Intermittent Fasting: Cochrane Review Finds No Weight-Loss Advantage, Trial Shows Psychological Benefits

New research presents conflicting evidence on intermittent fasting for weight loss. A Cochrane review of 22 randomized clinical trials involving 1,995 adults found that intermittent fasting did not produce a clinically meaningful difference in weight loss compared with standard diet advice or no structured intervention. In contrast, an 18-month trial from Adelaide University found that intermittent fasting produced weight loss similar to continuous calorie restriction while appearing less psychologically burdensome.

The Cochrane review, published in the Cochrane Database of Systematic Reviews, examined trials conducted in North America, Europe, China, Australia, and South America. The studies tested alternate-day fasting, periodic fasting, and time-restricted feeding, with most following participants for up to one year. Compared with conventional diet advice or no intervention, fasting schedules did not outperform more traditional guidance or doing nothing specific. Researchers 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.

Few studies have examined how well intermittent fasting works over extended periods. The lead author of the review said intermittent fasting just doesn't seem to work for overweight or obese adults trying to lose weight, and 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." The authors emphasized that most trials included primarily white participants from high income countries, and because obesity is increasing rapidly in low and middle income nations, more research is needed in those populations. Findings may not apply equally to everyone; results could differ based on sex, age, ethnic background, medical conditions, or existing eating disorders. "Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight," said the senior author from Cochrane Evidence Synthesis Unit Iberoamerica.

Obesity remains a major public health concern and is 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 living with obesity.

A separate study offers a more nuanced view. The Adelaide University trial, published in Clinical Nutrition, enrolled more than 200 people with obesity and assigned them to one of three groups: intermittent fasting, continuous calorie restriction, or standard care. Participants in the intermittent fasting group ate 30% of their energy needs between 8 am and 12 pm on three nonconsecutive days each week, followed by a 20-hour fast; on non-fasting days they ate their usual diet. The calorie-restricted group ate 70% of their usual diet, while the standard care group received healthy eating guidelines.

After six months, people in both the intermittent fasting and calorie-restricted groups had lost about seven kilograms, compared with about two kilograms in the standard diet group. Participants also reported improvements in depression and wellbeing, including on fasting days. However, the psychological experience differed: those in the calorie-restriction group said they had to consciously focus on limiting how much they ate and avoiding overeating, and that increased sense of control explained 15% of their weight loss. Intermittent fasting participants did not feel they had to make major changes to their eating behaviors to lose weight.

A professor at Adelaide University's School of Medicine and the South Australian Health and Medical Research Institute said the results indicate intermittent fasting could offer an alternative pathway for people who find conventional dieting challenging. "Psychological and behavioral effects have a major influence on people's abilities to adhere to diets," she said. The researchers noted that although intermittent fasting has grown in popularity, its long-term psychological and behavioral effects are still not well understood compared with more traditional dieting methods. Future trials should be designed to identify individuals who struggle to improve eating behaviors, as they may do better with intermittent fasting diets, enabling more personalized weight management.