How does gut microbiota affect health? Diabetes, fatty liver, colorectal cancer, inflammation may be related!
1、 The basic distribution of the gut microbiome: from the oral cavity to the colon, the microbial concentration increases from millions/gram to billions/gram. The small intestine is mainly composed of oxygen tolerant bacteria (streptococcus, lactobacillus), while the colon is mainly composed of anaerobic bacteria (Firmicutes, Bacteroidetes), formed by screening the digestive tract microenvironment (gastric acid, bile acid).
Health characteristics: It is necessary to meet the requirements of "high diversity" (thousands of microorganisms) and "functional balance", with core beneficial bacteria including short chain fatty acid (SCFA) producing fecal bacteria and mucinous protein metabolizing Akkermansia.
Imbalance triggers: high sugar and high-fat diet, antibiotic abuse, and aging (decreased NAD+synthesis after the age of 30) can disrupt the balance of the microbiota.
2、 Association between flora imbalance and disease/obesity/type 2 diabetes (T2D)
The number of SCFA producing bacteria (such as fecal bacteria) decreased by more than 50%, and the proportion of pro-inflammatory Enterobacteriaceae (such as Escherichia coli) significantly increased.
The abundance of toxin producing Escherichia coli in non-alcoholic fatty liver disease (NAFLD) increased, and the number of Clostridium difficile (such as Bifidobacterium) that can convert bile acids decreased
The microbial diversity of inflammatory bowel disease (IBD, including ulcerative colitis and Crohn's disease) has sharply decreased (only one-third of that of healthy individuals), and anti-inflammatory fecal bacteria have almost completely disappeared.
The proportion of facultative anaerobic Proteobacteria (such as adherent invasive Escherichia coli) is three times higher than normal levels
The abundance of carcinogenic bacteria (such as Clostridium nucleatum and Bacteroides fragilis) in colorectal cancer (CRC) has increased, and some oral pathogenic bacteria (such as Clostridium nucleatum) have colonized the intestine
3、 How do microbiota regulate health?
Intestinal inflammation: The microbiota ferments dietary fiber to produce (acetic acid, propionic acid, butyrate), which is the "energy source" of colon cells. Butyrate can also activate GPR41/43 receptors, promote GLP-1 secretion (regulate blood sugar, control appetite), and inhibit intestinal inflammation.
Liver lipid metabolism and insulin: Primary bile acids synthesized by the liver are converted into secondary bile acids by the microbiota, which regulate liver lipid metabolism and insulin sensitivity by activating FXR/TGR5 receptors, and can also inhibit the growth of harmful bacteria.
Inflammation such as celiac disease: The microbiota metabolizes tryptophan to produce ligands (such as indole-3-aldehyde), which activate AhR to promote tight junction of intestinal epithelium (barrier protection), induce anti-inflammatory Treg cells, and alleviate inflammation such as celiac disease.
Adipose inflammation and insulin resistance: Healthy microbiota promotes anti-inflammatory eCB production (protecting the intestinal barrier), while imbalanced microbiota during obesity leads to an increase in pro-inflammatory eCB, exacerbating adipoinflammation and insulin resistance, forming a bidirectional effect of "microbiota eCB".
