Dieters should limit themselves to only eating between 7am and 3pm to lose more weight, a study suggests.
Intermittent fasting is a popular dieting technique where a person can eat as much as they like, of whatever they like, within a set time frame every day.
On its own it is a potent weight-loss tool, but when also combined with a healthy calorie-controlled diet the method can be highly effective at shifting pounds, shrinking waistlines and improving health.
Researchers from the University of Alabama at Birmingham recruited 90 obese individuals and put all of them on a diet, with half also told they can only eat for eight hours a day between 7am and 3pm.
Both groups received expert guidance on how to follow a diet, were told to stick to it for at least six days a week, and to do between 75 and 150 minutes of exercise a week.
Blood pressure improved
The study found that people who stopped eating at 3pm lost almost a stone over 14 weeks, while the control group lost only about nine pounds. The researchers found that combining a diet with the time restriction equates to losing around an extra five pounds.
“The effects of [time-restricted eating and calorie restriction] were equivalent to reducing calorie intake by an additional 214 calories per day,” the scientists wrote in their paper, published in JAMA Internal Medicine.
Data also show that blood pressure was improved because of fasting along with the moods of the participants.
The researchers said the routine of stopping eating at 3pm was “feasible” and people managed to stick to it despite having social commitments in the evening and full-time jobs.
“We found that [early time-restricted eating] was acceptable for many patients. About 41 per cent of completers in the control group planned to continue practising [early time-restricted eating] after the study concluded,” the authors write.
But with modern-day schedules and the trend to eat late into the evening, some experts believe a later window of eating may be the best intermittent fasting approach.
Watch: What is intermittent fasting and how does it work?
Tim Spector, professor of genetic epidemiology at King’s College London, for example, believes people should have breakfast no later than 11am as this means that if a person is eating at 8pm or 9pm they will still have a significant window of fasting.
“There are still people, particularly in the north of England, who eat earlier but generally we have moved towards continental eating habits, having dinner much later like people in Spain and Italy,” he said in June at the Cheltenham Science Festival.
“Even those who don’t do that may end up snacking up until 9pm, making it difficult to achieve a 14-hour fasting period.
“There is a simple change people can make by shifting their breakfast from 8am to 11am, which actually is more effective than more fashionable fasting diets like 5:2.”
Findings not conclusive
However, the researchers focused on an early window and said that their positive findings are not yet enough to conclusively rule that intermittent fasting is a good thing.
A Chinese study earlier this year found there was no benefit over a 12-month period, and experts are calling for much larger studies.
“The inconsistency… highlights the need for larger-scale studies to provide more robust evidence of the potential clinical benefits for weight loss and cardiometabolic health for those with overweight and obesity,” said Dr Simon Steenson, a nutrition scientist at the British Nutrition Foundation, who was not involved with the study.
“It remains difficult to say with any certainty if time-restricted feeding is a superior approach to weight loss than eating fewer calories throughout the day,” he added.
Also commenting on the findings was Prof Peter Hajek, of Queen Mary University London, who said the major gap in the research is now whether the short-term benefits of intermittent fasting can be sustained.
“Time-restricted eating is an exceptionally simple and practicable intervention that may have a better potential for being manageable over the long term than most alternative methods,” he said.
“A proper large trial of time-restricted eating on its own with long-term follow-up is now needed.”