Here's What That Controversial New Study on Time-Restricted Eating Really Shows

The results of a new weight loss study were published this week, leading to headlines proclaiming that intermittent fasting isn't a magic diet trick.

The researchers wanted to see if adding a restriction on when you can eat led to greater weight loss compared to just following a low calories diet.

They recruited people with an average weight of194 lbs and a age of 32 years.

The participants were randomized to follow either the low calories diet that had reduced their daily energy intake by 25 percent or the same low calories diet with the addition of a time period during which they were allowed to eat.

This approach is called time-restricted eating or intermittent fast. Both groups received support from health coaches to follow their diet.

After one year, people in both groups lost about 7 percent of their body weight. The low calories group lost an average of 6.3 kilograms, while the low calories plus time restricted group lost 8 kilograms.

There was a 1.8 kilogram difference between the groups, but it was not statistically significant.

There were no significant differences between the groups when it came to improved blood sugar and blood fat levels.

The weight loss trial is important.

In the United States, most intermittent fast studies have been conducted. This trial was done in China and recruited people in Guangzhou, so it provides important data using a culturally sensitive, prescribed calorie restriction over a year.

2. It showed small extra time restrictions on eating don't make much difference

The participants in Guangzhou usually had a window of about 10 hours to eat. In the US, 90 percent of adults have an eating window of 12 hours, with only 10 percent having an overnight fast greater than 12 hours.

The overnight fast in the US is less than nine hours, meaning that more than 50 percent of people eat over 15 hours a day.

In the current study, the time restriction on eating was about two hours less per day than it is in China. This wouldn't have been much different from usual.

In China, the biggest meal is usually eaten in the middle of the day, so that was not influenced by the time restriction. In countries where the evening meal is the biggest or people snack all evening, time restriction may still be a beneficial way to reduce intake.

A 2020 review of 19 studies that used time-restricted intermittent fasting found it was an effective treatment for adults with obesity, leading to greater loss of body weight and body fat, with significantly lower systolic blood pressure and blood sugar.

The groups in the trial were given a lot of support to follow the diet. They were provided with one meal replacement shake per day for the first six months to make it easier to follow the kilojoule restriction.

They received diet counseling from health coaches during the trial. They received booklets with information on portion size and sample menus.

They were required to keep a daily log with photographs of foods eaten and the time, using the study app, as they were encouraged to weigh foods to improve their accuracy in reporting kilojoule intakes.

They received follow-up calls twice a week and met with the health coach every two weeks for the first six months.

In the second half of the year, they continued to fill out their records for three days per week, received weekly follow-up calls, and met with a health coach monthly. They attended monthly health education sessions.

This was a lot of support. Long-term support to achieve health behavior changes can lead to a weight loss of 3-6 percent of body weight, which can lead to a 50 percent lower risk of developing type 2 diabetes over eight years.

Even though adherence was high in the trial, individual weight loss responses were very variable.

84 percent of participants followed the prescribed daily calories targets. The low calories only group lost weight at a rate of 7.8 to 4.7 kilograms, while the low calories plus time restricted eating group lost weight at a rate of 6.4 to 6.9 kilograms.

The study confirms that there is no one best diet for weight loss. It shows that small decreases in the window of time you are eating probably won't make a difference to weight loss.

The Laureate Professor in Nutrition and Dietetics is Clare Collins.

This article is free to use under a Creative Commons license. The original article is worth a read.