Intermittent fasting may make little difference to weight loss, large review finds
A comprehensive review of clinical trials has concluded that intermittent fasting is unlikely to deliver substantial short-term weight loss benefits for adults who are overweight or obese. While some physiological markers may improve, the analysis found little to no advantage over conventional dietary advice or receiving no advice at all.
What the review examined and what it found
The review pooled results from 22 randomised trials involving nearly 2, 000 adults monitored for up to 12 months. The trials evaluated common intermittent fasting approaches, including time-restricted eating—where food intake is limited to a daily window—and methods that alternate days of normal eating with days of very low calorie intake.
Across the trials, intermittent fasting produced minimal differences in weight loss when compared with standard dietary counselling focused on calorie reduction and healthier food choices. The same pattern emerged when fasting was compared with participants who received no guidance or were on waiting lists: there was little to no clear benefit for weight loss. Measures of quality of life also showed minimal change in most comparisons.
Lead review author Luis Garegnani said he was concerned by the level of enthusiasm for fasting online. "Intermittent fasting may be a reasonable option for some people, but the current evidence doesn't justify the enthusiasm we see on social media, " he said. Senior review author Eva Madrid added that clinical advice should be tailored: doctors need to take a case-by-case approach when recommending weight-loss strategies for overweight adults.
Limitations, uncertainty and unanswered questions
Reviewers expressed moderate confidence in the central finding that intermittent fasting offers little short-term weight-loss advantage. However, they flagged multiple limitations that weaken certainty about other potential effects. Many of the included trials were small and did not always use the most rigorous methods, which makes it difficult to isolate true treatment effects.
The review also highlighted gaps in the evidence. Trials used a variety of fasting schedules and intensities, and there was insufficient data to determine whether outcomes differ by sex, baseline BMI, or geographic and cultural settings. The impact of intermittent fasting on clinical measures beyond weight—such as blood glucose control in people with type 2 diabetes, blood lipids, and other markers of cardiometabolic health—remains unclear and requires larger, higher-quality studies.
Despite the limited weight-loss signal, reviewers noted some studies hint at improvements in certain biological functions with intermittent fasting. They cautioned, however, that these findings are preliminary and need confirmation in trials designed to test those specific outcomes rigidly.
What this means for people trying to lose weight
The headline takeaway for clinicians and people pursuing weight loss is pragmatic: intermittent fasting can be one of several tools available, but it should not be viewed as a magic solution. Individual response varies, and sustained weight loss typically depends on long-term dietary patterns, calorie balance, physical activity, and behavioural support.
Healthcare professionals should discuss options with patients, considering preferences, lifestyle, existing health conditions and the likelihood of maintaining any chosen eating pattern over months and years. For researchers, the verdict is clear—bigger, better-designed trials are needed to map who, if anyone, benefits most from intermittent fasting and which health measures it might reliably improve.
For now, intermittent fasting remains a plausible option for some, but the strongest available short-term evidence does not show a consistent advantage for weight loss over traditional dietary approaches or receiving no advice.
