High fructose corn syrup (HFCS) has become a prevalent sweetener, raising concerns about its impact on health. Excessive HFCS consumption is linked to obesity, insulin resistance, non-alcoholic fatty liver disease (NAFLD), cardiovascular diseases, type 2 diabetes, reproductive issues, and even cancer. The gut microbiota plays a crucial role in metabolism and is implicated in various chronic diseases. While the metabolic effects of HFCS are studied, its influence on gut microbiota is less understood. This study used 16S rDNA sequencing to analyze the effects of HFCS on the intestinal microbiota diversity and composition in mice, and to explore the correlation between gut microbiota changes and obesity indicators. The aim is to understand the potential mechanisms through which HFCS alters the gut microbiome and contributes to obesity.

Existing research primarily focuses on the metabolic consequences of HFCS, such as NAFLD and diabetes, with limited investigation into its effects on the gut microbiome. Studies have shown varying results regarding the impact of high-fat diets on the Firmicutes/Bacteroidetes ratio in the gut. Some report an increase, while others report a decrease. The role of specific gut bacterial genera, such as *Christensenellaceae*, in obesity and metabolic health is also a subject of ongoing research, with some evidence suggesting a negative correlation between its abundance and obesity.

Sixteen male C57BL/6J mice (3 weeks old) were randomly divided into a control group and an HFCS group (n=8 each). The HFCS group received drinking water containing 30% (w/v) HFCS, while the control group received pure water. Both groups received a standard diet ad libitum for 16 weeks. Body weight, perirenal fat, epididymal fat, and liver fat percentage were measured. Colonic contents were collected for 16S rDNA sequencing to analyze the gut microbiota composition. Liver tissues were stained with Oil Red O to visualize lipid accumulation. Statistical analysis was performed to determine significant differences between groups and correlations between microbiota composition and obesity indicators.

Long-term consumption of 30% HFCS drinking water significantly increased body weight, perirenal fat, epididymal fat (p=0.001, p=0.0009, p=0.007, respectively), and liver fat percentage (p<0.0001) in mice. HFCS consumption reduced the richness of the colonic microbiota. Beta-diversity analysis revealed significant differences in gut microbiota composition between the HFCS and control groups. At the genus level, several bacteria showed altered abundance, including *Tyzzerella*, *Erysipelatoclostridium*, *Helicobacter*, and *Christensenellaceae* R-7 group. *Tyzzerella*, *Erysipelatoclostridium*, and *Helicobacter* were positively correlated with obesity indicators, while *Christensenellaceae* R-7 group showed a strong negative correlation.

The increase in body weight and visceral fat aligns with previous studies. The observed changes in gut microbiota composition, particularly the negative correlation between *Christensenellaceae* R-7 group and obesity indices, suggest a potential mechanism by which HFCS contributes to obesity. Previous research has linked *Christensenellaceae* abundance to body mass index and metabolic health. The decrease in this genus in the HFCS group may be a contributing factor to increased fat accumulation. The positive correlation of other genera with obesity warrants further investigation.

This study demonstrates that long-term consumption of HFCS in mice leads to obesity and significant alterations in gut microbiota composition. The negative correlation between *Christensenellaceae* R-7 group and obesity suggests a potential role of this bacterial genus in mediating the effects of HFCS. Further research is needed to elucidate the specific mechanisms involved and to explore the translational implications for human health.

This study used a mouse model, and the results may not directly translate to humans. The study focused on a single concentration of HFCS and a specific mouse strain, limiting the generalizability of the findings. Further research is needed to investigate the effects of different HFCS concentrations and various dietary factors on the gut microbiota.