A major Cochrane review challenges popular claims about intermittent fasting, suggesting it may help with weight loss but offers no meaningful advantage over conventional calorie restriction.
Review: Intermittent fasting for adults with overweight or obesity. Image Credit: Tetiana Chernykova / Shutterstock
In a recent systematic review published in the Cochrane Database of Systematic Reviews, researchers synthesized data from 22 randomized controlled trials involving 1,995 participants to evaluate the efficacy of intermittent fasting (IF) for adults with overweight or obesity. The review compared various fasting regimens against regular dietary advice, such as continuous calorie restriction, and no intervention.
Review findings suggest that, contrary to popular belief, IF results in little to no difference in weight loss compared to traditional dieting methodologies, based largely on low- to very-low-certainty evidence with potential risk of bias. While the evidence regarding IF’s impact on participants’ quality of life (QoL) and adverse side effects remains uncertain, the review concludes that IF is a potentially viable but not superior weight-loss strategy based on generally low-certainty evidence. Any statistically observed differences were generally considered unlikely to translate into clinically meaningful advantages.
Obesity is frequently highlighted as one of the most severe behaviorally modifiable public health challenges and is predicted to substantially worsen in the coming years. Clinically defined as a body mass index (BMI) exceeding 30 kg/m2, obesity has traditionally been treated with continuous energy restriction, a reduction in daily caloric intake.
A growing body of research highlights that adherence to energy restriction regimens is difficult, often leading to a "yo-yo" effect in which weight that may be temporarily lost is subsequently regained. These challenges have contributed to the popularity of several fasting programs, many of which are marketed as metabolic "biohacks" that purportedly promote and sustain weight loss.
Intermittent fasting (IF) is one of the most popular approaches, characterized by alternating periods of normal caloric intake with extended periods of little to no food consumption. Proponents posit that fasting triggers physiological benefits beyond simple calorie reduction, such as improved insulin sensitivity and increased fat metabolism. However, these claims remain incompletely substantiated in human clinical evidence, and current data are insufficient to confirm clinically meaningful metabolic advantages beyond calorie restriction alone.
Systematic Review Methods and Comparisons
The present systematic Cochrane review evaluated the potential benefits and drawbacks of IF regimens. Data were collated from several major scientific publication repositories, including CENTRAL and MEDLINE (Ovid), and comprised randomized controlled trials (RCTs) investigating IF in adults aged 18 years or older who were overweight or obese.
The combination of a custom search strategy and screening of titles, abstracts, and full texts yielded 22 RCTs comprising 1,995 participants. Analyses investigated three primary comparisons.
IF versus regular dietary advice (RDA): This comparison evaluated IF protocols, such as time-restricted feeding or alternate-day fasting, against conventional continuous energy restriction or dietary counseling.
IF versus no intervention: This comparison evaluated patients on IF regimens against those on waiting lists or receiving no treatment despite being overweight or obese.
Impacts of IF on safety and participant experience: Included publications were analyzed for adverse events and QoL outcomes.
The primary outcome was the percentage change in body weight from baseline. Secondary outcomes included the proportion of participants achieving at least 5% weight reduction, a validated clinical benchmark for health improvement, planned metabolic outcomes such as lipid profiles, and participant-reported QoL changes. Several planned outcomes, including participant satisfaction and diabetes status, were not reported in the included trials. Evidence certainty was generally low for comparisons involving dietary advice and moderate for some comparisons without intervention.
Weight Loss Outcomes and Clinical Benchmarks
When comparing IF to RDA, analysis of 21 studies involving 1,430 participants showed a mean difference (MD) in weight loss of -0.33% (95% confidence interval (CI) -0.92 to 0.26), indicating similar weight loss across intervention approaches. Evidence certainty was rated low.
The clinical benchmark of achieving at least 5% body weight reduction yielded a risk ratio (RR) of 0.98 (95% CI 0.82 to 1.18), suggesting that IF did not increase the likelihood of clinically significant weight loss compared with conventional RDA approaches. Confidence in this estimate was rated very low.
When comparing IF to no intervention, fasting participants showed greater weight reduction, with MD = -3.42% (95% CI -4.95 to -1.90). Although evidence certainty for this comparison was moderate, the authors interpreted the difference as unlikely to be clearly clinically meaningful, and long-term sustainability remains uncertain. Most studies assessed outcomes over 6 to 12 months, limiting conclusions regarding long-term effects.
QoL data were sparse, reported in only three included trials, and suggested that IF did not significantly improve mental or physical QoL compared with standard diets.
Some studies reported adverse events, including headaches, nausea, and fatigue. However, findings were inconsistent and imprecise, preventing firm conclusions about whether IF carries higher risks than standard dieting. Overall evidence certainty for safety outcomes was low or very low.
Clinical Interpretation and Evidence Limitations
This review establishes IF as an alternative dietary approach that appears broadly comparable to, but not superior to, traditional calorie-restriction methods or standard diets. Healthcare providers and the general public may consider IF based on personal preference, practicality, and sustainability rather than expectations of superior weight-loss outcomes. Interpretation should remain cautious given the limited trial duration, methodological variability, and overall low certainty of evidence. Longer-term, higher-quality trials are needed before firm clinical recommendations can be made.
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