A number of studies have suggested that eating only during a limited window of time can help some people lose weight. But it’s unclear why: Does the strategy just help people eat less, or is there something beneficial about keeping meals within a shorter time frame?
New research falls in the former camp, suggesting that the amount of calories people consume matters more than the timing.
A small, randomized trial at Johns Hopkins University School of Medicine — the results of which were published Friday in the journal Annals of Internal Medicine — found that when researchers controlled the number of calories people consumed, both time-restricted and regular eating schedules resulted in similar degrees of weight loss.
“It makes us think that people who benefit from time-restricted eating — meaning they lose weight — it’s probably from them eating fewer calories because their time window’s shorter and not something else,” said the study’s lead author, Dr. Nisa Maruthur, an associate professor of medicine at Johns Hopkins University.
Time-restricted eating regimens vary, and some are similar to intermittent fasting, a type of diet that involves alternating between periods of fasting and eating. The new trial looked at a 10-hour eating window, which is longer than what would typically qualify as intermittent fasting.
The researchers supplied 41 people with prepared meals for 12 weeks. The participants, most of them Black women, had obesity and were either prediabetic or diabetic.
Their meals (breakfast, lunch, dinner and a snack) were designed to contain the same number of calories they ate in their daily lives, based on their age, sex, weight, height and level of physical activity. The food had a healthy balance of fat, carbohydrates and protein.
On a given day, participants might have cereal and a fruit cup for breakfast, a kale salad with white beans and lentils for lunch, peanuts or mandarin oranges for a snack and a beef stew for dinner.
Half the group ate meals over a 10-hour window, from 8 a.m. to 6 p.m. Around 80% of their calories were consumed at breakfast and lunch, because some research has suggested that eating most of your calories early in the day could be beneficial for weight loss.
The other half ate from 8 a.m. to midnight and consumed half of their daily calories at dinner — a schedule meant to mimic many people’s eating patterns outside a research setting.
During the eating windows, the trial didn’t limit beverages if they were calorie- and caffeine-free. Participants were also each allowed one cup of coffee, diet soda and alcoholic beverage per day. Outside the designated time periods, only water was allowed.
At the end of the study, participants lost roughly the same amount of weight regardless of which regimen they followed. The average in the time-restricted eating group was around 5.1 pounds lost, compared to 5.7 pounds for the other group. There were no significant differences in blood sugar, blood pressure, waist circumference or lipid levels.
The results were similar to the findings of a randomized trial last year, which found that intermittent fasting was similar to calorie counting as a weight loss strategy.
However, research overall on time-restricted eating is mixed: A six-year study didn’t find a link between weight change and limiting food intake to a specific time window.
The new trial was distinctive in that the researchers controlled what all participants ate — a rarer and more complex experiment design.
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