Under the catalysis of a series of enzymes, such as amylase and glucose isomerase, corn starch is converted into a mixture of glucose and fructose to form fructose corn syrup (FCS). FCS with a fructose to glucose ratio of 55:45 is mainly used in the production of soft drinks. Due to its low price and high sweetness, FCS has become the main sweetener and energy sources in beverages [1]. Since the large-scale commercial application of FCS in the 1970s, the increase in intake of soft drinks has been found to be closely related to the occurrence of obesity [2].

With the development of large-scale sequencing in recent years, the important role of gut microbiota in metabolic diseases has received widespread attention. The abnormal composition and/or function of the gut microbiota may lead to abnormal energy metabolism and immune function, affecting multiple tissues and organs. Diet was proven to affect the structure of the gut microbiota with specific changes to the major macronutrient contained in the diet. Compared to the control group, mice fed a high fat/high sugar diet showed increased inflammation and great differences in gut microbiota abundance [3]. Randomized crossover studies have also shown that excessive consumption of FCS is associated with multiple metabolic diseases, including hyperlipemia, visceral fat deposition and insulin resistance [4,5].

Most of the current research is centered on the composition of gut microbiota in vivo, with little research on the direct impact of sugar on the metabolic function of gut microbiota. The in vitro fermentation experiments are used to simulate the metabolic function of gut microbiota in anaerobic environments, which can eliminate host interference and explore the direct impact of gut microbiota on substances [6]. Integrating multiple omics studies to investigate the impact of gut microbiota on hosts is becoming increasingly common [7]. However, few studies systematically combined metagenomics and metabolomics to investigate the effects of FCS on the metabolic function of intestinal microbiota. Therefore, combining in vivo and in vitro experiments to study the impact of FCS on host gut microbiome and health through a multi omics approach is an innovative and systematic approach.

The number of overweight and obese people has more than doubled in the past 40 years [8]. In recent years, since the number of people suffering from metabolic diseases such as obesity and diabetes has gradually increased, the alleviation of metabolic health problems has become a growing public concern [9]. At present, there are still many research gaps in regulatory effect of the FCS-induced gut microbiota dysbiosis in metabolic diseases. On the one hand, existing research mainly applies 16S rRNA gene sequencing to explore the effect of FCS on gut microbiota composition [10], lacking research on gut microbiota function; on the other hand, current research on FCS is mainly focused on in vivo experiment. Therefore, it is difficult to define whether the gut microbiota's response to FCS and its impact on the host are indirect or direct. The present study explored the effects of drinking water supplemented with 30% FCS on the health and gut microbiome in mice. Additionally, the effects of FCS on the composition and metabolites of gut microbiota in mice were also investigated through in vitro fermentation. These findings will aid to elucidate the profound impact of gut microbiota on dietary carbohydrate metabolism and provide targets for the treatment of metabolic diseases.