The Impact of Glycemic Load on Cognitive Performance in Adults: A Systematic Review and Meta-Analysis

Abstract

Objectives A systematic review and meta-analysis compared the effects of high (HGL) and low glycemic load (LGL) breakfasts on the cognitive performance of adults. In particular, the time after eating that cognition was assessed and the influence of pre-existing glucose tolerance (GT) were considered. Methods A systematic search for randomized and non-randomized acute breakfast studies was conducted using PubMed, Scopus, and Cochrane Library. Data were available from 15 studies (1,100 participants, age 20–80 years). Episodic memory (e.g., word list recall), working memory (e.g., Serial Sevens), and attention/vigilance (e.g., Trails Part A) were examined. Better and poorer GT were defined as fasting glucose < or > 6.1 mmol/L (110 mg/dL) and/or two-hour postprandial glucose < or > 7 mmol/L (126 mg/dL). All analyses were performed using RevMan 5.3 (Cochrane) and a random-effects model. Results Five to 110 minutes after eating a HGL or LGL breakfast there were no differences cognition. However, between 120 and 195 minutes, immediate episodic memory was significantly better following a LGL breakfast (SMD = 0.16, 95% confidence interval [CI] = –0.00–0.32, P = 0.05, I2 = 0%). Pre-existing glucose tolerance (GT) status moderated this effect. In those with better GT, immediate episodic memory was significantly better following a LGL breakfast (SMD = 0.26, 95% CI = 0.00–0.52, P = 0.05, I2 = 0%), whereas there was no difference in those with poorer GT (SMD = 0.12, 95% CI = –0.21–0.45, P = 0.47, I2 = 0%). Conclusions A LGL breakfast improved memory later in the morning, especially in those with better GT. The phenomenon is unlikely to occur in pre-diabetics or type 2 diabetics and as such there are no clinical implications. There is, however, a possibility of exploring the nature of breakfast, or developing functional foods, to improve memory and work performance. If a similar phenomenon was found in children, there could be positive consequences for school performance. Funding Sources This study was not funded.