Breakfast is a critical meal because it influences practically every dimension of our being during the course of the day, including how we perform physically and mentally. Breakfast immediately raises the body’s energy level and restores the blood glucose level to normal after an overnight fast. It also raises the muscle and liver glycogen stores. Carbohydrate is the preferred fuel for muscle and the nervous system (2, 3). Low carbohydrate levels result in poor performance and rapid fatigue during training and other physical activities (4, 5). Perceived exertion is also elevated when blood glucose and muscle glycogen levels are low making exercise mentally challenging (5, 6). Therefore, starting a training session with low carbohydrate availability can significantly limit the quality of one’s training session and adversely impact training adaptation. A well-designed breakfast can provide an adequate amount of carbohydrate and other essential nutrients to raise the blood glucose levels and get a morning training session going with vigor and vitality, and without being overly filling.
Second, breakfast immediately lowers the blood level of the stress hormone cortisol, which peaks during the early morning hours (7, 8). We generally think of sleep as a non-stressful period. From a psychological viewpoint this is generally true. Physiologically, however, it is quite the opposite. Even though our metabolic needs decrease significantly while we are sleeping, the body still needs to maintain critical physiological and metabolic functions required to support life as well as those which foster daily recovery, tissue repair and growth and development – key components to training adaptation. The energy to support these functions come from blood glucose, liver glycogen and free fatty acids.