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With the improvement of living standards and the change of dietary habits, metabolic syndrome has become a major global public health problem. The gut microbiota is one of the research hotspots in recent years. More and more studies have shown that the gut microbiota can conduct bidirectional signal transduction with different body tissues and organs such as the brain, liver and heart through various pathways, which is closely related to body health. Medium-chain fatty acids (MCFAs) exist in coconut oil, palm kernel oil and dairy products mainly in the form of medium-chain triglycerides (MCTs). MCFAs can be rapidly metabolized for energy in the body, and has good regulatory effects on glucose and lipid metabolism. This article reviews the effects of MCTs on gut microbes and their positive effects on metabolic syndrome in order to provide a reference for future research.

Food preservatives are widely used in the food industry for their broad antibacterial spectrum and strong antibacterial properties. While the effects of dietary food preservatives on the gut microbiota and host health have been studied, a systematic review is lacking. In this paper, the latest research on food preservatives and the gut microbiota is reviewed. It has been found that food preservatives affect lipid metabolism, immunity and intestinal inflammation by altering the diversity of the gut microbiota and regulating the abundance of conditioned pathogens and beneficial bacteria. The future research trends are also discussed. Through this review, we hope that the ‘food preservatives-gut microbiota-host health’ chain can arouse the attention of researchers and readers, and provide a new perspective for the existing safety evaluation system of food preservatives, which may be of guiding significance for the maintenance of human health.

The altered circulating bile acids (BAs) modulate gut microbiota, energy metabolism and various physiological functions. BA profiles in liver, serum, ileum and feces of HFD-fed mice were analyzed with normal chow diet (NCD)-fed mice after 16-week feeding. Furthermore, gut microbiota was analyzed and its correlation analysis with BA was performed. The result showed that long-term HFD feeding significantly decreased hepatic and serum BA levels, mainly attributed to the inhibition of hepatic BA synthesis and the reduced reabsorption efficiency of BAs in enterohepatic circulation. It also significantly impaired glucose and lipid homeostasis and gut microbiota in mice. We found significantly higher bile salt hydrolase activity in ileal microbes and a higher ratio of free BAs to conjugated BA content in ileal contents in HFD groups compared with NCD group mice, which might account for the activated intestinal farnesoid X receptor signaling on liver BA synthesis inhibition and reduced ileal reabsorption. The decreased circulating BAs were associated with the dysregulation of the lipid metabolism according to the decreased TGR5 signaling in the ileum and BAT. In addition, it is astonishing to find extremely high percentages of taurocholate and 12-OH BAs in liver and serum BA profiles of both groups, which was mainly attributed to the high substrate selectivity for 12-OH BAs of the intestinal BAs transporter during the ileal reabsorption of enterohepatic circulation. This study revealed a significant effect of long-term HFD feeding on the decreased circulating BA pool in mice, which impaired lipid homeostasis and gut microbiota, and collectively resulted in metabolic disorders and obesity. [ABSTRACT FROM AUTHOR]

Sodium benzoate (SB) is a common food preservative widely used in the food industry. However, the effects of SB intake on host health at different stages were still unclear. Hence, we investigated the impact of SB with three concentrations (150 mg/kg, 500 mg/kg and 1000 mg/kg) and at three stages (intake for 5-weeks, intake for 10-weeks and removal for 5 weeks) on host health in normal mice. The results showed that SB intake for 5 weeks slightly changed gut microbiota composition, but it significantly increased TG (only 150 mg/kg and 1000 mg/kg) and blood glucose levels (only 500 mg/kg) and promoted the secretion of interleukin (IL)-1β and IL-6 (p < 0.01). However, SB intake for 10 weeks mostly maintained normal glucolipid metabolism; although, IL-1β (p < 0.01) and IL-6 (p < 0.05) levels were also significantly increased and positively regulated the gut microbiota by significantly increasing the relative abundance of Lactobacillus and significantly decreasing the relative abundance of Ileibacterium. Meanwhile, the safety of SB for host metabolism and gut microbiota was also confirmed via a fecal microbiota transplantation experiment. In addition, we found that SB removal after 10 weeks of intake significantly increased the levels of blood glucose, insulin and HOMA-IR index, which might be attributed to gut microbiota dysbiosis. Mechanistically, these positive effects and negative effects had no close relationship with the concentration of short-chain fatty acids in the gut, which might be associated with metabolites of SB or special bacterial strains. In short, this work provided positive evidence for the safety of SB consumption within the recommended range. [ABSTRACT FROM AUTHOR]