A major review of scientific evidence has found intermittent fasting offers no superior weight loss benefits compared to conventional diets, and is barely more effective than not dieting at all. The analysis of 22 global studies, published by Cochrane, revealed individuals who were overweight or obese lost roughly the same amount of weight following traditional dietary advice as those who tried fasting regimes like the 5:2 diet, popularized by the late Dr. Michael Mosley.
Researchers found that, on average, people lost only around 3% of their body weight through intermittent fasting – a figure considered far below the 5% threshold that doctors generally view as clinically meaningful. The studies included in the review spanned a maximum of 12 months.
“Intermittent fasting is not a miracle solution, but it can be one option among several for weight management,” said Dr. Luis Garegnani, lead author of the review and director of the Cochrane Associate Centre at the Italian hospital of Buenos Aires in Argentina. “Intermittent fasting likely yields results similar to traditional dietary approaches for weight loss. It doesn’t appear clearly better, but it’s not worse either.”
Intermittent fasting, which involves restricting eating to specific hours or fasting on certain days, has gained significant popularity in recent years, fueled by claims of weight loss, improved physical and cognitive health, and even slowed aging. The Cochrane review employed rigorous methodology to analyze evidence from randomized clinical trials involving 1,995 adults across Europe, North America, China, Australia, and South America. The trials examined various intermittent fasting methods, including alternate-day fasting, the 5:2 diet, and time-restricted eating.
Beyond the limited impact on weight loss, the researchers discovered no compelling evidence that intermittent fasting improved quality of life more effectively than other diets. Dr. Garegnani emphasized the need for clarity surrounding the evidence base for fasting diets, given their widespread promotion in the media and increasing adoption by the public. He noted that many existing studies are short-term and of limited quality, hindering the ability to draw definitive conclusions about potential benefits.
Surprisingly, none of the 22 studies analyzed assessed participant satisfaction with intermittent fasting, according to Dr. Garegnani.
Dr. Zhila Semnani-Azad, at the National University of Singapore, suggested that the benefits of intermittent fasting may be influenced by timing, given the close connection between the body’s circadian rhythms and metabolism. Animal studies indicate that fasting can alter how fat reserves are utilized, enhance insulin sensitivity – crucial for managing diabetes – and reduce inflammation and oxidative stress. She as well pointed to potential benefits for aging and longevity through autophagy, the body’s cellular recycling process.
Dr. Semnani-Azad also highlighted a challenge in understanding the effects of intermittent fasting: the lack of a universally accepted definition.
Maik Pietzner, a professor of health data modelling at the Berlin Institute of Health at Charité, expressed surprise at the small weight loss observed with fasting compared to doing nothing. However, he noted that this finding aligns with evidence suggesting reduced physical activity during fasting periods and the inherent difficulty of weight loss without pharmaceutical intervention. His own research indicates that short periods of complete fasting, even lasting up to two days, have minimal impact on the body, and more prolonged fasting is required to induce changes that could potentially lead to benefits.
In one study conducted by Pietzner’s team, participants consumed only water for seven days, but significant changes to proteins in their blood were not observed until after three days of fasting. “If people feel better on such diet regimens, I wouldn’t stop them, but this work, along with others in the field, clearly shows that there’s no robust evidence for positive effects beyond a possible moderate weight loss,” Pietzner said. “Our bodies have evolved under constant scarcity of food, and can deal really well with prolonged periods without it, but that does not mean that we perform any better once these evolutionary conserved programmes kick in.”
Dr. Michael Mosley, a British journalist, popularized the 5:2 diet after discovering it helped him reverse his type 2 diabetes in 2012, according to information from The Fast Diet website and Healthline. Mosley also advocated for time-restricted eating as a form of intermittent fasting.
