Added sugars, gut microbiota, and host health.

Excessive intake of added sugars is a global public health concern, given its established links with cardiometabolic disease and other chronic conditions. Emerging evidence suggests that the gut microbiota might mediate the harms of high sugar intake. In this review, we summarize evidence from animal and human studies regarding the impact of added sugar intake on gut microbiota diversity and composition, and discuss potential mechanisms linking sugar-induced microbial changes to health outcomes. Added sugars, including glucose, fructose, and sucrose, can alter gut microbial diversity, enrich sugar-utilizing taxa, and deplete short-chain fatty acid-producing bacteria. These microbial changes may impair gut barrier integrity, increase luminal oxygen and alternative electron acceptors under inflammatory conditions, reduce short-chain fatty acid production, alter bile acid and amino acid metabolism, and promote translocation of endotoxin across the gut barrier into the bloodstream. Collectively, these pathways may link added sugar intake to irritable bowel syndrome, obesity, liver steatosis, diabetes, and cardiovascular diseases. However, inconsistent results on alterations in the gut microbiota related to added sugar intake were observed across studies, which may be due to differences in sugar dose and form (liquid vs. solid), as well as population variation in background diet, host genetics, and gut microbial ecology. Future research should focus on mechanistic investigations, characterization of inter-individual variability in response to added sugar intake, and clinical studies to assess whether dietary or therapeutic interventions can reverse sugar-induced gut microbial changes and improve host health outcomes.