The types of food that a person consumes can have a significant impact on gut microbiota.7 The Western diet, which is high in fat and low in fiber, is linked to a decrease in overall total bacteria and beneficial Bifidobacterium and Eubacterium species.8,9 This alteration can lead to mucus degradation, reduced levels of short-chain fatty acids, and increased susceptibility to invading pathogens.8,10 Bifidobacterium and Eubacterium species and overall total bacteria count are increased with high-fiber diets, such as the Mediterranean diet.8,9,11
Infection is one of the most common causes of dysbiosis.12 Colonization by pathogenic bacteria can induce inflammation in the GI tract. This inflammatory state can destabilize the gut microbiota community, resulting in an imbalance in composition and function. In addition, pathogens can outcompete commensal bacteria, resulting in overgrowth of infectious bacteria.13
Microbial diversity increases in early childhood and stabilizes at age 3.14-16 After age 70, immune system weakness and changes in physical activity, digestion, and nutrient intake can affect microbial composition. The resulting dysbiosis can trigger a proinflammatory state that may be linked to health issues, such as malnutrition and tumorgenesis.15,16
Psychological stress can affect gut motility, visceral perception, GI secretion, and intestinal permeability. These effects on the GI tract can negatively alter the composition of gut microbiota.3,17
Certain medications, such as antibiotics and proton pump inhibitors, can alter gut microbial composition.8,18 Proton pump inhibitors reduce acidity in the GI tract, creating a higher luminal pH, which can promote small intestinal bacterial overgrowth.8 Antibiotic use can diminish taxonomic diversity, which can persist over time.18,19
Cigarette smoking has been linked to changes in the composition of gut microbiota. Analyses using high-throughput sequencing have shown profound and robust microbial shifts before and after smoking cessation.20 Alcohol consumption also has a known influence on gut microbiota composition and function, but more studies are needed to validate the impact.21,22
Habitual exercise is associated with increased diversity and abundance of gut microbiota and boosts production of beneficial short-chain fatty acids.16
Current research supports that gut microbiota, in some capacity, contribute not only to the maintenance of GI health but also to the development of many GI diseases.23
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