It is widely acknowledged that the quality of nutrition affects many aspects of physical and mental performance. A vegan diet is associated with superior cardiovascular and cerebrovascular conditions. Mediterranean diets (high fruit and vegetable content) are linked with reduced risk of neurodegenerative diseases and improved performance on cognitive tests. In the present study, verbal memory and sleep quality were assessed in a cohort of 62 adults aged 40 and above. Using a modified Mediterranean Diet Adherence Screener, the participants were divided into the categories of vegan, vegetarian, pescatarian, omnivores with low meat/fish consumption, and omnivores with high meat/fish consumption. The California Verbal Learning Test was used to assess verbal learning memory, and the Pittsburg Sleep Quality Index was used to assess sleep quality. Diet was found to have a significant effect on memory but no significant effect on sleep quality. The sample size may have been insufficient to capture the effects of diet on sleep. To definitively establish the relationships between diet patterns and quality of cognitive functioning and sleep, further research is required. The results of this study cast doubt on the hypothesis that the consumption of animal products boosts memory performance.