Breakfast serves many functions. It increases focus, reduces the risk of heart disease in men, and potentially impacts your appetite throughout the day.

Cell Metabolism recently published a study that found that eating more calories earlier does not impact how calories are used. However, eating a higher intake of calories earlier in the day may lead to a reduced appetite later in the day.  Lead author Professor Alexandra Johnstone, a researcher in the field of appetite control at the Rowett Institute at The University of Aberdeen, Scotland, stated that the myths around meal timing and how it impacts body weight and health have been spearheaded by the circadian rhythm field.

Nutrition experts have asked, “Where would the energy go?” To answer this question, the researchers “decided to take a closer look at how time of day interacts with metabolism." The small study of overweight or obese subjects (16 men and 14 women) agreed to have their metabolisms checked and their diets controlled over a certain period. Subjects were randomly assigned to eat either a large meal at breakfast (morning-loaded) or a large meal at dinner (evening-loaded) for four weeks. The diets were equal in calories and included 30% protein, 35% carbohydrates, and 35% fat. Following a one-week washout period, where calories were spread throughout the day, the participants transitioned to either the morning-loaded or evening-loaded diet for four weeks. This way, each subject was its study control.

The participants’ total daily calorie expenditures were checked using a doubly labeled water method. The method is isotope-based and evaluates the difference in oxygen and hydrogen turnover rates in body water as a function of carbon dioxide production. The study's main endpoint was tracking changes in body weight based on diet type. The researchers discovered that energy expenditure and total weight loss were equal in morning-loaded and evening-loaded diets. Subjects lost roughly seven pounds during the four-week study.

Additional endpoints monitored during the study included appetite control, glycemic control, and body composition. "The participants reported that their appetites were better controlled on the days they ate a bigger breakfast and that they felt satiated throughout the rest of the day,” Johnstone says. “This could be quite useful in the real-world environment, versus the research setting in which we were working.” There were a few limitations to the study, however. The study was done under free-living conditions and not in a lab. Additionally, certain metabolic measurements were available after the morning meal but not after the evening meal.

Lead author Johnstone advised that this study could look at intermittent fasting (aka time-restricted eating) to help identify the best time of day for people to eat when following this diet. Johnstone’s group plans to advance the research by studying how time-of-day impacts metabolism in participants who do shift work. It’s plausible that these workers have different metabolic reactions to the disturbance of their circadian rhythms. "One important thing to note is that when it comes to timing and dieting, there is not likely going to be one diet that fits all," Johnstone concludes. "Figuring this out is going to be the future of diet studies, but it's very difficult to measure."Want to learn how to implement these findings with your clients? Don't miss Skipping Breakfast But Still Looking to Lose Weight? Here are Some Tips...

By Lisa Andrews, MEd, RD, LD

References:

1. St-Onge, A. J., Baskin, M. L., Johnson, H. M., Chiuve, S. E., Kris-Etherton, P., & Varady, K. (2017). Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation, 135(9), 96–121. https://doi.org/10.1161

2. Ruddick-Collins, L. C., Morgan, P. J., Fyfe, C. L., Filipe, J. A. N., Horgan, G. W., Westerterp, K. R., Johnston, J. D., & Johnstone, A. M. (2022). Timing of daily calorie loading affects appetite and hunger responses without changes in energy metabolism in healthy subjects with obesity. Cell Metabolism, 34(10). https://doi.org/10.1016/j.cmet.2022.08.001