A new study found that weight loss from fasting was barely greater than doing nothing, and similar to results from traditional dietary advice.
Intermittent fasting is unlikely to lead to greater weight loss in overweight or obese adults than traditional dietary advice, a new review has found. Obesity is a significant public health problem and has become a leading cause of death in high-income countries. Worldwide adult obesity has more than tripled since 1975, according to the World Health Organization (WHO).
In 2022, 2.5 billion adults were classified as overweight, including 890 million living with obesity.
Intermittent fasting, where you go for extended periods of time without eating, has surged in popularity in recent years – fuelled by social media, lifestyle influencers and claims of rapid weight loss.
One popular approach involves fasting for 16 hours and having an 8-hour eating window. Some people swear by 24-hour fasts twice per week.
However, the latest evidence suggests the benefits of these methods may be limited. Researchers analysed evidence from 22 randomised clinical trials involving 1,995 adults across North America, Europe, China, Australia, and South America. The studies assessed multiple forms of intermittent fasting, including alternate-day fasting, periodic fasting, and time-restricted feeding. Most followed participants for up to 12 months.
The review, published in the Cochrane Library, compared intermittent fasting with traditional dietary advice (such as the Mediterranean diet) and with no intervention. Intermittent fasting did not appear to have a clinically meaningful effect on weight loss compared to standard dietary advice or doing nothing.
On average, people who followed intermittent fasting lost around 3 percent of their body weight – below the 5 percent threshold that doctors often consider clinically meaningful for improving health outcomes. Reporting of side effects was inconsistent across trials, making it difficult to draw firm conclusions. The evidence base remains limited, with only 22 trials, many with small sample sizes and inconsistent reporting.
“Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” said Luis Garegnani, the lead author of the review from the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre.
Garegnani also cautioned against the hype surrounding 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.”
Few trials have examined the long-term results of intermittent fasting. “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 included studies involved predominantly white populations in high-income countries. As obesity is a rapidly growing crisis in low and middle-income countries, further research is needed in these populations.
The authors warned that the findings may provide clues, but cannot be applied to the entire population, as results may vary depending on sex, age, ethnic origin, disease status or underlying eating disorders. “With the current evidence available, it’s hard to make a general recommendation,” said Eva Madrid, a 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.” (Euro News)
