Many people are unknowingly fasting because they do not eat from early evening one day to lunch time the following day. Evidence suggests that skipping breakfast is associated with certain detrimental health outcomes including weight gain and obesity. However, detrimental effects to cognitive function may also be a side effect of fasting. One of the effects of fasting is a reduction in the blood sugar levels, particularly as glycogen supplies in the liver become depleted. This reduction in the availability of glucose changes the insulin to glucagon ratio and this causes a metabolic shift to alternative fuel utilisation, particularly glucogenic amino acids. As glycogen supplies become depleted and glucose availability diminishes, the use of amino acids from muscle tissue for conversion to glucose (the alanine cycle) in the gluconeogenic pathway proceeds at an accelerated rate. However, the glucose produced from such a pathway not be optimal to supply the brain with required levels of fuel.
Glucose is the primary fuel used by the brain for metabolic activity and low blood sugar levels are associated with poor mental performance. As the brain accounts for up to 50 % of the glucose utilisation in children, it could be expected that the detrimental effects of skipping breakfast may be particularly apparent in children. Further, the normal gluconeogenic upregulation that occurs in adults is also limited in children because of their low levels of skeletal muscle. Because of this, researchers have investigated the effects of overnight fasting on the cognitive ability of school children between the ages of 9 to 11 years1. The results from this study showed that fasting had detrimental effects on the ability to problem solve by reducing the accuracy of the responses. However, the children appeared to have improved immediate recall. The authors put this down to increases in the arousal levels of the children by activation of the sympathetic nervous system caused by the metabolic stress of fasting.
When the authors tested the blood glucose levels of the children they found no difference between those who had breakfast and those who skipped breakfast. However, the authors did find statistically higher levels of lactate, fatty acids and the ketone β-hydroxybutyrate in fasted children. This the authors suggested was evidence of metabolic stress, and is consistent with raised levels of adrenal corticosteroids and catecholamines, the latter of which may have been responsible for the improvements in cognition. It is not surprising that missing breakfast causes deterioration is some mental faculties because fasting may limit the plasma glucose levels to the lower end of the normal homeostatic range. Good nutrition is required for health and clear mental thinking is part of being healthy. Eating a high quality breakfast containing whole animal protein and whole grain carbohydrates or whole fruit is an important consideration for those who wish to maintain blood glucose levels throughout the day.
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