Intermittent fasting has gained immense popularity as a weight loss method, with many believing it offers significant advantages over traditional diets. However, a comprehensive review of scientific studies reveals that intermittent fasting may not be any more effective for weight loss than standard dieting methods, and it is only marginally better than not dieting at all.
The research team evaluated 22 studies conducted worldwide, concluding that individuals who are overweight or living with obesity achieved similar weight loss results through conventional dietary guidelines and fasting strategies like the 5:2 diet, which was brought to mainstream attention by Michael Mosley.
The review findings indicate that fasting resulted in an average weight loss of only about 3% of body weight, which falls short of the 5% threshold considered clinically significant by healthcare professionals. Most of the studies assessed were short-term, lasting a maximum of 12 months.
“Intermittent fasting should not be regarded as a miracle cure, but it can serve as one of several options for managing weight,” stated Dr. Luis Garegnani, the lead author and director of the Cochrane Associate Centre at the Italian hospital of Buenos Aires in Argentina. “The effects of intermittent fasting on weight loss appear to be comparable to those of traditional dietary methods. It doesn’t seem to provide any clear advantages, but it isn’t worse either.”
Intermittent fasting involves restricting eating to specific time windows or fasting on designated days. Its appeal has surged due to claims that it aids weight loss, enhances physical and mental well-being, and may even slow the aging process.
The Cochrane review utilized rigorous methodologies to analyze data from randomized clinical trials involving 1,995 adults across Europe, North America, China, Australia, and South America. The trials evaluated various intermittent fasting approaches, including alternate-day fasting, the 5:2 diet, and time-restricted eating.
Beyond the modest benefits for weight loss, the review found no substantial evidence suggesting that intermittent fasting significantly enhances quality of life more than other dietary strategies.
Dr. Garegnani emphasized the need to clarify the evidence surrounding fasting diets, especially given their immense popularity and frequent promotion in the media. Many of the studies are short-lived and lack quality, making it difficult to draw firm conclusions regarding potential benefits. Notably, none of the 22 studies assessed participants’ satisfaction with intermittent fasting.
Dr. Zhila Semnani-Azad from the National University of Singapore noted that the effectiveness of intermittent fasting might be influenced by meal timing because the body’s circadian rhythms are closely linked to metabolism. Animal studies have indicated that fasting can alter how fat reserves are utilized, enhance insulin sensitivity—important for diabetes management—and diminish inflammation and oxidative stress. She mentioned that it could also benefit aging and longevity by initiating a process known as autophagy, the body’s recycling mechanism. However, she pointed out that the lack of a universal definition for intermittent fasting complicates understanding its impacts.
Maik Pietzner, a professor of health data modeling at the Berlin Institute of Health at Charité, expressed surprise at the limited weight loss associated with fasting compared to no dieting. He explained that this aligns with evidence indicating that individuals are less physically active while fasting, and that achieving weight loss without pharmacological aids is challenging.
His findings support the notion that short periods of total fasting, even lasting up to two days, have minimal effects on our physiology, suggesting that longer fasting durations may be necessary for observable benefits. In one study, participants who consumed only water for a week observed significant changes to blood proteins only after three days.
“If individuals feel better on such fasting regimens, I wouldn’t discourage them, but this research, along with others in the field, clearly demonstrates that there’s no strong evidence for beneficial effects beyond moderate weight loss,” Pietzner commented. “Our bodies have evolved to cope with extended periods of food scarcity, but that does not mean we perform better once these deeply embedded evolutionary mechanisms are activated.”
