Intermittent fasting may make little difference to weight loss, review finds

A comprehensive review of short-term trials suggests popular intermittent fasting approaches — including time-restricted eating and alternate-day restriction — produce little to no advantage for weight loss or quality of life compared with conventional dieting advice or no guidance. The review evaluated 22 trials on almost 2, 000 adults, with interventions lasting up to 12 months.

What the review found

Researchers pooled results from 22 randomized trials to assess if intermittent fasting helped adults with overweight or obesity lose more weight than standard dietary advice or no intervention. On average, the differences in weight loss were small and often clinically negligible. Quality-of-life measures showed similarly modest or unclear effects.

Intermittent fasting in the examined trials took several forms. Some studies focused on daily time-restricted eating, commonly an eating window of about eight hours, while others used alternate-day or periodic restriction such as the 5: 2-style pattern. Across these varied approaches, the review’s overall conclusion was consistent: intermittent fasting was not clearly superior to traditional calorie-reduction advice or to being placed on a waiting list for help.

That said, the review team did flag that intermittent fasting might still produce beneficial shifts in some physiological markers tied to metabolic health. These potential improvements were not robustly established across studies, and the authors called for more targeted research to determine whether fasting patterns can meaningfully affect outcomes such as blood sugar control or cardiovascular risk factors.

Limits, uncertainties and the evidence base

Authors of the review expressed cautious confidence in the main findings but emphasised important limitations. Many trials were small, short in duration or used methods that make it difficult to draw firm, long-term conclusions. Follow-up in most studies extended only up to 12 months, and trial populations, intervention details and outcome measures varied substantially, introducing heterogeneity into pooled estimates.

Geographic diversity was wide — trials were conducted across Europe, North America, China, Australia and South America — yet data were insufficient to robustly compare effects by sex, baseline body-mass index or other key subgroups. The review also noted the multiple forms of intermittent fasting used in practice; without standardized protocols it is hard to generalise findings from a mix of trial designs to any single fasting regimen.

Given these constraints, the authors called for larger, better-conducted trials with longer follow-up and clearer reporting on secondary outcomes such as diabetes control and other health conditions. They also highlighted the need to examine how different fasting patterns affect men and women differently and how cultural or dietary contexts might change results.

Practical takeaways for clinicians and the public

Lead reviewers urged clinicians to weigh intermittent fasting as one tool among many rather than a one-size-fits-all solution. Some people may find time-restricted eating or alternate-day plans easier to follow, and those individuals might sustain adherence better than with standard calorie-counting approaches. For others, traditional dietary advice focused on balanced intake and portion control may be equally or more effective.

Experts emphasised a case-by-case approach when advising patients with overweight or obesity. Intermittent fasting could be a reasonable option for motivated individuals without contraindications, but the hype around fasting should be tempered by the current evidence. Until more rigorous long-term data are available, intermittent fasting should not be considered a guaranteed shortcut for weight loss or a substitute for individualized medical guidance.

In short, intermittent fasting remains a viable choice for some, but the evidence does not currently support strong claims that it consistently outperforms standard dieting approaches for weight loss or quality of life.