A new review has found that intermittent fasting does not produce significantly greater weight loss in overweight or obese adults compared to traditional dietary advice or doing nothing. The findings challenge claims that fasting regimes, popularized on social media, lead to rapid or superior results.
Obesity has become a leading public health issue worldwide. According to the World Health Organization, adult obesity has more than tripled since 1975. In 2022, an estimated 2.5 billion adults were classified as overweight, including 890 million living with obesity. Rising awareness of these trends has contributed to the popularity of intermittent fasting, in which people go for extended periods without eating. Popular methods include the 16:8 plan—16 hours of fasting with an eight-hour eating window—and 24-hour fasts twice per week.
Researchers conducting the review analysed data from 22 randomised clinical trials involving 1,995 adults across North America, Europe, China, Australia, and South America. The studies examined various forms of intermittent fasting, including alternate-day fasting, periodic fasting, and time-restricted feeding, with most following participants for up to 12 months.
The review, published in the Cochrane Library, compared fasting with standard dietary advice, such as the Mediterranean diet, and with no intervention. On average, people who practised intermittent fasting lost about 3 percent of their body weight, below the 5 percent threshold doctors often consider necessary to achieve meaningful health benefits. The results showed no clear advantage over traditional diets or maintaining usual eating habits.
Luis Garegnani, lead author of the review from the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre, said, “Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight.” He cautioned against the hype surrounding fasting on social media, noting that it may be a reasonable option for some individuals but lacks strong evidence of superiority.
The review also highlighted gaps in the research. Side effects were inconsistently reported across trials, and most studies involved predominantly white populations in high-income countries. The authors stressed the need for research in low and middle-income countries, where obesity is rising rapidly, and warned that results may vary depending on factors such as age, sex, ethnic background, and underlying health conditions.
Eva Madrid, senior author from the Cochrane Evidence Synthesis Unit Iberoamerica, noted, “With the current evidence available, it’s hard to make a general recommendation. Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight.”
The study underscores that, while intermittent fasting remains popular, its benefits for weight loss may be modest. Experts suggest focusing on sustainable dietary and lifestyle changes rather than expecting dramatic results from fasting alone.
