Writing in the Wall Street Journal this week, Shirley Wang explores research behind the latest fad diet—intermittent fasting—and what it may do for the human body.
Wang profiles several people who have lost weight and "cured" their diabetes by regularly abstaining from eating. Some follow the popular 5:2 Diet—which recommends eating normally on five days and restricting calories on two days—while other dieters have created their own fasting plans, such as eating one meal every 24 hours, or fasting every other day.
"It isn't clear whether the very-low-calorie element of the diet confers health benefits in humans, or if the diet simply helps people eat less and lose weight temporarily, like with daily calorie restriction," Wang writes, adding that very little research has been conducted on humans.
Fasting may improve cognitive abilities, muscle mass maintenance
Researchers at the National Institute on Aging (NIA) studied animals that fasted every other day and found that the diet improved their cognitive functioning and ability to maintain muscle mass. Animals on a restricted calorie diet did not reap such benefits. In earlier studies, NIA researchers found that fasting on alternate days improved or even reversed Alzheimer's-like conditions among mice and rats.
Fasting for periods as short as 16 to 24 hours seems to induce a state of mild stress on the body, during which the brain releases additional neurotrophic proteins that help stimulate the growth of neurons and other cells, according to NIA's Mark Mattson. Similar to the way exercise makes muscles stronger, fasting appears to make the brain strong, Mattson added.
Fasting more effective than calorie restriction
In a study of overweight women, University Hospital South Manchester researchers found that women who fasted on alternate days lost twice as much weight as those who simply restricted calorie intake.
Fasting on alternate days is successful as long as people do not overeat on "normal" days, according to fasting researcher Krista Varady of University of Illinois at Chicago. She added that her research has shown that fasters usually do not overeat on non-fasting days, eating just a bit more than average.
Fasters say they get used to the routine after about 10 to 30 days and then cannot actually eat as much as they used to, Varady says.
"We think that once the people get adjusted to the diet—it's a big change to a diet—it is easy to adhere to," Mattson says, adding, "If you know that tomorrow you can eat normally, you can make it through today" (Wang, Journal, 12/2).