There is increasing evidence for important roles of key cognitive processes, 
including attention, memory and learning, in the short-term decision making 
about 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 (HF)-high-sugar diets may underlie the 
association between obesity and poorer cognitive performance is explored. In 
particular, evidence in animals and human subjects that repeated consumption of 
HF or HF and sugar (HFS) 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 (VCM), 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 VCM. 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 HFS diets on cognition.