When it comes to losing weight, the amount of food you eat probably matters more than the timing of your meals, according to a study published Wednesday in the Journal of the American Heart Association.
Researchers at Johns Hopkins University asked 547 people to record their meal sizes and when they ate on a mobile app daily for six months. The scientists then looked at how much the participants weighed over the course of about six years, more than five years before they started recording their meals and about six months afterward, using electronic health records.
The study separated the recorded meals into three size categories: a small meal had fewer than 500 calories, medium meals had between 500 and 1,000 calories, and large meals had more than 1,000. Overall, the results showed that participants who ate the most large and medium meals gained weight over six years, while those who ate fewer smaller meals lost weight.
That is consistent with the long-standing and well-understood rule that eat fewer calories contributes to weight loss.
The researchers did not find a link between weight change and the practice of limiting food intake to a specific period of time, often referred to as intermittent fasting. They also found no association between weight change and the timing of a person’s first meal after waking up or last meal or snack before bed.
«This study shows that changing the timing of meals will not prevent slow weight gain for many, many years, and that probably the most effective strategy is to really control how much you eat and eat fewer large and smaller meals,» said Dr. Wendy Bennett, study author and associate professor at Johns Hopkins Medicine.
The study included people of various weights, including those who were severely overweight or obese. However, the weight changes observed were small overall: People who ate one extra daily meal saw less than 1 pound of extra weight gain per year, on average, relative to people who didn’t eat that extra meal.
«The effect is so small that I wouldn’t tell anyone to change what they’re doing,» said Courtney Peterson, an associate professor of nutritional sciences at the University of Alabama at Birmingham, who was not involved in the research.
Bennett, however, said his study provides evidence that restricting meal sizes can be effective for weight loss, even after adjusting for people’s starting weight. (People who are heavier tend to have an easier time gaining or losing pounds.)
He also noted that the average person gains 1 to 2 pounds per year, which can equate to significant weight gain over time. Eating fewer big meals and more small meals, then, could «prevent that slow weight gain,» Bennett said.
But Peterson said he doesn’t see the study as «a no-brainer» when it comes to determining the best weight-loss strategy.
Other research has found that the timing of a person’s first meal of the day may matter: a study published in October found that eating earlier in the day may contribute to weight loss, perhaps because it helps people burn calories or feel fuller throughout the day.
On average, the participants in Bennett’s study ate over a period of 11.5 hours, with their first meal less than two hours after waking up and their last around four hours before bedtime.
To better test whether intermittent fasting can help with weight loss, Peterson said, researchers need to directly compare people who limit their food intake to a specific period with those who don’t in a controlled trial.
Previous studies with that type of design have produced mixed results. Some research suggests that fasting every other day, or restricting calories two days a week, could help people with obesity lose weight. But other studies They have found that restricting eating to certain periods of time does not reduce body weight any more than restricting daily calorie intake.
«I think time-restricted eating can be really helpful when it helps people restrict their calories,» Bennett said. «We already know that caloric restriction is the most effective weight loss strategy.»
Peterson also emphasized that the nutritional quality of a person’s diet It influences whether they gain or lose weight. Eating too many highly processed foods like hot dogs, French fries, or soda can contribute to weight gain, while diets that are based on vegetables and whole grains can help with weight loss.
«Some of our best human data suggest that diet quality probably matters more than meal timing,» Peterson said.