PhotoIf you’re a consumer who struggles with obesity or being overweight, then one of the first suggestions you’re likely to hear is that you should restrict the number of calories you consume each day. However, this can be a major test of willpower for some, and different fad diets have tried to come up with ways that allow consumers to lose weight while letting them eat what they want.

One of the newest strategies is called alternate-day fasting, where consumers are encouraged to eat whatever they want on one day and follow it up with a day of fasting where they only consume up to 25% of their usual calorie intake. This approach has increased in popularity and has even made its way into several diet books, with proponents calling it a superior way to lose weight. But does it work?

Researchers from the University of Illinois at Chicago set out to answer that question and found that the diet might not be all it’s cracked up to be. After conducting a one-year randomized clinical trial, they found that participants who followed an alternate-day fasting diet did not experience any additional weight loss when compared to those who dieted normally.

"The results of this randomized clinical trial demonstrated that alternate-day fasting did not produce superior adherence, weight loss, weight maintenance or improvements in risk indicators for cardiovascular disease compared with daily calorie restriction," the researchers said.

Trouble sticking to the diet

The study included 100 obese participants between the ages of 18 and 64 that were assigned to one of three groups for one year. One group followed an alternate-day fasting diet where participants consumed only 25% of their calorie needs on “fast” days and 125% of calorie needs on “feast” days; one group restricted their calorie intake to 75% of their caloric needs every day; and one group was given no intervention.

At the beginning of the experiment, the researchers expected that those following an alternate-day fasting diet would be able to adhere to their diet more easily, achieve greater weight loss, and reduce their risk for cardiovascular disease. However, the end results showed that these participants had the most trouble following their diet plan.

“Participants in the alternate-day fasting group ate more than prescribed on fast days, and less than prescribed on feast days, while those in the daily calorie restriction group generally met their prescribed energy goals,” the researchers said.

Not “superior”

In addition to not losing any more weight than participants in the calorie restriction group, the researchers found that those in the alternate-day fasting group were more likely to drop out of the study.

“Alternate-day fasting has been promoted as a potentially superior alternative to daily calorie restriction under the assumption that it is easier to restrict calories every other day. However, our data from food records. . . indicate that this assumption is not the case. Rather, it appears as though many participants in the alternate-day fasting group converted their diet into de facto calorie restriction as the trial progressed,” the researchers said.

“Moreover, the dropout rate in the alternate-day fasting group (38%) was higher than that in the daily calorie restriction group (29%) and the control group (26%). It was also shown that more participants in the alternate-day fasting group withdrew owing to dissatisfaction with diet compared with those in the daily calorie restriction group. Taken together, these findings suggest that alternate-day fasting may be less sustainable in the long term, compared with daily calorie restriction, for most obese individuals.”

The researchers point out that some individuals may still prefer alternate-day fasting over more conventional dieting techniques, but their study does put into question whether or not this new technique truly is “superior.”

The full study has been published in JAMA Internal Medicine.


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