intermittent fasting weight loss review finds minimal benefit for most overweight adults
A large analysis of randomised trials finds that popular intermittent fasting approaches — including the 5: 2 model and time-restricted eating — produce little to no additional weight loss or improvement in quality of life for adults who are overweight or living with obesity. The team behind the review says intermittent fasting may still influence biological markers of health, but current evidence is limited and short term.
What the review examined and what it found
Researchers pooled data from 22 clinical trials involving about 1, 995 adults across multiple regions to compare short-term intermittent fasting (up to 12 months) with conventional dietary advice or no advice. The fasting strategies studied ranged from alternate-day fasting to weekly calorie-restriction plans and restricted daily eating windows.
On measures of weight loss and self-reported quality of life, intermittent fasting made little to no difference compared with standard dietary guidance such as calorie reduction and healthier food choices. When set against no intervention or delayed advice, fasting produced only marginal extra weight loss, with average reductions around 3% of body weight — below the 5% threshold clinicians often view as clinically meaningful.
Lead review author Luis Garegnani called the contrast between online enthusiasm and the evidence a concern, noting that intermittent fasting may be a reasonable choice for some individuals but does not appear to outperform traditional approaches overall. Senior author Eva Madrid urged tailored clinical discussions, stressing that physicians should evaluate patients case by case.
Limitations of the evidence and unanswered questions
The researchers graded their confidence in the main weight-loss findings as moderate, but flagged serious limitations across the body of evidence. Many trials were small, used less robust methods, and ran for relatively short periods, restricting the ability to detect lasting effects or harms. Trials also varied widely in how fasting was defined and implemented, complicating direct comparison.
Key gaps remain. Few studies separated outcomes by sex, baseline BMI category or geographic region, and none systematically measured whether people were satisfied with fasting regimens over time. The review team highlighted uncertainty around the long-term impact of intermittent fasting on conditions such as type 2 diabetes, cardiovascular risk markers and markers of inflammation and metabolism.
Laboratory and animal research hints at physiological mechanisms — shifts in how the body uses fat, improved insulin sensitivity, reductions in inflammation and activation of cellular recycling processes — that could deliver health benefits independent of weight loss. But translating those signals into reliable clinical effects for people will require larger, longer and better-controlled trials.
Practical takeaways for people trying to lose weight
For now, intermittent fasting should be viewed as one option among several rather than a miracle solution. It may suit some individuals’ lifestyles and preferences, and for those people adherence is often the most important factor for success. Clinicians should weigh fasting against other evidence-based strategies and consider patient preferences, medical history and potential risks.
The review underscores a broader truth about dieting: sustainable change frequently depends more on long-term habits and support than on a single named approach. The current evidence base does not justify the level of hype fasting sometimes receives online, but it leaves the door open for future research to clarify whether certain fasting schedules or subgroups of people could derive distinct benefits.
