Researchers leading a Cochrane-style review published on 16 February 2026 report that intermittent fasting yields no clear advantage over standard dietary advice for people with overweight or obesity. The analysis pooled randomized trials from 22 studies involving 1,995 adults across Europe, North America, China, Australia and South America and found average weight loss from fasting approaches was roughly 3% of body weight. That figure falls short of the 5% reduction clinicians usually treat as the threshold for a clinically meaningful effect, and most trials lasted no longer than 12 months. The authors conclude intermittent fasting may be an option among several but is not a superior strategy for weight loss based on current evidence.
Key takeaways
- The review synthesised 22 randomized trials with 1,995 adult participants from five world regions, using Cochrane-level methods to appraise the evidence.
- Average body-weight reduction with intermittent fasting across trials was about 3%, below the 5% benchmark considered clinically meaningful by many clinicians.
- Intermittent fasting formats studied included alternate-day fasting, the 5:2 regimen (two fast days per week) and time-restricted eating; results were broadly similar across types.
- Most trials were short term, with follow-up periods up to 12 months; long-term outcomes remain largely untested.
- There was no consistent evidence that intermittent fasting produced larger improvements in quality of life compared with conventional diets.
- Study quality and reporting were variable; notably, none of the included trials reported participant satisfaction with fasting regimens.
- Experts note behavioural factors—lower activity during fasting, poor adherence and heterogeneous fasting definitions—may blunt measurable benefits.
Background
Intermittent fasting (IF) has become a mainstream dieting approach in the past decade, promoted for weight control and claimed to improve metabolic health and longevity. Popular formats range from daily time-restricted eating windows to plans that prescribe whole-day or alternate-day calorie restriction; the 5:2 diet, made widely known by Michael Mosley, remains one of the better-known variants. Researchers and clinicians have debated whether the reported metabolic effects—improved insulin sensitivity, altered fat metabolism and activation of autophagy—translate into measurable clinical gains for people who are overweight or have obesity.
Prior trials and meta-analyses have given mixed signals, in part because IF lacks a single, standard definition and studies differ in duration, participant characteristics and outcome measures. Public interest and commercial promotion of fasting approaches have outpaced the accumulation of long-term, high-quality randomized evidence. Against this backdrop, systematic reviews that apply rigorous inclusion criteria and standardised analysis are designed to clarify whether IF offers advantages beyond conventional calorie-reduction strategies.
Main event
The new review applied established Cochrane methods to randomized controlled trials comparing intermittent fasting to conventional dietary advice or no specific diet. The team identified 22 eligible trials enrolling 1,995 adults from diverse settings; follow-up durations were up to 12 months. Across trial types and populations, average weight loss with intermittent fasting was approximately 3% of baseline body weight—statistically detectable but below the 5% threshold many clinicians regard as clinically meaningful for cardiometabolic benefit.
Beyond weight, the review did not find robust evidence that fasting regimens improved quality of life more than standard diets. The authors highlighted limitations: many trials were small, some had methodological weaknesses, and adherence and satisfaction were poorly measured. Lead author Dr Luis Garegnani, director of the Cochrane Associate Centre at the Italian hospital of Buenos Aires, emphasised that intermittent fasting appears to perform similarly to traditional approaches rather than outperforming them.
Commentators noted biological mechanisms that motivate fasting research—circadian timing, insulin sensitivity, inflammation and autophagy—are mainly established in animal studies or under tightly controlled conditions. Several experts pointed out that brief fasting periods in free-living humans may not elicit the same metabolic shifts, and that behavioural responses such as reduced physical activity or compensatory eating can offset calorie deficits during fasting intervals.
Analysis & implications
Clinicians should interpret the evidence as indicating intermittent fasting is a viable but not superior option for weight management compared with standard dietary counselling. For individual patients, choice of approach should consider preferences, comorbidities, medication schedules (for example diabetes drugs), and the likelihood of sustained adherence rather than assuming IF will deliver larger weight loss. The modest average effect size in the review suggests population-level benefits from IF alone are likely limited unless adherence improves or the approach is combined with other evidence-based treatments.
