In a blow to believers in time-restricted eating — a form of intermittent fasting where people only eat during a restricted window during the day — researchers in China have found the method has no significant benefits compared with simple calorie restriction in battling obesity.
“Our data suggest that caloric intake restriction explained most of the beneficial effects of a time-restricted eating regimen,” according to researchers at Southern Medical University in Guangzhou, China.
The study, published this week in the New England Journal of Medicine, split 139 overweight to significantly obese adults in Guangzhou into two study groups that were followed for a year.
READ MORE: Your smartwatch could detect COVID-19 symptoms before you do
One group was told to limit their daily food intake to 1,500 to 1,800 calories a day for men, and 1,200 to 1,500 calories a day for women. Men and women in the other group were told to eat the same amount of calories, but to eat only between the hours of 8am and 4pm.
To track compliance, study participants were asked to keep food diaries and photograph all food they ate.
At the end of the year, both groups lost weight — about 6.4 to 8.2 kilograms — but eating on a time-restricted schedule didn’t produce any significant difference in weight loss between the two groups.
Nor was there any real difference in other markers of weight loss, such as BMI (body mass index, a popular way of measuring weight), waist circumference, body fat or metabolic risk factors such as insulin resistance and blood pressure.
READ MORE: All the best workout hacks you need to know
“Bottom line, the determinant of weight loss, as well as reductions in body fat, visceral fat, blood pressure, and glucose and lipid levels, is dependent on reducing calorie intake, regardless of the distribution of food and beverages consumed throughout the day,” said Alice Lichtenstein, director and senior scientist at Tufts University’s Cardiovascular Nutrition Laboratory. She was not involved in the study.
Prior research showed benefits
Prior research had shown advantages to time restriction. A 2020 review of human and animal studies had found benefits to restricting calories to a shortened period of the day, including a reduction in blood pressure, weight loss and improved longevity.
However, a number of those studies were in mice and those in humans were of much shorter duration, mere months.
The results of the year-long clinical trial are not surprising, said Dr. David Katz, a specialist in preventive and lifestyle medicine and nutrition, who was not involved in the study.
READ MORE: What is your diet personality?
“Restricting time instead of calories does not contribute metabolic magic; rather, it is a form of discipline that helps to control calories,” said Katz.
“My favourite approach is to focus on the quality of foods and diet, and then let quantity control take care of itself. A diet made up mostly of whole, wholesome plant foods is intrinsically satiating at low calorie levels,” he said.
Lichtenstein added: “Decisions on the approach used to restrict calorie intake should be determined by what works best for an individual within the context of their lifestyle. The most important factor is identifying an approach that is sustainable in the long term.”
This story was originally published by CNN and has been republished here with permission.
For a daily dose of 9Honey, subscribe to our newsletter here.
