Several studies have suggested that eating only for a limited period of time can help some people lose weight. But it's not clear why: Does the strategy just help you eat less, or is there something beneficial about keeping meals within a shorter time frame?
A new study favors the first scenario and suggests that the amount of calories consumed is more important than the schedule.
A small randomized trial at Johns Hopkins University School of Medicine – the results of which were published Friday in the Annals of Internal Medicine – found that when researchers monitored the number of calories people consumed, both restricted schedules as regular ones resulted in similar degrees of weight loss.
“This makes us think that people who benefit from time restriction, that is, who lose weight, probably do so because they consume fewer calories because their time frame is shorter and not because of anything else,” said the author. lead author of the study, Dr. Nisa Maruthur, associate professor of Medicine at Johns Hopkins University.
Time restriction regimens vary, and some are similar to intermittent fasting, a type of diet that consists of alternating periods of fasting and eating. The new trial looked at a 10-hour eating window, which is longer than what is typically considered intermittent fasting.
The researchers provided prepared meals to 41 people for 12 weeks. The participants, mostly black women, were obese and prediabetic or diabetic.
Their meals (breakfast, lunch, dinner and a snack) were designed to contain the same number of calories as they ate in their daily lives, based on their age, sex, weight, height and level of physical activity. The meal had a healthy balance of fats, carbohydrates and protein.
On a given day, participants could have cereal and a cup of fruit for breakfast, a coleslaw with white beans and lentils for lunch, a snack of peanuts or mandarin oranges, and a beef stew for dinner.
About 80% of calories were consumed at breakfast and lunch, as some research suggests that eating most of your calories early in the day may 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 intended to mimic the eating patterns of many people.
During mealtimes, the trial did not limit drinks if they did not contain calories or caffeine. Participants were also allowed to have one cup of coffee, one light soda, and one alcoholic beverage per day. Outside of the designated periods, only water was allowed to be drunk.
At the end of the study, participants lost about the same amount of weight regardless of which regimen they followed. The average in the time-restricted eating group was about 5.1 pounds lost, compared to 5.7 pounds in the other group. There were no significant differences in blood sugar levels, blood pressure, waist circumference or lipids.
The results were similar to those of a randomized trial last year, which found that intermittent fasting was similar to calorie counting as a weight loss strategy.
However, the overall research on time-restricted eating is mixed: One six-year study found no relationship between weight change and limiting food intake to a specific time interval.
The new trial was distinguished by the fact that the researchers controlled what all participants ate, a less common and more complex experimental design.
But their results come with some caveats, explained Dr. Lisa Chow, a professor of medicine at the University of Minnesota, who was not involved in the study.
The trial may not have captured the long-term benefits of time restrictions, he said. One of their studies, published last year, found that six months of time restriction—from noon to 8 p.m.—was more effective for weight loss than calorie restriction in people with type 2 diabetes. Additionally, Chow added, the trial may not have captured the long-term benefits of time restriction.
What's more, Chow explained that the study did not reflect what time restriction is like in real life, because it controlled people's calories and meals.
“When you talk about the doctor talking to a patient about weight loss, it is not the same, because the doctor is not going to provide all the food,” he stressed.
Other researchers also believe that meal timing is important for weight loss.
According to Satchin Panda, a professor at the Salk Institute for Biological Studies, the ideal restricted eating schedule involves waiting one to two hours after waking up to consume the first meal, and eating the last three hours before bedtime.
“It doesn't depend on the world clock, but on the internal one,” Panda explained. “For a person who wakes up at 6 am, it may be okay to start eating at 8 am. But the person who wakes up at 8 am can start eating at 9 am or 10 am.”
This is because the stress hormone cortisol is high after waking up, and melatonin – a hormone that regulates sleep – continues to decrease at that time. Because of this, people may find it more difficult to digest well soon after waking up, Panda explained.
On the other hand, eating close to bedtime can disrupt sleep, and insufficient sleep can increase cravings, Panda added. Some research also suggests that eating late at night may cause people to store more energy as fat.
Time restriction can also offer other benefits besides weight loss.
Panda's research found that this method can reduce so-called “bad cholesterol” and improve blood pressure and blood sugar in people with certain chronic diseases.
Separately, a study published last month found that restricting food consumption to less than eight hours a day may increase the risk of long-term cardiovascular death.
At least, according to Panda, time-restricted eating may offer an easier alternative to calorie counting.
“It's easier to count time than calories,” he said. “I guess most people can't remember how many calories they've consumed, but time is easy to remember.”
