According to a new study losing weight may not be just about what patients eat but when they eat it. Participants in the study who ate a bigger meal later in the day lost less weight than those who ate earlier.
Study author Dr. Frank Scheer, director of the medical chronobiology program at Brigham and Women’s Hospital in Boston, and his colleagues followed 420 people in Spain during a 20-week weight loss treatment program.
The participants were split into two groups — early eaters who ate lunch before 3 p.m. and late eaters who ate lunch after 3 p.m. In Spain, lunch is the biggest meal of the day, comprising about 40 percent of a person’s daily calories.
The early eaters, on average, lost 25 percent more weight than the late eaters over the course of the study.
The study authors found no difference in the groups’ weight loss based on breakfast and dinner timing. They also looked at energy expenditure, dietary composition, appetite hormones and sleep duration. These factors were similar in both groups, leading the authors to conclude that the timing of the large meal was the source of the sluggish weight loss.
The majority of cells in a human body run on a 24-hour schedule, Scheer says. The combination of all these body clocks is called the circadian system, and it’s controlled by a group of cells in the brain’s hypothalamus. But the "clocks" in individual organs’ cells can be altered by daily activity that doesn’t affect the control center.
For instance, researchers have found that feeding animals during abnormal times can "reset" the clocks in their liver and pancreas, which are key to optimizing metabolism. When this happens, the brain’s central clock remains on schedule. This can result in a de-synchronization between the two. "That then could lead to abnormal weight gain or a decrease in weight loss," Scheer says.
Part of this could be due to the body’s ability to handle glucose. Late eaters in the study showed significantly higher HOMA levels, an index of insulin resistance that’s used to identify diabetes.
The body’s system is better able to cope with higher glucose levels in the morning, Scheer says, extracting sugar from the blood to use as energy. "The same meal load later in the day would not be received as well."
The late eaters in the study often ate less for breakfast or skipped breakfast all together. Past studies have shown that’s a recipe for diet disaster. Fasting for too long can put the body into so-called "storage mode." People who skip breakfast are also more likely to overeat later, although the study authors did not find a significant difference in the overall calories both groups ate.
"We should really seriously consider the effect of not only what we eat, but when we eat," Scheer says.
International Journal of Obesity Jan. 23, 2013