乌鸦传媒

The body uses more than twice as much energy to digest breakfast than dinner, a finding that emphasizes the importance of breakfast for weight loss, scientists said.

In 16 volunteers who spent 3 days in a lab under carefully monitored conditions, diet-induced thermogenesis (DIT) was 2.5 times higher in the morning after breakfast than in the evening after dinner (P<0.001), regardless of how large the meal was, Juliane Richter, PhD, of the University of Lübeck in Germany, and co-authors reported.

Furthermore, study participants who ate a low-calorie breakfast reported increased feelings of hunger (P<0.001) and specifically cravings for sweets (P=0.007) later in the day, compared with participants who ate a high-calorie breakfast.

"Our data show that the time of day of food intake makes a difference in humans' energy expenditure and metabolic responses to meals," the team wrote online in the . "These in-laboratory standardized experiments, which eliminated the possible influence of sleep disturbances and carbohydrate preloads, support the thesis that in terms of DIT, breakfast has a more efficient energetic value for our body than dinner."

"Moreover," the researchers added, "our study expanded this knowledge by the insight that diurnal variations in DIT persist on hypocaloric meals. Thereby, our findings may contribute to elucidate a research issue that has been intensely discussed for years."

Previous studies exploring this issue have reported mixed results, but these studies lacked standardized laboratory conditions, and their measurements may have been affected by the influence of physical activity, Richter and co-authors explained.

Their new randomized crossover study included 16 healthy, normal-weight male volunteers (mean age of 23.6, mean body mass index of 22.5). During 3 days spent in a lab, participants consumed a predetermined low-calorie breakfast (11% of individual daily calorie requirement) and a high-calorie dinner (69%) in one condition and vice versa in the other.

Under blinded conditions, the researchers measured DIT by indirect calorimetry. Parameters of glucose metabolism were also measured, and participants' hunger and appetite for sweets were rated on a visual analog scale.

The researchers reported that food-induced increases in blood glucose and insulin were higher after dinner compared with breakfast. For example, glucose concentrations were 17% higher after a low-calorie dinner compared with a low-calorie breakfast (P<0.001), and insulin concentrations were 40% higher after a high-calorie dinner compared with a high-calorie breakfast (P=0.001).

Asked for her perspective, Lauri Wright, PhD, of the University of North Florida in Jacksonville, who was not involved with the study, said the research provides new information about the first meal of the day: "We have long known that eating breakfast is important for health. Benefits include a healthier weight, keeping blood sugar steady, better concentration at school and work, and even heart health. This new study, though, shows that our body is 'rev-ed' up in the morning and has a better metabolic response to breakfast than other times of the day," she told 乌鸦传媒 via email.

The study lends no support to the concept of intermittent fasting, a popular dietary practice that has received much attention lately, Wright added. "The study results actually contradict intermittent fasting. Translating this study's findings, the optimal pattern for health is a larger breakfast and a small dinner."

A chief limitation of the study, Richter and co-authors said, was that the participants were all men, which had been done to avoid possible effects of the female hormone cycle on energy metabolism. Another limitation was a lack of analysis of the biological mechanisms underlying the results. "The underlying mechanisms of appetite regulation, hypothalamus–pituitary–adrenal axis activity, glucose metabolism, and postprandial energy turnover cannot be identified by our study because of the human experimental approach," the team wrote.

"Overall, the diurnal variations in DIT, independent of the calorie content of the meals, imply that the time of food intake is important not only in the prevention of obesity but also in terms of diets for weight loss," the researchers concluded. "An extensive breakfast should therefore be preferred over large dinner meals to reduce the risk of metabolic diseases."

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