Major review finds intermittent fasting offers little extra weight loss benefit
A large new systematic review of clinical trials concludes that intermittent fasting is unlikely to produce meaningful additional weight loss for adults living with overweight or obesity when compared with standard dietary advice or no advice. The analysis pooled results from 22 trials involving nearly 2, 000 participants and found only small average changes in body weight over periods up to 12 months.
What the review examined and what it found
Researchers looked at randomized trials testing a range of intermittent fasting approaches — including time-restricted eating (daily eating windows), alternate-day fasting and the two-day-a-week method — against traditional calorie-reduction guidance or waiting-list controls. Across the studies, average weight loss from fasting-based plans was modest: roughly 3% of body weight, under the 5% threshold clinicians typically regard as a clinically meaningful improvement.
When compared with conventional dietary advice such as calorie reduction and healthier food choices, intermittent fasting made little to no difference for weight loss or for measures of quality of life. The same minimal effects appeared when fasting approaches were compared with no formal advice, though the evidence on life-quality impacts was less clear.
Potential benefits beyond pounds lost — and important limits
Although the weight-loss signal was small, some researchers highlight possible metabolic benefits that warrant further study. Trial and laboratory evidence suggests fasting can affect insulin sensitivity, inflammation and how the body mobilizes fat, and it may trigger cellular processes such as autophagy that are linked with longer-term health effects. Timing of eating in relation to the body’s circadian rhythm is another area of interest that could influence results.
Lead review author Luis Garegnani warned that online enthusiasm for fasting has outpaced the evidence: "Intermittent fasting may be a reasonable option for some people, but the current evidence doesn't justify the enthusiasm we see on social media. " Senior author Eva Madrid emphasized a personalised approach, noting that clinicians will need to assess individual circumstances when advising on weight-loss strategies.
At the same time, the review authors expressed only moderate confidence in the overall findings and highlighted key limitations. Many included trials were small, of short duration (no longer than 12 months), and varied widely in design and adherence measurement. That heterogeneity makes it hard to draw firm conclusions about subgroups such as men versus women, different BMI ranges, or people with underlying conditions like type 2 diabetes.
What this means for people trying to lose weight
For adults seeking weight loss, the review suggests intermittent fasting is neither a clear superior strategy nor a guaranteed shortcut. It appears to yield outcomes similar to traditional calorie-reduction plans for many people, and may be an acceptable option for those who prefer its structure. Practical factors — including personal preference, lifestyle fit and the ability to sustain an eating plan — remain crucial determinants of long-term success.
Some experts caution that fasting can lead to reduced activity levels for certain individuals, which could blunt weight-loss efforts. The overall message for clinicians and the public is that intermittent fasting is one tool among several. More large, well-designed trials are needed to clarify long-term effects, metabolic benefits, and whether specific timing patterns or subgroups might gain greater advantage.
