Probiotics are beneficial active microorganisms that colonize the human intestines and change the composition of the flora in particular parts of the host. Recently, the use of probiotics to regulate intestinal flora to improve host immunity has received widespread attention. Recent evidence has shown that probiotics play significant roles in gut microbiota composition, which can inhibit the colonization of pathogenic bacteria in the intestine, help the host build a healthy intestinal mucosa protective layer, and enhance the host immune system. Based on the close relationship between the gut microbiota and human immunity, it has become an extremely effective way to improve human immunity by regulating the gut microbiome with probiotics. In this review, we discussed the influence of probiotics on the gut microbiota and human immunity, and the relationship between immunity, probiotics, gut microbiota, and life quality. We further emphasized the regulation of gut microflora through probiotics, thereby enhancing human immunity and improving people’s lives.

Increasing evidence has confirmed that whole grain oats are effective in regulating hyperlipidemia. However, which specific ingredient is crucial remains unclear. This study focused on which whole grain components, oat phenolic compounds (OPC) or oat β-glucan (OBG), can regulate lipid metabolism and gut microbiota. The experiment unveiled that OPC and/or OBG not only reduced the body weight and fasting blood glucose (FBG) but also regulated serum and hepatic lipid levels in high-fat-diet (HFD) fed mice. There was no significant difference in the regulatory effects of OPC and OBG (p > 0.05). The combination of OPC and OBG (OPC + OBG) significantly decreased the body weight (p < 0.01) and reduced the blood glucose (p < 0.01) and lipid profile levels (p < 0.01). The real-time quantitative PCR (RT-qPCR) study revealed that OPC + OBG significantly altered mRNA expression related to lipid metabolism. Histopathological analysis showed that OPC + OBG improved liver lipid deposition as well as liver oxidative stress (p < 0.05). In addition, OPC + OBG combination regulated the gut microbiota community phenotype and increased probiotics. OPC + OBG significantly increased the abundance of Bacteroidetes and reduced the abundance of Firmicutes (p < 0.05) compared with the OPC and OBG fed mice. In conclusion, OPC + OBG has a synergistic effect in alleviating hyperlipidemia via lipid metabolism and gut microbiota composition. This finding also provided a potential justification for the advantages of whole grains in preventing hyperlipidemia.