The Correlation Between Carbohydrate Loading Diet and Gut Microbiome: A Systematic Review

The gut microbiome critically influences digestion, mucosal permeability, metabolism, blood pressure, and lipid profile. Pathological shifts in these processes cause metabolic syndrome, a growing human health concern that may be modeled in animals with carbohydrate-loading diets. We reviewed the effects of carbohydrate-loading diets on the animal gut microbiome. A systematic literature search was performed up to September 2024 on five databases: Cochrane Library, PubMed, Scopus, Web of Science, and VHL. Relevant animal studies were assessed for risk of bias using SYRCLE's tool. Seventeen studies were included, with data from more than 690 rodents. Carbohydrate-loading diets alter the gut microbiome composition, diversity, and ratios. High-carbohydrate, high-fat diets were almost consistently associated with an increased Firmicutes to Bacteroidetes (F/B) ratio. Different types of carbohydrates, such as fructose, sucrose, or even special diet types, vary widely in impacting both the microbiota and microbiota-associated pathophysiology, inducing different metabolic states and affecting blood pressure, gut structural integrity, immunomodulation, and other functions. Interventions added with or after feeding substantially modulated these diet-induced changes. Carbohydrate-loading diets can differentially influence the gut microbiome and associated physiology. High-fat carbohydrate diets, apart from starch-based diets, typically increase the F/B ratio, a shift linked to human obesity. In contrast, low-fat carbohydrate diets do not elevate the F/B ratio but instead produce diverse microbiome effects, ranging from beneficial to harmful, depending on the carbohydrate type and other influencing factors. Further animal and human research is crucial to validate and further illuminate the dietary impact on the gut microbiome.