ABSTRACT
The brain relies on carbohydrates, and in particular glucose, as its main energy source, which is indeed essential for its functioning (Amiel 1994). Difficult tasks requiring intensive cognitive resources have been shown to result in a measurable decline in peripheral blood glucose concentration in human studies suggested to be due to increased neural energy expenditure (Reivich and Alavi 1983; Donohoe and Benton 1999; Scholey et al. 2006). In animals, it has been shown that at a high cognitive load, the glucose demand of the hippocampus exceeds supply, whereas exogenous glucose supply enhances performance (McNay et al. 2000). This is also supported by a number of human studies that have shown that glucose consumption compared to placebo or breakfast omission enhances cognitive performance both in healthy participants and in participants with memory deficits and those with poor glucose regulation (Smith et al. 1994; Korol and Gold 1998).
9.1 Introduction .......................................................................................................................... 173 9.1.1 The Role of Carbohydrates in Cognitive Function (CF) .......................................... 173 9.1.2 Domains of CF Assessed .......................................................................................... 174 9.1.3 Assessment of CF ..................................................................................................... 175
9.2 Diet GI or GL and Cognition ................................................................................................ 175 9.2.1 Characteristics of Studies Assessing the Effect of Dietary GI on CF ...................... 188 9.2.2 Characteristics of Studies Assessing the Effect of Dietary GL on CF ..................... 188 9.2.3 Meal Interventions .................................................................................................... 188 9.2.4 Assessment of CF ..................................................................................................... 188 9.2.5 Findings of Studies Assessing GI and Cognition in Children .................................. 189 9.2.6 Findings of Studies Assessing GI and Cognition in Adults ..................................... 189 9.2.7 Findings of Studies Assessing GL and Cognition in Children ................................. 190 9.2.8 Findings of Studies Assessing GL and Cognition in Adults .................................... 190
9.3 Summary of Findings of Studies Assessing the Effect of GI/GL on CF ............................. 191 9.4 Contrasting Outcomes .......................................................................................................... 192 9.5 Possible Mechanisms Explaining the Effect of Diet GI on Cognitive Function .................. 193 9.6 Recommendations for Future Research and Research Design ............................................. 195 9.7 Conclusion and Suggested Clinical Practice ........................................................................ 196 References ...................................................................................................................................... 196
The optimal glucose dose for enhancing verbal episodic memory, relative to placebo in elderly participants, was found to be 25 g, or a blood glucose concentration of approximately 8-10 mmol/L (144-180 mg/dL) (Parsons and Gold 1992), whereas in healthy young women, the optimal glucose dosage was found to be 300 mg/kg body weight (Messier et al. 1998).
