Factors able to modify gut microbiota include different medications. Antibiotics are expected to have a large effect, but also other common medications can have an impact on gut microbiota composition. Proton-pump inhibitors (PPIs) are, for example, associated with a higher Streptococcaceae and Micrococcaceae abundance and a lower microbiota diversity. Also, paracetamol and opioids are associated with an increase of Streptococcaceae, whereas serotonin reuptake inhibitors (SSRIs) are negatively associated with Turicibacteraceae. Moreover, inhaled anticholinergics are negatively associated with Ruminococcaceae and Peptococcaceae abundance and microbiota diversity. Herbs can modulate gut microbiota too. For example, ginseng administration has been associated with the decrease in bacteria that possibly promote tumorigenesis (such as Bacteroidales and Verrucomicrobia) and an increase in bacteria that possibly exert antiinflammatory and anti-cancer activities (such as Firmicutes).
Diet is another major regulator of gut microbiota structure and function. Its contribution to microbiota modulation and host-microbiota crosstalk is evident from the beginning of life, with human milk oligosaccharides participating in microbiota development and solid food introduction increasing bacterial richness. However, in the elderly, where food diversity is reduced, microbiota richness decreases, too. Some nutrients (such as glycans, quinones, and flavonoids) directly interact with bacteria, promoting or inhibiting their growth. Moreover, dietderived compounds can indirectly shape gut microbiota by affecting host metabolism and the immune system. Vitamin D, for example, is associated with a decrease in circulatory levels of LPS, decreased abundance of Coprococcus and Bifidobacterium, and increased abundance of Prevotella, and dietary constituents (such as selected emulsifiers) might disrupt the intestinal barrier.
