healthHealth and Medicine

Intermittent Fasting No Better Than Calorie Restriction For Weight Loss, Finds Study


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

empty plate

but don't write it off just yet. Image: New Africa/Shutterstock

Somebody has probably at some point told you about a weight-loss technique called intermittent fasting. It comes in many forms, but the basic idea is to change not what you eat, but when you eat – and if certain Hollywood A-listers are to be believed, the effects are nothing short of miraculous.

Others, though, aren’t so convinced. And if the results of a newly published year-long trial are to be believed, the skeptics have it right.


“We found that the 8-hour time-restricted-eating regimen did not produce greater weight loss than the regimen of daily calorie restriction, with both regimens resulting in similar caloric deficits,” reports the paper, published this week in the New England Journal of Medicine.

“In addition, time-restricted eating and daily calorie restriction produced similar effects with respect to reductions in body fat, visceral fat, blood pressure, glucose levels, and lipid levels over the 12-month intervention period,” the authors add.

Intermittent fasting as a method of controlling obesity is fairly controversial in the scientific world, with the majority of evidence being what researchers call “low-quality.”

This new study, though, has a few key advantages: the trial “included a culturally sensitive, prescription-based intervention, similar caloric restriction and attention to dietary quality in the two groups,” the authors explain, as well as benefitting from a relatively long duration and low drop-out rate among the participants.


That’s pretty impressive because the study had some rather stringent rules. The participants – 71 men and 68 women – were required to reduce their daily caloric intake to just 1,500 to 1,800 kcal for men and 1,200 to 1,500 kcal for women, which was about three-quarters of the average baseline intake. This was to take the form of 40 to 55 percent carbohydrates, 15 to 20 percent protein, and 20 to 30 percent fat – participants were encouraged to weigh their food to make sure they were consuming the right proportions.

They received dietary counseling from trained health coaches, and dietary information booklets with portion advice and sample menus to follow. More than that, they were told to record their food intake scrupulously, using a written food log, photographs, and a custom mobile app.

For half the participants, this wasn’t the end of the restrictions. The group who found themselves randomly assigned to the intervention group were only allowed to take in those calories for eight hours a day – between 8 a.m. and 4 p.m. If the key to weight loss really did lie in timing your meals, then that should have given the fasting group an edge that the non-fasting group simply didn’t have.

But after a year of all this hard work, the results were in: the two diets performed almost completely the same.


“In our trial, we found that the two weight-loss regimens that we evaluated had similar success in patients with obesity, regardless of whether they reduced their calorie consumption through time-restricted eating or through calorie restriction alone,” the researchers concluded.

Both groups lost weight – the fasting group lost eight kilograms from baseline (about 17 pounds), while the non-fasters lost 6.3 kilograms (about 14 pounds). That’s not a statistically significant difference, but it does mean one thing: intermittent fasting may not be better than normal calorie restriction, but it isn’t any worse, either.

It’s worth mentioning, too, that dieters in the world outside of clinical trials rarely have the time or resources to hire full-time dietary coaches and a team of interested researchers to follow their progress and adherence – and, as doctors Blandine Laferrère and Satchidananda Panda point out in an editorial accompanying the study, this trial took place in China, where all-day snacking isn’t so much of a thing as it is in Western countries like the US.

In other words, it may not be the silver bullet that turns a normal diet into a miracle cure, but that doesn’t mean intermittent fasting isn’t still the best route for some slimmers.


“The concept of time-restricted eating is evolving,” write Laferrère and Panda. “Future studies will determine the appropriate duration of the time window for eating, who is most likely to benefit from this approach, how to implement time-restricted eating and the potential mechanisms for doing so, and the effects of time-restricted eating early in the day as compared with late in the day.”

“From a public health point of view, time-restricted eating may turn out to be an approach to accomplish calorie restriction and improve metabolic health without the resource-intensive approach of intentional calorie restriction.”


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