Does habitual caffeine consumption moderate the association between a high fat and sugar diet and self-reported and episodic memory impairment in humans?

With an increasing number of studies reporting the association between a high fat and sugar (HFS) diet and impaired memory, a need to investigate strategies to mitigate this effect is crucial. Caffeine's impact on cognition has been widely studied, with recent reviews discussing possible neuroprotective properties. Additionally, animal studies have shown caffeine may protect against HFS diet-induced memory impairment. However, human research remains limited. This study investigated whether caffeine consumption moderates the association between a HFS diet with both self-reported (measured in Experiment 1 and 2) and episodic (measured in Experiment 2) memory impairment. Experiment 1 recruited 1000 (263 males, 726 females, 11 declined to say) healthy volunteers aged 18 - 45, who completed the Dietary Fat and free Sugar (DFS) questionnaire and Everyday Memory Questionnaire (EMQ) (a self-report memory measure) along with self-reporting daily caffeine consumption (mg). In Experiment 1, the moderation effect of caffeine on DFS and EMQ approached significance when controlling for age and sex (β = -0.090, p = 0.056). However, caffeine did moderate the relationship between the DFS fat subscale with EMQ even when controlling for age and sex (β = -0.099, p = 0.026). Experiment 2 recruited 699 (98 males, 594 females, 7 declined to say) healthy volunteers aged 18-45, who again completed the DFS, EMQ and self-reported caffeine consumption, as well as a Verbal Paired Associates (VPA) task (an episodic memory measure). Caffeine consumption did not significantly moderate the relationship between the DFS including its subscales with either memory measure. These findings suggest that caffeine consumption is unlikely to protect against the impact of a HFS diet on memory impairment. However, future research is required to validate this finding and to better understand the neurobiological mechanisms underpinning this relationship.