It’s the fiber, not the fat: Significant effects of dietary challenge on the gut microbiome

Abstract

BackgroundDietary effects on the gut microbiome has been shown to play a key role in the pathophysiology of behavioral dysregulation, inflammatory disorders, metabolic syndrome, and obesity. Often overlooked is that experimental diets vary significantly in the proportion and source of dietary fiber. Commonly, treatment comparisons are made between animals that are fed refined diets that lack soluble fiber and animals fed vivarium-provided chow diet that contain a rich source of soluble fiber. Despite the well-established role of soluble fiber on metabolism, immunity, and behavior via the gut microbiome, the extent to which measured outcomes may be driven by differences in dietary fiber is unclear. Further, the significant impact of sex and age in response to dietary challenge is likely important and should also be considered.\n\nResultsWe compared the impact of transitioning young and aged male and female mice from a chow diet to a refined low soluble fiber diet on body weight and gut microbiota. Then, to determine the contribution of dietary fat, we examined the impact of transitioning a subset of animals from refined low fat to refined high fat diet. Serial tracking of body weights revealed that consumption of low fat or high fat refined diet increased body weight in young and aged adult male mice. Young adult females showed resistance to body weight gain, while high fat diet-fed aged females had significant body weight gain. Transition from a chow diet to low soluble fiber refined diet accounted for most of the variance in community structure and composition across all groups. This dietary transition was characterized by a loss of taxa within the phylum Bacteroidetes and a concurrent bloom of Clostridia and Proteobacteria in a sex- and age-specific manner. Most notably, no changes to gut microbiota community structure and composition were observed between mice consuming either low- or high-fat diet, suggesting that transition to the refined diet that lacks soluble fiber is the primary driver of gut microbiota alterations, with limited additional impact of dietary fat on gut microbiota.\n\nConclusionCollectively, our results show that the choice of control diet has a significant impact on outcomes and interpretation related to body weight and gut microbiota. These data also have broad implications for rodent studies that draw comparisons between refined high fat diets and chow diets to examine dietary fat effects on metabolic, immune, behavioral, and neurobiological outcomes.