate of cancer and other age-related ailments. Whether it can do the same in people has been an open question. But an intriguing new study suggests that in young and middle-aged adults, chronically restricting calorie intake can have an impact on their health.

In the new study, which was funded by the US National Institutes of Health and published this month in the Lancet Diabetes & Endocrinology, researchers looked at a group of 143 healthy men and women who ranged in age from 21 to 50. They were instructed to practice caloric restriction for two years. They could eat foods they wanted so long as they cut the total amount of food they ate, with the aim of cutting the calories they consumed by 25 per cent.

Many did not achieve that goal. On average the dieters managed to slash about 12 per cent of their total calories, or roughly 300 calories a day, the amount in a large bagel or a few chocolate chip cookies. But the group saw many of their cardiovascular and metabolic health markers improve, even though they were already in the normal range.

They lost weight and body fat. Their cholesterol levels improved, their blood pressure fell slightly, and they had better blood sugar control and less inflammation. At the same time a control group of 75 healthy people who did not practice caloric restriction saw no improvements in any of these markers.

Metabolic health

Some of the benefits in the calorie restricted group stemmed from the fact that they lost a large amount of weight, on average about 16lb (7kg) over the two years of the study.

But the extent to which their metabolic health got better was greater than would have been expected from weight loss alone, suggesting that caloric restriction might have some unique biological effects on disease pathways in the body, said Dr William Kraus, the lead author of the study and a professor of medicine and cardiology at Duke University.

“We weren’t surprised that there were changes,” he said. “But the magnitude was rather astounding. In a disease population there aren’t five drugs in combination that would cause this aggregate of an improvement.”

The new study provided evidence of just how difficult calorie restriction can be. The study participants went through an intensive training programme where they learned to cook low-calorie meals, attended group sessions and had regular check-ins with nutrition experts. Still, they were not able to meet even half the goal of a 25 per cent cut in calories. And as anyone who has dieted knows, keeping the weight off long term can be the hardest part.

Legacy effects

Kraus at Duke said that he hoped to study the participants again in 10 years to see if the benefits of the caloric restriction experiment persist, a phenomenon known as legacy effects, which can occur with intense exercise training and other health interventions.

But for now he said that one takeaway for the public is that people can benefit from shaving as little as 300 calories a day from their diets.

“It’s not that hard to achieve that amount of caloric restriction,” he said. “That’s essentially an after-dinner snack.” – New York Times

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