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Study casts doubts on alternate-day fasting diet

Alternate-day dieters ate more on fasting days than those on conventional diets

Mark Gould

Tuesday, 02 May 2017

Alternate-day fasting diet regimes are harder to stick to than conventional weight loss regimes, according to new research.*

Writing in the journal JAMA Internal Medicine, Krista Varady from the University of Illinois at Chicago and colleagues from four US institutions, recruited 100 overweight or obese participants, 86% of whom were women, and randomly allocated them to one of three regimes: eating as normal, daily calorie counting and an alternate-day fasting diet.

For the first month, all participants ate as normal, after which they spent six months on their allocated diet. In the fasting diet, participants consumed 25% of their normal daily calorie intake on the “fast” day, and 125% the following “feast” day, while the calorie-restricted group consumed 75% of their normal calorie intake every day. The third group made no changes to their typical diet.

The results reveal that, compared to those who didn’t change their diet, those on the fasting diet and those on the calorie-restricted diet had on average lost roughly the same amount of weight after six months.

By the end of the study, those who had fasted and those who undertook a daily diet were 6% and 5.3% lighter respectively than those who had not changed their diet. The results held when factors such as the sex and ethnicity were taken into account.

“We thought that it would be easier to stick to alternate-day fasting, just because you get that day off every [other] day where you don’t have to diet,” said Ms Varady. “We were really just expecting the traditional [daily diet] group to cheat a lot more.”

The team said the findings might be down to a greater than expected difficulty in sticking to the fasting diet, with data showing they typically ate more calories than designated on the fast days and fewer than designated on the feast days.

“We found that around half the people in the alternate-day fasting group had a hard time sticking to it,” said Varady.

The authors admit that the study had limitations due to the small sample size and that only 69% of participants completed the study.

Ms Varady concludes that there is no one-size fits all approach to dieting. “Some people can stick to alternate-day fasting better, some people can probably stick to calorie-restriction way better,” she said. “People just need to figure out which one is better for them.”


* Trepanowski JF, Kroeger CM, Barnosky A, et al. Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults. A randomized clinical trial. JAMA Intern Med. Published online May 1, 2017. doi:10.1001/jamainternmed.2017.0936

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