A trendy form of intermittent fasting appears to be helping people lose some weight — though it may not be any better than old-fashioned calorie counting, a new clinical trial suggests.
Researchers found that the tactic, called time-restricted eating, helped obese people lose an average of about 8 pounds in a year. That was consistent with a second study group taking the traditional route of calorie counting and portion control.
Time-restricted eating is a form of intermittent fasting in which people limit themselves to eating within a certain time frame each day. Outside that window, they swear off everything except zero-calorie drinks.
The main selling point of time-restricted eating is its simplicity: instead of laboriously counting calories, people just have to look at the clock. And small studies have shown that limited eating windows — 6 hours is popular — can help people eat less and shed some pounds.
The new trial adds to the story because it was intended to be as realistic as possible, senior researcher said Krista Varadia professor of nutrition at the University of Illinois Chicago.
Participants were allowed to eat during an 8-hour time span, from noon to 8 p.m., which allowed them to eat with family or go to a restaurant with friends. And they just kept to that time window, without having to cut out certain foods or measure strict portion sizes.
Previous studies of time restriction have led people to take extra steps, such as tracking calories.
But that misses the mark, Varady said, because people try timed eating to keep it easy.
“I think it’s become so popular because it’s simple, accessible and free,” she said.
So for their trial, Varady and her colleagues recruited 90 obese adults who wanted to lose weight. The majority were black or Hispanic – two groups that are often underrepresented in clinical trials.
Each participant was randomly assigned to one of three groups: one started with the time-restricted plan, a second focused on calorie counting, and the third made no changes and served as a control group.
The calorie counters aimed to reduce their daily calories by 25% and met with a dietitian to make healthy food choices. The time-restricted group, meanwhile, went on the clock: For the first six months, they limited their eating window from noon to 8 p.m.; for the next six months, they were allowed to extend it to 10 a.m. to 8 p.m
Both diet groups also had periodic phone or video calls with a dietitian to talk about overall healthy eating.
In the end, the two groups fared similarly. After a year, the people in the control group had gained weight, averaging about 2.5 pounds. But those in the diet groups lost an average of about 8 to 9.5 pounds.
The findings were published June 26 in the Annals of Internal Medicine.
“I don’t think intermittent fasting works any better than other diets,” Varady stressed. But the findings show that if people stick to the tactic, they can keep losing weight.
Dr. Adam Gildenan associate professor at the Anschutz Medical Campus of the University of Colorado, co-wrote an editorial published in conjunction with the study.
He said it’s his experience that patients ask about time-restricted eating “all the time.” But it’s important, Gilden said, not to overstate the ease of the approach.
“There’s nothing magical about it,” Gilden said. “You still need to put some work into it.”
He noted that the trial participants did receive help, in the form of regular nutritional counseling sessions – and that may have been a key ingredient in their weight loss.
“I think support is the most important part,” Gilden said.
Varady said that while people can certainly apply time constraints on their own, they could be more successful if they have support. That could be from a dietitian, she said, or from a group like Weight Watchers.
One problem with time restriction is that it focuses on limiting food intake and not making healthier food choices.
“What we saw is that people’s nutritional quality isn’t getting better, but it’s not getting worse either,” Varady said.
She added that changing diet quality is “the hardest part” because people’s food preferences are so ingrained and factors such as income and access to healthy food come into play.
Ideally, though, eating healthier should be the goal, Gilden said.
He suggested that people who want to lose weight start with some form of support, such as talking to their doctor (who may refer them to a dietician).
Time constraints are not for everyone. According to Varady, people may experience headaches, nausea, or dizziness initially as the body adjusts to the new eating schedule — and some give up.
It’s also considered inappropriate for certain groups, such as pregnant women, people with a history of eating disorders, and people taking medications that need to be timed with food.
More information:
Time-restricted eating without counting calories for weight loss in a racially diverse population, Annals of Internal Medicine (2023). DOI: 10.7326/M23-0052
Time-restricted eating for obesity treatment? The devil is in the (counseling) details, Annals of Internal Medicine (2023). www.acpjournals.org/doi/10.7326/M23-1396
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