Obesity is one of our most serious health concerns and emerging data shows impacts of mid-life obesity on future cognitive decline. Our research in rodents models the western lifestyle, focussing on how provision of a varied, energy rich diet can override the control mechanisms that should maintain body weight. Using supermarket foods high in fat and sugar, we showed that a high choice ‘western’ diet high in fat and sugar leads to changes in neurotransmitters involved in the hedonic appraisal of palatable foods. Furthermore, access to this palatable diet attenuated the physiological effects of acute stress (restraint), indicating that it could act as ‘comfort food’. Exposure to diets high in fat and sugar, or just high in sugar, given as 10% sucrose solution, produce cognitive deficits, particularly in hippocampal-dependent spatial tasks, and the behavioural deficit correlated with expression of inflammatory markers in the hippocampus. Of note, obesity-related inflammatory changes have been found in the human brain. The diets also lead to reduced diversity of gut microbiome, and we have investigated various interventions aimed at ‘rescuing’ the diet-related gut dysbiosis to explore whether cognitive changes can be reversed. Probiotics have mixed effects on cognition while the antibiotic anti-inflammatory agent minocycline could ameliorate the impact of a diet high in fat and sugar on hippocampal-dependent memory performance. Other work is investigating the impact of enriching certain presumed beneficial bacteria in rats consuming the western diet.