Intermittent fasting produces little to no difference in weight loss compared with regular dietary advice for adults with overweight or obesity, according to a Cochrane systematic review of 22 randomized controlled trials encompassing 1995 participants.
The review examined trials conducted in outpatient settings across North America, Australia, China, Denmark, Germany, Norway, and Brazil between 2016 and 2024. Investigators pooled data from studies evaluating time-restricted feeding, periodic fasting, alternate-day fasting, and modified alternate-day fasting regimens lasting at least 4 weeks.
When compared with regular dietary advice—typically calorie restriction or structured eating plans—intermittent fasting resulted in a mean difference of −0.33% from baseline body weight across 21 studies with 1430 participants. The certainty of this evidence was rated low due to concerns about risk of bias. For the categorical outcome of achieving 5% body weight reduction, four studies with 472 participants showed near-equivalent rates between groups, though evidence certainty was very low.
Quality-of-life, assessed using validated instruments including the Assessment of Quality of Life-8D, SF-36, and RAND-36 surveys, showed little to no difference between intermittent fasting and conventional dietary approaches across three studies with 106 participants.
Against no intervention or waiting list controls, intermittent fasting demonstrated a mean difference of −3.42% weight loss from baseline across six studies with 427 participants. The review authors characterized this as moderate-certainty evidence that intermittent fasting likely results in little to no difference in weight loss compared with no intervention, suggesting the effect may not be clinically meaningful.
Intermittent fasting may result in little to no difference in adverse events compared with regular dietary advice, though the evidence was very uncertain. Seven studies comparing the approaches showed substantial heterogeneity (I² = 78%), limiting interpretation. Reported adverse events included nausea, headache, dizziness, hunger, constipation, diarrhea, dyspepsia, cold intolerance, irritability, insomnia, and impaired concentration.
Subgroup analyses suggested potentially higher adverse event rates with modified alternate-day fasting and alternate-day fasting compared with time-restricted feeding. Studies conducted in high-income countries showed increased adverse events with intermittent fasting, while the single study from a low- or middle-income country suggested reduced events; however, the review authors noted these findings are limited by small numbers of studies per subgroup.
The review identified several evidence gaps. No included studies reported participant satisfaction, diabetes status, or overall measures of comorbidity. Nineteen of 22 studies were conducted in high-income countries, with none from low-income settings. Seven studies were exclusive or predominantly (>80%) women, and one study was exclusive or predominantly men, limiting sex-specific conclusions. Most included studies focused on short-term outcomes up to 12 months.
"Physicians and patients may need to evaluate willingness and readiness to implement intermittent fasting as a treatment strategy, based on individual practicality and sustainability," the authors wrote.
The review reported no dedicated funding. Eight included studies disclosed conflicts of interest related to grants, employment, or advisory relationships with private companies.
