One third of dietary energy intake of Australians comprises discretionary foods high in fat and sugar (HFHS), which have been shown to impair cognition and alter gut microbiota composition. Such HFHS foods commonly form part of diverse diets. The cognitive effects of cycling between obesogenic and healthy diets are unclear. Here we tested whether HFHS diet-induced cognitive impairments were sensitive to (a) diet withdrawal; (b) intermittent or (c) time-restricted access; and (d) individual differences in HFHS consumption.
Method and results: We assessed recognition memory, adiposity and gut microbiota composition in adult male Sprague-Dawley rats cycled between HFHS ‘cafeteria’ (Caf) and regular chow diet. To examine effects of varying Caf cycle length, we provided 16 days of Caf diet in 2, 4, 8 or 16-day cycles, each separated by 4-day chow cycles (n=12/group). Place recognition memory declined from baseline across groups, with significantly worsening in the 16-day versus 2-day group. To examine the effects of varying chow cycle length, we provided 24 days of Caf diet continuously or in 3-day cycles separated by 2- or 4- day chow cycles. Any Caf diet access impaired place recognition memory and increased adiposity relative to control. Changes in faecal microbiota composition were greater in groups with a higher percentage of time on Caf. Place recognition memory and whole body adiposity were the strongest phenotypic predictors of global microbiota composition. Limiting Caf feeding to 8 hours daily had no benefit for cognition but ameliorated some of the metabolic impacts.
In conclusion, diets with higher Caf:chow ratios produced more pronounced spatial memory impairments, larger reductions in gut microbiota species richness and greater shifts in beta diversity. Thus diet-induced cognitive deficits appear proportional to unhealthy diet exposure, and shifting rats to healthy chow diet for at least a week is required for recovery under conditions tested here.