Adverse effects of consuming high fat-sugar diets on cognition: implications for understanding obesity

There is increasing evidence for important roles of key cognitive processes, including attention, memory and learning, in the short-term decision making around eating. There is parallel evidence that people who are overweight or obese tend to perform worse on a variety of cognitive tasks. In this review, the evidence for these two ideas is summarised and then the idea that overconsumption of Western-style high-fat high-sugar diets may underlie the association between obesity and poorer cognitive performance is explored. In particular, evidence in animals and humans that repeated consumption of high fat or high fat and sugar diets leads to specific impairments in the functioning of the hippocampus which underpin the consequent changes in cognition is summarised. These findings lead into the vicious cycle model, which suggests that these cognitive changes have knock-on negative effects for future appetite control, and evidence that altered hippocampal function is also associated with impaired appetite control is explored. The review concludes that there is consistent evidence in the animal literature and emerging evidence from human studies that supports this vicious cycle model. It is also noted, however, that to date studies lack the nutritional specificity needed to be able to translate these basic research findings into clear nutritional effects, and concludes that there is an urgent need for additional research to clarify the precise nature of the apparent effects of consuming high fat and sugar diets on cognition.