Going hungry for 5 days a month may improve your health.

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Five-day fasting diet could fight disease, slow aging

Fasting is all the rage. Self-help books promise it will incinerate excess fat, spruce up your DNA, and prolong your life. A new scientific study has backed up some health claims about eating less. The clinical trial reveals that cutting back on food for just 5 days a month could help prevent or treat age-related illnesses like diabetes and cardiovascular disease.

“It’s not trivial to do this kind of study,” says circadian biologist Satchidananda Panda of the Salk Institute for Biological Studies in San Diego, California, who wasn’t connected to the research. “What they have done is commendable.”

Previous studies in rodents and humans have suggested that periodic fasting can reduce body fat, cut insulin levels, and provide other benefits. But there are many ways to fast. One of the best known programs, the 5:2 diet, allows you to eat normally for 5 days a week. On each of the other 2 days, you restrict yourself to 500 to 600 calories, about one-fourth of what the average American consumes.

An alternative is the so-called fasting-mimicking diet, devised by biochemist Valter Longo of the University of Southern California in Los Angeles and colleagues. For most of the month, participants eat as much of whatever they want. Then for five consecutive days they stick to a menu that includes chips, energy bars, and soups, consuming about 700 to 1100 calories a day.

The food, produced by a company that Longo helped found (but from which he receives no financial benefit), is high in unsaturated fats but low in carbohydrates and proteins, a combination that may spur the body to restore itself and burn stored fat. Two years ago, Longo’s team reported that mice on the rodent version of the diet lived longer and exhibited other positive effects, such as lowered blood sugar and fewer tumors. They also presented preliminary data suggesting health benefits in humans.

Now, the researchers have completed a randomized clinical trial in which 71 people followed the fasting-mimicking diet for 3 months, while volunteers in the control group didn’t change their eating habits. Overall, the dieters lost an average of 2.6 kilograms (5.7 pounds), whereas the control group remained at the same weight, the scientists report online today in Science Translational Medicine. The calorie cutters also saw reductions in blood pressure, body fat, and waist size.

A 3-month trial can’t determine whether the diet increases longevity in people like it did in mice, which rarely survive beyond a couple years. But Longo notes that levels of insulin-like growth factor 1, a hormone that promotes aging in rodents and other lab animals, plunged in the low-cal group. And subjects who were at the highest risk for age-related illnesses also saw other indicators of malfunctioning metabolism go down, such as blood glucose levels and total cholesterol.

Longo says that this diet “treats” aging, the most important risk factor for killers like diabetes and cardiovascular disease. “It looks like you can go at the underlying problem rather than just putting a Band-Aid on it,” he says. In a follow-up trial, the team hopes to determine whether the diet helps people who already have an age-related disease—probably diabetes—or are susceptible to one.

Dieting is often hard, but 75% of the low-cal participants managed to complete the trial, notes gerontologist Rafael de Cabo of the U.S. National Institute on Aging in Baltimore, Maryland, who wasn’t involved with the work. The next step, says physiologist Eric Ravussin of the Pennington Biomedical Research Center in Baton Rouge, is to determine whether the diet also works in people “who are not as healthy as they used in this study.”

Research dietitian Michelle Harvie of the University Hospital of South Manchester in the United Kingdom adds that she wants to see longer studies confirm that the benefits persist and that people remain on the regimen. “We need to help a lot of people, but what if only 2% of them are willing to do this?”