Intermittent fasting is ‘nothing special’ for weight loss

BATH, United Kingdom — Intermittent fasting approaches to weight loss such as alternate day fasting or the ‘5:2’ diet have exploded in popularity in recent years. Now, a new study is challenging intermittent fasting’s claim as the most effective weight loss avenue. Researchers from the University of Bath report that at the end of the dieting day there’s “nothing special” about the restrictive diet.

You’ve probably seen miraculous body transformations attributed to fasting on social media, or perhaps noticed a celebrity or two endorsing some variety of intermittent fasting. On the scientific side of things, however, research supporting intermittent fasting as a cut above all other traditional diets is lacking.

Consequently, the team at UB set up a randomized control trial with 36 volunteers separated into three experimental groups:

  • Group 1 fasted on alternate days, with researchers asking them to eat 50 percent more than usual on eating days.
  • Group 2 reduced calories across all meals every day by 25 percent. This group represented more traditional dieting strategies.
  • Group 3 fasted on alternating days like group 1, but ate a full 100 percent more food than usual on eating days.

Ultimately, both groups 1 and 3 ended up losing less weight than participants in group 2. This held up even when calorie intake was virtually identical across groups.

“Many people believe that diets based on fasting are especially effective for weight loss or that these diets have particular metabolic health benefits even if you don’t lose weight,” says research leader Professor James Betts, director of Bath’s Centre for Nutrition, Exercise & Metabolism, in a university release. “But intermittent fasting is no magic bullet and the findings of our experiment suggest that there is nothing special about fasting when compared with more traditional, standard diets people might follow.”

Some fasting plans don’t seem to work at all

At the start of the experiment, all participants reported consuming a typical diet of around 2,000-2,500 calories per day on average. Then, over the three-week course of the study, groups 1 and 2 reduced their caloric intake down to 1,500-2,000 calories daily. The third group maintained the same energy levels by eating their usual amount of calories consumed in two days in the span of just one 24-hour period.

Moving on to weight loss, the traditional dieting group lost roughly 4.2 pounds over the three-week observation period. Moreover, body scans among this group showed nearly all the lost weight had been body fat content.

Meanwhile, group 1 lost nearly as much body weight (3.5 pounds), but only about half of that weight loss was due to reduced body fat. Researchers say the rest weight loss actually comes from lost muscle mass. Finally, group 3 barely lost any weight at all.

“Most significantly, if you are following a fasting diet it is worth thinking about whether prolonged fasting periods is actually making it harder to maintain muscle mass and physical activity levels, which are known to be very important factors for long-term health,” Prof. Betts concludes.

The study appears in the journal Science Translational Medicine.

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