Interventions involving a major dietary component improve cognitive function in cognitively healthy adults: a systematic review and meta-analysis.

Accumulating evidence suggests a role for diet in promoting brain health. The purpose of this systematic review was to (i) quantitatively assess whether interventions with a major dietary component can enhance cognition in cognitively healthy adults, and, (ii) identify responsive domains of cognition to inform the design of future dietary trials. Electronic databases were systematically searched to find eligible randomized controlled trials that assessed the effect of interventions with a major dietary component on cognitive function or incident dementia, in adults without known cognitive impairment. Standardized mean differences (SMD) (95% confidence Interval [CI]) were combined using a random-effects meta-analysis and tests of homogeneity of variance were calculated. Two trials reported dementia outcomes and were qualitatively described. Fifteen trials encompassing 6,480 participants were eligible for meta-analysis. Compared to control, intervention improved performance on measures of global cognition (SMD=0.14; 95% CI 0.01 to 0.27, P=0.05; I2 76%), executive function (SMD=0.11; 95% CI 0.04 to 0.18, P=0.003; I2 0%) and processing speed (SMD=0.12; 95% CI 0.05 to 0.19, P=0.001; I2 0%). There was no effect of intervention on delayed memory (SMD=0.04; 95% CI -0.02 to 0.09, P=0.18; I2 4%). Significant heterogeneity and funnel plot asymmetry were detected for global cognition but removal of studies with high risk of bias did not change the pooled findings. Current evidence is limited but indicates that diverse interventions improve non-memory cognitive functions during normal cognitive aging. Measures of executive function and processing speed should be considered as feasible end-points in future dietary intervention trials.