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

## TL;DR

Carbohydrate-heavy diets change gut microbes differently, with high-fat carbs linked to obesity-related shifts and low-fat carbs having mixed effects.

## Contribution

This systematic review reveals how different carbohydrate diets uniquely affect gut microbiome composition and related health outcomes in animals.

## Key findings

- High-fat carbohydrate diets consistently increase the Firmicutes/Bacteroidetes ratio, associated with obesity.
- Low-fat carbohydrate diets produce diverse microbiome effects, ranging from beneficial to harmful.
- Interventions can modulate diet-induced changes in gut microbiota and related pathophysiology.

## Abstract

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.

Carbohydrate‐loading diets alter the gut microbiome differently. High‐fat carbs raise the Firmicutes/Bacteroidetes (F/B) ratio, which is linked to obesity, while low‐fat carbs cause varied effects. Outcomes depend on carbohydrate type and other factors, highlighting the need for further research.