From a research and policy perspective, the review exposes important gaps: most trials are short, inconsistent in how fasting is defined and rarely include patient-centred endpoints such as satisfaction, daytime function or long-term cardiometabolic events. Regulators and guideline developers should avoid claims that IF is categorically superior; messaging ought to emphasise that a range of dietary approaches can produce modest weight loss when followed consistently.
The biological questions remain open. Some investigators argue that longer or more extreme fasting protocols may trigger deeper metabolic remodelling—changes to proteins, autophagy or inflammatory pathways—that short trials do not capture. But longer or more restrictive regimens raise feasibility and safety concerns, and benefit in humans has not been established in randomized trials with clinically relevant endpoints.
Comparison & data
| Metric | Value / finding |
|---|---|
| Trials included | 22 randomized trials |
| Participants | 1,995 adults |
| Average weight loss with IF | ~3% body weight |
| Clinically meaningful threshold | 5% body weight |
| Follow-up | Up to 12 months (short term) |
The table summarizes the core quantitative findings underpinning the review. The modest gap between observed IF weight loss (~3%) and the 5% clinical threshold underlines why reviewers judged benefits limited. Heterogeneity in trial design and short follow-up times mean these averages mask variability across protocols and participant groups; longer, well-powered studies would be needed to detect smaller but clinically relevant subgroup effects.
Reactions & quotes
Review lead Dr Luis Garegnani framed the results as clarification rather than condemnation: he told the authors and media that intermittent fasting is not a miracle but can be one of several tools for weight management. He urged caution in overpromoting fasting claims until higher-quality, longer trials address unresolved questions such as adherence and patient preference.
“Intermittent fasting likely yields results similar to traditional dietary approaches; it does not appear clearly better, but it is not worse either.”
Dr Luis Garegnani, Cochrane Associate Centre (lead author)
Dr Zhila Semnani-Azad of the National University of Singapore highlighted circadian biology as a plausible modifier of outcomes, noting that meal timing interacts with metabolic regulation. She acknowledged animal data supporting timed fasting effects on insulin sensitivity and inflammation but stressed human trial evidence on timing and clinical endpoints is inadequate.
“Timing matters: circadian rhythms shape metabolism, and this could influence effects, but robust human trials are lacking.”
Dr Zhila Semnani-Azad, National University of Singapore
Professor Maik Pietzner from the Berlin Institute of Health noted that short fasting windows often produce small changes in biomarkers, and that more prolonged fasting was required in his work to provoke larger shifts. He also pointed to behavioural factors—reduced activity and low adherence—that can erode potential benefits in free-living participants.
“Brief fasts have limited physiological impact for most people; meaningful changes may need longer fasting but that raises feasibility issues.”
Prof Maik Pietzner, Berlin Institute of Health
Unconfirmed
- Long-term impacts of intermittent fasting on weight maintenance and cardiometabolic events beyond 12 months remain unproven.
- The degree to which circadian timing of eating delivers clinically meaningful benefits in humans is not yet confirmed.
- Claims that fasting improves cognitive function, slows aging or reliably triggers beneficial autophagy in humans are not established by the trials included in the review.
- Participant satisfaction and real-world adherence to fasting regimens were not assessed across the 22 trials and thus remain uncertain.
Bottom line
The Cochrane-style review provides the clearest randomized-evidence summary to date: intermittent fasting produces modest weight loss—around 3% on average—and does not outperform conventional dietary advice in the short-term trials analysed. For clinicians and people seeking weight loss, IF can be offered as one option among several, but it should not be presented as a superior solution given current data.
Future research should prioritise longer follow-up, standardized definitions of fasting protocols, attention to patient-centred outcomes (satisfaction, daily function) and trials that examine clinically meaningful endpoints. Until then, messaging should emphasise realistic expectations: modest average benefits, variable individual responses, and the importance of sustained adherence and comprehensive care for meaningful long-term outcomes.
Sources
- The Guardian — media report summarising the Cochrane-style review and expert reactions.
- Cochrane Library — systematic review repository and methodology reference (official systematic review resource).