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Does fasting on alternate days work? A new study weighs in

5/8/2017, 6 a.m.
Whether you watch what you eat by counting your daily calories or practicing intermittent fasting, either approach can be effective ...
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— "We know daily calorie restriction -- if you have to count your calories everyday and all that -- it's a tough one. I think that there's some hope that this alternate-day fast, or modified fast, would be a better or easier strategy, but ... the dropout rate is kind of alarming," Ravussin said.

Varady said that, before the study, she thought the alternate-day fasting would be an easier diet to adhere to because it allowed for a "break" from dieting everyday.

"We were a little bit shocked to see that it was actually the calorie restriction group that seemed like they could stick better to their daily calorie goals. Whereas the alternate-day fasting group, they were kind of wavering," said Varady, who authored a book about alternate-day fasting called "The Every-Other-Day Diet."

"Instead of eating the 500 calories on the fasting days they were eating a couple hundred calories more on those days," she said.

Varady is already hoping to conduct follow-up research to track the various diets over a longer period of time, she said.

In the future, she would like to explore whether allowing study subjects to voluntarily opt to join either a fasting or calorie restriction group might influence study results.

'Not one diet fits everyone'

All in all, the new study showed that alternate-day fasting may be difficult to follow, but can be effective in reducing obesity, said Valter Longo, a professor at the University of Southern California and director of the university's Longevity Institute. He was not involved in the study.

However, "because it requires a major effort every other day, it is unlikely to be applicable to the great majority of the obese population, particularly in the absence of the close monitoring carried out in the clinical study," Longo said.

For overweight or obese adults who might be interested in alternate-day fasting as a weight loss approach, Varady advised to take the time to really determine whether it is the best option.

"Alternate-day fasting doesn't seem to work very well in people who are frequent snackers. People who need to eat every two hours, they don't tend to fare well on this diet, whereas people that just naturally tend to go a long period of time without eating, like four to five hours ... those people actually tend to do much better," Varady said.

"I really think people just need to find what works for them," she said. "Not one diet fits everyone."

Additionally, fasting potentially could be harmful for people with certain health conditions, such as diabetes -- so consult your doctor before attempting any major changes in your daily diet, such as alternate-day fasting.

"I don't think there's anything magical to the diet at all," she said about alternate-day fasting. "I think it's just another way of tricking people into eating less food or helping people to kind of monitor how much food intake there is, or how much food they're taking in."