If you’re trying to lose weight and you’re sick of watching what you eat, researchers have some good news: You can watch the clock instead.
In a yearlong study, people who didn’t change what they ate — but ate it all between noon and 8 p.m. — achieved significant, sustained weight loss that was comparable to people who paid close attention to their food choices in order to cut their daily calories by 25%.
Dieters in both groups lost about 4% of their body weight after a year, researchers reported Monday in the Annals of Internal Medicine. Meanwhile, people in a control group who made no changes to their eating habits gained about 1% of their body weight in those same 12 months.
The study is the first in the U.S. to compare the two weight-loss methods head to head, said senior author Krista Varady, a nutrition researcher at the University of Illinois Chicago. Though both yielded similar results, the one that emphasized time instead of calories “is an easier diet to adhere to,” she said.
As our waistlines continue to grow, so does interest in dieting. A whopping 49% of Americans try to lose weight each year, according to the CDC. That includes 56% of women and 42% of men.
The tried-and-true way to lose weight is to burn more calories than you consume. But that’s easier said than done. Preparing low-calorie meals and keeping track of portion sizes can be expensive and time consuming, Dr. Adam Gilden and Dr. Victoria Catenacci of the University of Colorado School of Medicine wrote in an editorial that accompanies the study. It also requires a lot of discipline — not many people can withstand the temptation of a slice of cake on a co-worker’s birthday or a meal out with friends on the weekend.
In recent years, time-restricted eating (or TRE) has emerged as a popular alternative for losing weight. The idea is to compress your eating day into six or eight hours in order to reduce the amount of insulin your body produces. That’s important, because insulin prompts the body to store fat. In addition, studies have shown that people following a TRE regimen consume fewer calories each day.
TRE, a version of intermittent fasting, is certainly simpler than counting calories. But are the results the same?
To find out, Varady and her colleagues recruited 90 people who were obese and randomly assigned them to one of three groups.
The first group was asked to do all of their eating between noon and 8 p.m., then fast for the next 16 hours. (They were allowed to drink water, tea, coffee or up to two diet sodas during the fasting period.)
The second group was asked to reduce their caloric intake by 25%, or about 500 calories on average. People in both of these groups met with dietitians to help them follow nutrition advice from the American Diabetes Assn. The people counting calories also used this time to plan meals based on their food preferences.
The third group of participants was asked to stick with their usual eating and exercise routines.
After six months, the people in the TRE group lost an average of 8.8 pounds (4 kilograms) and those counting calories dropped an average of 11.2 pounds (5.1 kilos). The difference between the two groups wasn’t statistically significant.
The dieters spent the next six months in weight-maintenance mode. For the TRE group, that meant expanding their eating window to between 10 a.m. and 8 p.m. For the calorie counters, it meant increasing their caloric intake based on their new energy needs in order to maintain their weight. In both cases, they learned cognitive behavioral strategies to keep them from backsliding.
After a year, the people in the TRE group were still 7.7 pounds (3.5 kilos) lighter than when they started out, and those tracking their calories maintained 9.5 pounds (4.3 kilos) of their weight loss. Again, the difference between the two groups wasn’t statistically significant. However, both dieting groups fared much better than the control group, whose members actually gained weight (around 2.4 pounds or 1.1 kilos) over the year, according to the study.
More than 80% of the study participants were women, one-third were Black and 46% were Latino. Although this sampling does not represent the U.S. as a whole, Black and Latino Americans are more likely than white and Asian Americans to be obese. That makes the findings difficult to extrapolate to the population as a whole.
It’s not clear whether people who are overweight but not obese would see the same results with TRE, though Varady said she suspects it would still work, though perhaps to a lesser extent.
Motivated people who want to lose weight can see positive results with either method, Varady added. But in terms of accessibility and time commitment, time-restricted diets could be a better option.
“It is a simple diet,” she said. “You don’t need to buy expensive products or change things out in your pantry. You just have to decide on a time window and stick to it for as long as you can.”
In an interview, Gilden said he wasn’t convinced that people without access to professional dietitians would see the same benefits from TRE.
Varady said her team would continue to follow the study participants to see if they can maintain their weight loss for another year.