The Mediterranean diet has been touted for decades as one of the best diets for both health and fitness, but this secret to the enviable European figure may lie in when you eat, not what you eat, according to a new study.
The study, published in the International Journal of Obesity, was conducted by researchers from Boston’s Brigham and Women’s Hospital (BWH) and Tufts University in conjunction with researchers at the University of Murcia in Spain.
Data on 420 overweight and obese participants in a 20-week weight loss program in Spain was gathered and analyzed. Participants attended group therapy sessions, received nutrition and exercise counseling, and recorded both physical activity and daily caloric intake.
Participants were on the “Mediterranean diet,” where the main meal, which accounts for about 40% of daily calories, is lunch. They were divided into two groups by the timing of this meal. Early-eaters were those who ate lunch before 3 P.M., and late-eaters were those who had lunch after 3 P.M.
At the end of the 20 weeks, weight loss results were compared between the two groups, and researchers found that the early-eaters lost more weight more rapidly than the late-eaters, despite having similar caloric intake and physical activity levels.
Early-eaters lost an average of 22 lbs., about 11% of their starting weight, while late-eaters lost an average of 17 lbs., about 9% of their starting weight.
The timing of other meals did not seem to have an effect on weight loss success. Researchers did find, however, that late-eaters were more likely to skip breakfast and consumed fewer calories when they did eat breakfast. Late-eaters also had lower insulin sensitivity, a risk factor for diabetes.
While researchers could not pinpoint a singular reason for the greater weight loss in the early-eaters, they did provide a few hypotheses.
One theory is that glucose, or sugar, is processed differently by the body depending on the time of day. Your body is better able to cope with higher glucose levels in the morning, using sugar in the blood to provide energy after the long, nightly fast.
Another theory is that the timing of meals affects the circadian system – the body’s cellular clocks, which are controlled by a group of cells in the hypothalamus (in the brain). Studies have found that feeding animals during abnormal times can “reset” the clocks in the liver and pancreas. This de-synchronization could affect metabolism, leading to abnormal weight gain or a decrease in weight loss.
And a third theory focuses on a possible genetic link. Researchers have identified several genes, including the “CLOCK” gene that may impact obesity and sleep cycles. One variant of the gene, known as the “c” allele, has been linked to obesity, and it was found to be more common in the study’s late-eaters.
Dr. Frank Scheer, senior study author, director of the Medical Chronobiology Program and associate neuroscientist at BWH states,"[While] we cannot directly translate these findings to Americans, we would expect that a later dinner -- the main meal for most Americans -- might similarly impair weight loss.”
The Bottom Line
It’s not surprising that late-eaters, who tended not to eat breakfast, had less success losing weight, as research shows that successful dieters eat breakfast.
And while the study focuses on the timing of meals rather than the composition, it is worth noting that the Mediterranean diet is drastically different from the typical American diet. It consists mainly of unprocessed plant-based foods – vegetables, fruits, legumes, whole grains, nuts, and olives – supplemented with some cheese, yogurt, fish, poultry and eggs. Red meat consumption is limited, as are fried foods, sodium, and sweets, and healthy fats such as olive oil are used in place of butter.
It’s clear that there is much we do not understand about obesity and its causes, but managing food and caloric intake is crucial to getting weight under control. Based on this latest study, the advice “Eat breakfast like a king, lunch like a prince, and dinner like a pauper” seems to ring true.