June 29, 2023 – Fasting for 8 hours is as good as counting calories for weight loss, new research shows.
The study, published Monday in the Annals of Internal Medicine, found that people with obesity lost 10 pounds through intermittent fasting, compared to 12 pounds through calorie restriction. The statistical analysis found no significant difference between the two groups’ weight loss.
Most of the people in the study were female and weighed around 220 pounds at the start of the trial. A total of 77 people were split into three groups: One was told to fast for 8 hours, another was told to restrict their calories, and the third ate as they normally would.
The people who fasted and restricted calories were in a weight loss phase for 6 months – the intermittent fasting group could eat anything they wanted between noon and 8 p.m., and didn’t have to cut their calories.
The calorie restriction group had to cut 25% of their daily calorie intake. They were also told to fill half of every plate with fruits or vegetables, and consume about half their calories as carbohydrates, 30% as fat, and 20% as protein.
For 6 months after that, both groups were in a weight maintenance phase. The intermittent fasting group could eat from 10 a.m. to 8 p.m., and the calorie restriction group was told to match their diet with their energy needs.
The people in the study met regularly with dietitians – a part of the trial that experts say could have made the effects of fasting more pronounced than in previous studies.
An earlier, shorter trial found that people lost about 2 pounds after 12 weeks of intermittent fasting, a more modest result, compared to the 9 pounds that lost after 6 months in this trial.
Intermittent fasting, or time-restricted eating, is a catch-all for eating patterns that could include several full days of fasting per week or time-restricted eating during the day.
The effect of having less time to eat is thought to lead to eating fewer calories, and therefore losing weight. This trial found the intermittent fasting group ate 425 fewer calories per day and 20 calories less than the calorie-restricted group.
“Time-restricted eating is undoubtedly an attractive approach to weight loss in that it does not require the purchase of expensive food products, allows persons to continue consuming familiar foods, and omits complicated calorie tracking,” Shuhao Lin, a registered dietitian at the University of Illinois, Chicago, and colleagues write in the paper.