Front-loading calories early in the day reduce hunger but do not affect weight loss.
In the diet, there is a saying that one should “breakfast like a king, lunch like a prince, and dinner like a pauper.” It is based on the belief that consuming the bulk of your daily calories in the morning improves weight loss by burning calories more efficiently and quickly. However, according to a new study published September 9 in the journal cell metabolismHowever, the way the body metabolizes calories is not affected by whether it eats its largest meal early or late in the day. On the other hand, the study found that people who ate the largest meal in the morning reported feeling less hungry later in the day, which may promote easier weight loss in the real world.
“There are a lot of myths about the timing of eating and how it can affect body weight or health,” says lead researcher Professor Alexandra Johnston. She is an appetite control researcher at the Rott Institute at the University of Aberdeen in Scotland. “This was largely driven by the field of circadian rhythms. But in the field of nutrition we wondered how this might be possible. Where does the energy go? We decided to take a closer look at how the time of day interacts with metabolism.”
In this study, researchers recruited healthy people who were overweight or obese to control their diets and measure their metabolism over a period of time. There were 16 men and 14 women who completed the study. Each participant was randomly assigned to eat either a loaded diet in the morning or a loaded diet in the evening for four weeks. The diets were isocaloric (containing the same number of calories), with a balance of 30% protein, 35% carbohydrates, and 35% fat. Each participant then switched to the opposite diet for four weeks, after an average break of one week in which calories were balanced throughout the day. Using this method, each participant served as his or her own study control.
Throughout the study, the subjects’ total daily energy expenditure was measured using the double-described water method. This is an isotope-based technique that investigates the difference between hydrogen and oxygen turnover rates in body water as a function of carbon dioxide production. The primary end point of the study was energy balance measured by body weight. In general, the investigators found that energy expenditure and overall weight loss were the same for the morning and evening loaded diets. Participants lost just over 3 kg (about 7 pounds) during each of the four-week periods.
Secondary end points were subjective control of appetite, glycemic control, and body composition. “Participants reported that their appetite was better controlled on the days when they ate a larger breakfast and that they felt fuller throughout the day,” Johnston says. “This could be very useful in the real world environment, versus the research environment we’ve been working in.”
One limitation of the research is that it was conducted under free-living conditions and not in a laboratory. In addition, some metabolic measurements were only available after breakfast and not after dinner.
Johnston notes that this type of experiment could be applied to a study of intermittent fasting (also called time-restricted eating), to help determine the best time of day for people on this type of diet to consume calories.
In the future, the group plans to expand its research into how the time of day affects metabolism by conducting studies similar to those described here on people who do shifts. Because their circadian rhythms are disturbed, it is possible for these individuals to have different metabolic responses. “It is important to note that when it comes to timing and dieting, it is unlikely that there is a one-size-fits-all diet,” Johnston concludes. “Discovering this will be the future of diet studies, but it is very difficult to measure.”
Reference: “Timing of daily calorie loading influences appetite and responses to hunger without changes in energy metabolism in healthy, obese subjects” by Leonie C. Roddick Collins, Peter J. Morgan, Claire L. Fife, Joao Ann Philippe, Graham W. Horgan, Claes R. Westertrip, Jonathan D. Johnston and Alexandra M. Johnston, 9 Sep 2022, Available here. cell metabolism.
This study was funded by the Medical Research Council, the Scottish Government and the Department of Analytical Services, Rural and Environmental Sciences.