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Addition of soluble fiber in low fat purified diets improves gut and metabolic health compared to traditional AIN diets

Background Purified diets (PDs) contain refined ingredients with one main nutrient, allowing for greater control relative to grain-based diets (GBDs), which contain unrefined grains and animal byproducts. Traditional PDs like the AIN-76A (76A) and AIN-93G (93G) can negatively impact metabolic and gut health when fed long-term, in part due to lower total fiber, no soluble fiber, and higher sucrose content. Objective Two studies were conducted to determine how PDs with reduced sucrose and increased fiber (soluble and insoluble) influence metabolic and gut health in mice compared to traditional AIN PDs or GBDs. Methods In study 1, C57Bl/6N mice consumed a GBD (5002), 76A, 93G, or 2 Open standard PDs (OSDs) with reduced sucrose and higher fiber for 88 days. Body composition and metabolic parameters were assessed. In study 2, C57Bl/6N mice consumed either 2 GBDs (5001 or 5002) or OSDs with different types/levels of fiber for 14 days. Microbiome alterations and predicted functional metagenomic changes were measured. Results OSD marginally influenced body weight and adiposity, but improved glucose tolerance relative to 93G (p = 0.0131) and 76A (p = 0.0014). Cecal and colonic weights were lower in mice fed cellulose-based PDs compared to those fed GBDs and soluble fiber PDs. Soluble fiber diets reduced alpha diversity and showed similar beta diversity, which differed from cellulose fed PDs and GBDs. Certain genera associated with improved gut health such as Bifidobacteria and Akkermansia were significantly elevated by soluble fibers PDs (p≤0.01). Some metabolic pathways related to carbohydrate and fatty acid metabolism were affected by PDs. Conclusion PDs formulated with lower sucrose and increased fiber content, particularly soluble fiber, blunted elevations in metabolic parameters and favorably impacted microbiota and metagenome in C57BL/6N mice.