The role of breakfast is the subject of controversial discussion within the framework of the examination of the daily energy intake. There are both results pointing out that the energy intake after a substantial breakfast over the entire day is less, and a range of other studies that suggest that a high energy consumption at breakfast is not compensated during the day and hence contributes to a higher calorie intake overall.

In order to examine these contradictions more closely, the authors analysed the data on the energy consumption of 100 normal and 280 overweight individuals during meals over ten or 14 days. In the process, the intra-individual energy intake during breakfast and the ratio of breakfast calories to the overall energy intake during the day were calculated. 280 overweight individuals (of whom, 205 female, 75 male, average age 45 +/- 0.85 years, BMI 36.6 +/- 0.2 kg/m2), who had sought help in overcoming their weight problems at the Clinic for Nutritional Medicine in Munich, were selected for the study. They were compared with a group of 100 volunteers, who corresponded with the patients as closely as possible (67 female, 33 male, age 42 +/- 0.2 years, BMI 22.5 +/- 0.1 kg/m2). 

Prior to commencing treatment, all individuals were asked to diarise all foodstuffs and beverages consumed. In order to motivate particularly the overweight individuals to make correct statements, they were told that they should continue their normal diet as usual and that an exact record of their dietary habits was of great importance for the success of the treatment to follow. In order also to ensure a record of high-energy food and between-meal snacks, it was also pointed out that personally preferred foodstuffs are retained in the diet whenever possible during the following treatment. The subjects were urged to use a scale whenever possible for the quantity information for the meals and they were given a brochure to help with estimating portion sizes. The normal weight subjects were to log their meals over 14 days; the overweight patients, over ten days.

The amounts of energy consumed were calculated using the subjects’ information and main meals and between-meal snacks were collated. Calorific beverages were recorded separately. The data for each participant were sorted in an ascending ranking according to the amount of energy taken in at breakfast. Both groups were compared with the aid of paired t-tests, with multiple testing using Bonferroni correction. Correlations between the energy intake during the day and the breakfast meal were determined according to Pearson, and the impact of the energy content of breakfast on the calories taken in over the whole day was investigated using multiple regression analyses. The energy content of breakfast for the overweight individuals was between 121 +/- 7.1 and 606 +/- 19.0 kcal. This wide distribution arose due to accidentally missed meals. Regardless of the amount of calories of breakfast, midday and evening meals each contained approximately 550 kcal. Between-meal snacks in the morning were significantly smaller with a substantial breakfast, while between-meal snacks during the afternoon and the evening were not influenced by this. On both days when the breakfast in the morning was the largest, the amount of energy taken in over the day was approximately 400 kcal higher than otherwise, which was essentially conditioned by the amount of calories in the breakfast. Including the beverages containing calories, a general increase in the amount of energy taken in was observable, which was in parallel with the energy intake during the whole day, such that the statements made previously remained unchanged. The proportion of all other meals of the amount of energy taken in per day overall decreased consistently as breakfasts became more substantial. For normal weight individuals, the calories consumed at breakfast were between 134 +/- 12.8 and 674 +/- 24.6 kcal. Even here, the meal was occasionally omitted. Midday and evening meals contained a relatively constant 500 to 550 kcal. 

Just as for the overweight participants in the study, the proportion of all other meals of the amount of energy taken in per day overall decreased in relation to a breakfast becoming more substantial. Even in this group, the results did not change when beverages containing calories were included. The main ingredients responsible for the clearly higher energy intake at breakfast were bread, eggs, cakes, yoghurt, cheese, sausage products, jam and butter.
In both groups, the energy intake at breakfast correlated positively with the amount of energy taken in over the whole day. Multiple regression analyses confirmed that the amount of energy taken in at breakfast in both groups, as well as its proportion relative to the daily calorie intake, had an impact on the calories consumed over the whole day. While, therefore, the other meals of the day continued to remain constant, viewed over the whole day, a larger breakfast resulted in a proportionally increased intake of calories. Hence, in order to prevent or to treat overweight, a reduction in breakfast calories could be helpful, since, according to this study, a higher energy consumption at breakfast is not adequately compensated over the day.