For decades, common wisdom held that how much we eat and exercise determines our weight. As researchers learned more about the human body, they discovered that what people eat also plays an important role in weight gain and loss. This led to a wide range of dietary recommendations that have changed over time: Don’t eat fats. Avoid sugars. Eat protein at every meal.
Now researchers are discovering another factor that influences health and weight gain: When we eat. A growing body of evidence finds that the time of day when we consume calories affects weight gain and overall health.
The most recent study to support this idea — published this summer in the Journal of Nutrition — followed 96,000 Seventh-day Adventists in the U.S. and Canada. Data from the study came from broad questionnaires that explore the links between lifestyle, diet, and disease among members of the group.
Researchers found that participants who ate three meals a day and snacked between meals tended to gain weight over time, while those who ate one or two meals a day tended to lose weight.
What was more insightful was the finding that participants who made breakfast their largest meal were less likely to be overweight or obese compared to those who ate their largest meal at lunch or dinner. And those who ate breakfast were more likely to be a healthy weight than those who skipped breakfast.
An earlier study, published in the journal Obesity, found similar results. Researchers recruited 93 overweight and obese women and put them on prescribed diets for 12 weeks.
In this study, all of the women consumed 1,400 calories a day, but one group consumed its largest meal at breakfast, while another consumed its largest meal at dinner. Regardless of the time of day, participants ate the same healthy foods at their largest meal.
After 12 weeks, women in both groups lost weight, but those who ate their biggest meal in the morning lost significantly more — two and a half times as much as women who ate large dinners. Big-breakfast eaters also saw improvements in other areas, such as belly fat, hunger levels, and fasting blood sugar levels, which is used to test for diabetes.
The evidence on the benefits of having a big breakfast is strong enough that the American Heart Association has issued a statement that planning and timing meals and snacks is a healthier way of eating, and likely reduces the risk factors for heart disease. The group's statement underscored that eating breakfast is helpful in preventing obesity and diabetes.
“Meal timing may affect health due to its impact on the body’s internal clock,” said Marie-Pierre St-Onge, Ph.D., writing group chair and an associate professor of nutritional medicine at Columbia University. She also explained that planning meals and snacks can help prevent emotional eating: “Many people find that emotions can trigger eating episodes when they are not hungry, which often leads to eating too many calories from foods that have low nutritional value."
The take-home message is pretty clear: Breakfast truly may be the most important meal of the day, and consuming more calories in the morning and fewer as the day goes on is an effective way to maintain a healthy weight.
Kahleova, H., Lloren, J. I., Mashchak, A., Hill, M., & Fraser, G. E. (2017). Meal Frequency and Timing Are Associated with Changes in Body Mass Index in Adventist Health Study 2. The Journal of Nutrition. doi:10.3945/jn.116.244749