Health and Medicine
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Intermittent fasting – periods of eating little or nothing interspersed with normal food consumption – isn't an effective way to lose weight, according to a review of 22 randomized controlled trials. It seems that assurances from celebrity weight-loss gurus and appeals to historical precedent aren’t enough make a practice work.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Religions have encouraged or directed their adherents to refrain from eating, and in some cases even drinking water, to mark holy days or show penitence for thousands of years. In recent times, social media has been filled with those who advocate engaging in fasts for weight loss instead. The fact the practice has been so widespread for so long has been touted as evidence of its effectiveness. Until recently, however, most fasts were conducted in a world where calories were harder to come by the rest of the time, and whatever people's reasons for fasting, shedding fat wasn't high among them.
Nevertheless, there have been some scientific studies that report benefits from intermittent fasting, at least in the short term, and these have received considerable prominence in the media. However, a Cochrane Review – an assessment of the best peer-reviewed research available – has found the overall picture looks very different.
The review drew on 22 trials involving a total of 1,995 people lasting between 2 and 12 months, with most at the longer end of that range. Diets that help people lose weight initially, but are no good for keeping it off, are two-a-penny, so a more extended timeframe was essential. “Obesity is a chronic condition. Short-term trials make it difficult to guide long-term decision-making for patients and clinicians,” said Dr Luis Garegnani at the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre in a statement.
The trials divided participants randomly into those directed to fast and those who were either given traditional advice about a balanced diet, or were left to their own devices.
Every trial was different, so the review's authors found there were some questions they couldn't answer. For example, only some of the studies reported on side-effects, and they couldn't draw confident conclusions from those that did. Complicating matters further, some studies included anyone who was looking to lose weight through intermittent fasting, while others were restricted to those with specific conditions, such as non-alcoholic fatty liver disease.
However, side-effects are only really important to discuss in the context of a treatment that actually works, and that is doubtful at best. “Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” Garegnani concluded. The one study that looked at quality of life found no benefit from the fasting regime, although the sample size here was so small that this isn't surprising.
Considered individually, none of the 22 studies showed a statistically significant difference between intermittent fasting and regular advice. A few got close, but in some of those the regular advice performed better.
There are several caveats to the review's conclusion. The first is that most of the studies were conducted in wealthy and predominantly white countries, so the results may not be applicable worldwide. However, since these are the places where intermittent fasting has proven most popular in recent times, that may not matter much.
Eight of the studies only included women participants, whereas only one study was exclusively men. This creates an overall skew, but there’s no evidence that changed the result.
Some of the benefits attributed to intermittent fasting, such as diabetes control, weren't investigated in any of the studies, and only 10 of the trials reported on how well people stuck to their fasting regimes.
Perhaps most importantly, the trials used a variety of different fasting regimes. Some had people fast between certain hours every day, others involved one or two days a week without eating, while still others had people restrict what they ate every second day.
The consequence is that, while the overall sample is substantial, the numbers for specific fasting regimes are sometimes small. Consequently, it is possible that there is an effective way to fast, but the numbers involved in the relevant trials were insufficient to show that. Based on the data collected, however, that doesn’t appear to be a likely outcome.
The study is published in Cochrane Database of Systematic Reviews.
