Curtailing calories on a schedule yields health benefits

Near-fasting for 5 days a month reduces body fat, study finds

soup high in fat

CALORIE CUTTER  Eating a very low-calorie diet with little protein but high fat for five days in a row each month can have a positive impact on health, a new study suggests. 


Diet smarter, not longer.

Slashing your food intake for just five consecutive days a month can yield a bounty of health benefits, according to a new study led by researchers from the University of Southern California. This briefer approach to caloric restriction, a severe form of dieting, challenges previous research that dieters might need to tighten their belts as often as twice a week to see positive effects.  

The team fed mice and humans a “fasting-mimicking diet,” a low-calorie, high-nutrition plan designed to trick cells into thinking they were fasting. The faux fasting periods lasted a few days and were followed by cycles of eating as much and as often as subjects wanted. The results appear online June 18 in Cell Metabolism.

Biogerontologist and study coauthor Valter Longo says the results show “that you can have a smart diet, a diet that can push all the right buttons,” without the severity seen in other caloric-restriction regimens.  

Mice lived about 11 percent longer (although this trend disappeared in very old mice), had fewer indicators of inflammation and cancer and saw a host of other benefits. Most notably, their brains grew more nerve cells, even when elderly.

fasting data
TRIPLE PLAY Researchers fed mice and humans a diet meant to trick cells into thinking they were fasting, leading to multiple health benefits. Yeast fasted using a slightly different protocol but still saw increased life spans and stress resistance. Brandhorst et al/Cell Metabolism 2015
Humans had reduced levels of C-reactive protein, an indicator of inflammation and cardiovascular disease, lost fat and gained lean muscle after eating the low-protein, high-fat diet. The diet, which consisted of about 1,100 calories on the first day and 725 calories a day for the next four, triggered a 3 percent loss in body weight, on average. Information about the exact foods participants ate is proprietary.

The human trial was small —just 19 dieters —and short, lasting three months. Mice ate the diet for roughly half their lives for eight days a month rather than five.

In many studies, caloric restriction has been shown to extend life span and improve health in certain organisms, but other research has produced conflicting results (SN: 1/24/15, p. 6, SN Online: 7/30/14), and scientists still aren’t sure how it works. But this study hints that the rest periods between bouts of dieting, not the time spent cutting calories, may play an important role in nerve cell growth in mice, says Mark Mattson, a neuroscientist at the National Institute on Aging in Baltimore, Md., who wasn’t involved in the study. In his own research, Mattson has found that fasting can yield nerve cell regeneration in the mouse brain, but his mice endured a much stricter fasting regimen of little to no food every other day. He says this new study shows the importance of the refeeding and recovery periods. “That was new and very interesting.”

Editor’s Note: This story was updated July 7, 2015, to clarify that most but not all of the researchers in the study were affiliated with the University of Southern California.

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