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People who fasted three days a week lost more than 50 per cent more weight than counterparts on a regular reduced-calorie diet, according to research on the best ways to combat obesity.
The intermittent fasters shed 7.6 per cent of their body mass over one year versus 5 per cent for those on the restricted daily intake, suggesting that this pattern of food abstinence might be a more effective approach for weight loss.
Dieting strategies are of growing interest to health authorities as well as individuals, after a surge in obesity over the past 30 years that is estimated to affect more than 1bn people worldwide.
“We think fasting three days a week might be a sort of sweet spot for weight loss,” said Victoria Catenacci, the research’s co-lead author and an associate professor at the University of Colorado Anschutz Medical Campus.
“More fasting days per week may be too rigid and difficult to stick to, while fewer may not produce enough of a calorie deficit to outperform daily calorie restriction diets.”
The research examined 165 overweight or obese people and split them into two diet regime groups, according to a paper published in the Annals of Internal Medicine on Monday.
The three-day-a-week fasters — known as the 4:3 group — went on a diet to reduce their energy intake by 80 per cent from a set baseline on those days. Their calorie intake for the remaining four days was not limited, although they were encouraged to make healthy food choices.
The reduced-calorie group members were prescribed a goal to create an energy deficit of 34.3 per cent each day. This meant both groups should have been operating at an equal energy deficit over the course of each week.
The researchers gave all participants behavioural support, free gym membership and encouraged them to exercise for at least 300 minutes per week.
The intermittent fasters lost 7.7kg over the course of the year, versus 4.8kg for the calorie restrictors, the researchers said. Just under 20 per cent of the intermittent fasters dropped out, compared with almost 30 per cent of the other group.
One potentially appealing feature of the 4:3 system was that dieters did not have to focus on counting calories, the researchers said. Another was that the unrestricted eating days might make the regime easier compared with the constant hunger experienced when sticking to daily calorie limits.
Soaring global obesity rates have piled costs on health systems and driven huge demand for weight-loss drugs such as Ozempic, Wegovy and Mounjaro. But the long-term effects of the medicines are still unclear, while their cost puts them out of reach of some potential users.
The continued need for non-pharmaceutical weight-loss strategies has driven a search for what is most effective. Intermittent daily fasting approaches have grown in popularity, including the so-called 5:2 diet and the stricter alternate-day regime. Other approaches cut out food intake for certain periods during each day.
The latest study reaffirmed that intermittent energy restriction could be an “effective and sustainable weight loss intervention”, said Adam Collins, associate professor of nutrition at the University of Surrey.
Earlier research on intermittent fasting had suggested it created a conscious or subconscious tendency for some people to eat less than they normally would on non-fasting days too, added Collins, who was not involved in the research.
“This may explain why the 4:3 group were closer to the calorie deficit target overall,” Collins said. “[It] does support the notion that, in the real world, intermittent energy restriction protocols outperform conventional everyday calorie restriction both in terms of compliance and results.”
