Front-loading calories in morning reduces hunger but does not affect weight loss

There's the old saying in dieting that one must "breakfast like a king, lunch like a prince, and dine like a pauper," based on the belief that consuming the bulk of daily calories in the morning optimizes weight loss by burning calories more efficiently and quickly. But according to a new study published in Cell Metabolism, whether a person eats their largest meal early or late in the day does not affect the way their body metabolizes calories. However, people who ate their largest meal in the morning did report feeling less hungry later in the day, which could foster easier weight loss in the real world.

In this study, the investigators recruited healthy subjects who were overweight or obese to have their diets controlled and their metabolisms measured over a period of time; 16 men and 14 women completed the study. Each participant was randomly assigned to eat either a morning-loaded or an evening-loaded diet for four weeks. The diets were is caloric, with a balance of 30% protein, 35% carbohydrate, and 35% fat. After a washout period of one week in which calories were balanced throughout the day, each participant crossed over to the opposite diet for four weeks. In that way, each participant acted as their own study control.

Throughout the study, the subjects' total daily energy expenditures were measured using the doubly labelled water method, an isotope-based technique that looks at the difference between the turnover rates of the hydrogen and oxygen of body water as a function of carbon dioxide production. The primary endpoint of the study was energy balance measured by body weight.

Overall, the researchers found that energy expenditures and total weight loss were the same for the morning-loaded and evening-loaded diets. The subjects lost an average of just over 3 kg (about 7 pounds) during each of the four-week periods.

Ref:

Professor Alexandra Johnstone et al,Timing of daily calorie loading affects appetite and hunger responses without changes in energy metabolism in healthy subjects with obesity, Cell Metabolism, DOI: 10.1016/j.cmet.2022.08.001