Does fasting sixteen hours a day beat simply eating less? The most complete scientific answer to date is that, in practice, there’s barely any difference.
An international team published a network meta-analysis (a technique that lets researchers compare several strategies against each other, not just each one against a control group) in The BMJ, covering 99 randomized clinical trials and 6,582 adults. They compared the four most popular strategies: alternate day fasting, 16:8 time restricted eating, 5:2 fasting (eating normally 5 days and restricting heavily 2), and classic continuous calorie restriction.
All of them produce more weight loss than no change at all. That’s not surprising, eating less, whatever you call it, leads to weight loss. What’s interesting is the comparison between them: only alternate day fasting slightly outperforms simple continuous calorie restriction, by just 1.29 kilograms.
And that small edge has an expiration date: in trials lasting 24 weeks or longer, the difference disappears entirely. Long term, alternate day fasting and simply counting total daily calories end up producing practically identical results.
The authors searched PubMed, Embase, Cochrane Central and other clinical databases to locate randomized trials directly comparing these strategies, avoiding reliance on unreliable indirect comparisons between separate studies.
This considerably tempers the recent hype around intermittent fasting, especially against the rise of GLP-1 drugs as weight loss treatments: while those drugs achieve double digit percentage weight loss, intermittent fasting operates in the same modest territory as any other way of eating less, just a few kilos of difference compared to placebo or no intervention.
This doesn’t mean intermittent fasting is useless. For many people it’s easier to stick to day to day than constantly counting calories, and that practical adherence matters more long term than the theoretical metabolic superiority of one method over another. What the evidence does rule out is the idea that intermittent fasting has some magical metabolic effect independent of simply eating fewer total calories.
Source: Semnani-Azad Z, Khan TA, Chiavaroli L, et al. “Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials.” The BMJ, 2025. DOI: 10.1136/bmj-2024-082007.
