Cognitive function may be affected by long-term diet and most of the support for this idea is derived from human correlational studies and animal prescribed diet studies. To date there has been no systematic examination of human experimental studies that examine whether a prescribed long-term (24 h+) diet can cause changes in cognitive function. Here, we review the experimental evidence of long-term changes in cognition following prescribed diet interventions. A total of 30 diet interventions were identified and reviewed. Measures of working memory, long-term memory, and attention appeared most sensitive to dietary manipulation, but there was considerable variability in outcome. Additionally, energy and fat intake manipulations tended to influence performance on these measures to the greatest degree. This review also serves to identify factors that should be considered in designing future diet-cognition studies. We also suggest a series of cognitive tests based on this review and indicate potentially profitable directions to take the diet-cognition literature.