Aims: High-fat, high-sugar diets are associated with impaired cognitive function and altered gut microbiome composition. Research on the ‘gut-brain axis’ indicates that specific microbial taxa and metabolites in the gut can alter behaviour and brain function. However, whether diet-induced alterations of the gut microbiome directly cause cognitive impairments remains unclear. This experiment investigated the mechanistic relationship between diet-induced changes in gut microbiota and cognitive outcomes using faecal microbiota transplantation (FMT).
Method: Adult male Sprague-Dawley donor rats were fed a healthy chow or high-fat, high-sugar ‘Cafeteria’ (CAF) diet for 12 weeks. Faecal samples were collected from individual donor rats, processed anaerobically, and frozen for later use in FMT. Recipient rats were fed chow throughout experimental procedures. Chow-fed recipient rats were treated with antibiotics to deplete the endogenous microbiome and subsequently received FMT from chow (Chow-FMT, n = 18) or CAF-fed (CAF-FMT; n =18) donors over 3 weeks (oral gavage 3x/wk).
Results: CAF-fed donor rats showed significantly increased body weight, adiposity and blood glucose, impaired spatial memory and altered microbiome composition. In recipient rats, no significant changes in short-term memory (place and object recognition tests) were observed across FMT with performance intact in both groups, despite differences in recipient microbiome composition.
Conclusions: Results suggest that high-fat high-sugar diet-induced cognitive impairment are not driven by altered microbiota composition. Further work is needed to explore potential protective effects of the chow diet fed to recipient rats, which may select for specific microbial strains provided during FMT.