Breakfast is literally named because it breaks the overnight fast. In this regard, it has very important metabolic implications. During the night, as fasting proceeds, an increasing catabolic state is entered whereby stored tissues are catabolised and then oxidised to maintain the energy requirements of the cells. Glycogen is broken down from the liver and used to maintain adequate blood sugar, and this is used largely by the brain. Fat is also oxidised as a general source of energy, and this occurs through the release of fatty acids to the circulation, mainly from adipose tissue. Protein is also broken down from skeletal muscle, and the resulting amino acids are transported to the liver where they are deaminated and the carbon skeletons converted to glucose, or ketones, the former contributing to blood sugar levels, the latter being oxidised for their energy. This catabolic process is a necessary and normal process, but cannot be maintained indefinitely without serious health repercussions.
Breakfast is the meal that shift this catabolic state back to a mainly anabolic one, and in this regard is vital metabolically. Evidence suggests that those who skip breakfast are less healthy and often possess more body weight. The association between skipping breakfast and gaining weight is fairly well established, but it is less certain if breakfast is causal in these effects. However, some evidence suggests that a causal relationship between these parameters does exist. For example, in one study1, researchers investigated the physical activity levels and the eating habits of breakfast consumers and non-breakfast consumers using a randomised controlled trial. Subjects aged 21 to 60 years were randomly allocated to receive a daily breakfast (700 kcal before 1100 or 0 kcal until 1200) and then their activity and eating habits were monitored. The main finding of the study was that breakfast consumption resulted in increases in the thermic effect of activity (TEA). However, over 24 hours the TEA was not different between groups.
In addition, the results showed that 24 hour energy consumption was not different between the two groups, despite one consuming breakfast, while the other fasted. This indicates that the non-breakfast consumers consumed a greater amount of energy during the subsequent parts of the day. Those that skip breakfast in the belief that they are reducing their energy intake may therefore be misguided. The researchers also showed that in the subjects the body mass of the subjects increased over time, suggesting that both groups were getting fatter. This was subsequently confirmed through use of body composition analysis, which showed no treatment effect on body composition. The implication of this is that all of the subjects were getting fatter, and this suggests that the food and lifestyle they were leading were unhealthy. This highlights an important component of much Western research, in that nearly always the study population are unhealthy to begin with. This study may be interesting to repeat in those with a high quality diet.
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