Intermittent fasting fails to beat standard dieting for weight loss

Obesity remains a major public health concern and is now one of the leading causes of death in high income countries. The World Health Organization reports that adult obesity rates have more than tripled globally since 1975. In 2022, about 2.5 billion adults were overweight, including 890 million who were living with obesity.

At the same time, intermittent fasting has gained enormous popularity. Social media trends, wellness influencers, and claims of fast weight loss and improved metabolism have helped turn fasting into a mainstream strategy.

Review of 22 Clinical Trials Finds No Clear Benefit

To evaluate whether intermittent fasting truly offers an advantage, researchers examined data from 22 randomized clinical trials involving 1,995 adults in North America, Europe, China, Australia, and South America. The studies tested different fasting methods, including alternate-day fasting, periodic fasting, and time-restricted feeding. Most followed participants for up to one year.

When compared with conventional diet advice or no intervention, intermittent fasting did not produce a clinically meaningful difference in weight loss. In practical terms, fasting schedules did not outperform more traditional guidance or doing nothing specific.

Researchers also noted that side effects were not consistently reported across studies, making it difficult to fully assess potential risks. With only 22 trials available, many of them small and uneven in their reporting, the overall evidence base remains limited.

"Intermittent fasting just doesn't seem to work for overweight or obese adults trying to lose weight," said Luis Garegnani, lead author of the review from the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre.

Social Media Hype vs Scientific Evidence

Garegnani cautioned that online enthusiasm may be running ahead of the data. "Intermittent fasting may be a reasonable option for some people, but the current evidence doesn't justify the enthusiasm we see on social media."

Another concern is the lack of long term research. Few studies have examined how well intermittent fasting works over extended periods. "Obesity is a chronic condition. Short-term trials make it difficult to guide long-term decision-making for patients and clinicians," Garegnani added.

Most of the trials included primarily white participants from high income countries. Because obesity is increasing rapidly in low and middle income nations, more research is needed in these populations.

The authors emphasize that the findings may not apply equally to everyone. Results could differ based on sex, age, ethnic background, medical conditions, or existing eating disorders or behaviors.

"With the current evidence available, it's hard to make a general recommendation," said Eva Madrid, senior author from Cochrane Evidence Synthesis Unit Iberoamerica. "Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight."