Regulation of energy intake depends in part on both memory for prior food intake and internal signals of hunger and satiety. These functions are both mediated by the hippocampus, a brain structure that animal studies have shown to be impaired after maintenance on high fat and refined sugar (HFS) diets. Study 1, using a cross-sectional design, revealed that self-reported HFS diet was associated with poorer performance on hippocampal sensitive memory tasks but not other neuropsychological control measures. Study 2 replicated this finding in two groups selected to differ in HFS intake, additionally showing that this effect is specific to hippocampal functioning and does not extend to measures of prefrontal cortex function. Furthermore, in a laboratory-based test of food intake, the HFS rich diet groups were less accurate in recalling what they had previously eaten and evidenced reduced sensitivity to internal signals of hunger and satiety, relative to a group consuming less HFS rich diets. Together, these findings reveal an association between HFS consumption and poorer hippocampal function in human participants, consistent with findings from animal-based studies. Moreover, our results suggest that this may be related to impaired regulation of energy intake via less accurate tracking of prior food intake and reduced sensitivity to hunger and satiety signals.