Carbohydrates, glucose and cognitive performance

Glucose, a monosaccharide carbohydrate, is the brain’s primary fuel. As such, numerous research investigations over the past 20 years have sought to determine the influence of acute glucose ingestion on human cognitive performance. Initial work focused on older adults and individuals with age-related memory impairment. The majority of studies in this age group have reported a beneficial effect of oral glucose on performance, most notably in the domain of episodic memory. More recently, this effect has been replicated in younger adults and adolescents. However, in younger individuals, the ‘glucose memory facilitation effect’ appears to be more sensitive to conditions of high cognitive demand. By contrast, numerous studies in children have reported that meals delivering a relatively lower glycaemic load are associated with greater cognitive enhancement than ingestion of a high glycaemic load. This is likely to be best explained by the lower glycaemic load delivering a more prolonged release of glucose into the bloodstream during the hours after food ingestion, which may result in enhanced capacity for attention during this period. These findings have implications for dietary recommendations pertaining to the types of foods that children should be consuming at breakfast and lunch, before attending school classes. In addition, long-term studies which have focused on carbohydrate withdrawal (i.e. in the case of low carbohydrate weight loss diets) have found a detrimental effect of reduced long-term carbohydrate intake on cognitive functioning. Finally, other carbohydrates including sucrose (also known as table sugar, and which is synthesised from glucose) and fructose, and their respective effects on cognitive performance, will be considered. In summary, the findings in this area suggest that both acute and long-term carbohydrate intake play a role in mediating cognitive performance. Further, previous research implies that subtly different effects of carbohydrates on performance may be observed during different stages of the lifespan.