Parabacteroides is a genus of Gram-negative, anaerobic bacteria naturally residing within the human gastrointestinal tract, forming a significant component of the normal gut microbiota, particularly in the colon. P. distasonis and P. goldsteinii are among the most frequently studied species for their roles in human health.
Role in Gut Metabolism
Parabacteroides species play a role in gut metabolism by breaking down complex carbohydrates, such as dietary fibers. P. distasonis and P. goldsteinii participate in this process, leading to the production of short-chain fatty acids (SCFAs) like acetic and succinic acids. These SCFAs serve as important energy sources for gut cells and contribute to overall gut health.
Beyond carbohydrate fermentation, Parabacteroides also performs a function in metabolizing bile acids. P. distasonis has the capacity to transform primary bile acids into secondary bile acids, including lithocholic acid (LCA) and ursodeoxycholic acid (UDCA). These secondary bile acids are signaling molecules that can activate specific host receptors, such as the farnesoid X receptor (FXR), involved in regulating lipid and glucose metabolism.
The production of succinate by Parabacteroides is another metabolic contribution. This metabolite can promote intestinal gluconeogenesis, a process where the gut produces glucose, which can influence host energy balance. The ability of these bacteria to modify bile acids and produce succinate highlights their intricate involvement in host metabolic pathways, extending beyond simple digestion.
Association with Health and Disease
Research indicates correlations between Parabacteroides levels and health conditions. Species such as P. distasonis and P. goldsteinii are often associated with protective effects against metabolic syndrome, obesity, and type 2 diabetes. Studies in animal models have shown that these bacteria can help reduce weight gain, lower high blood sugar levels (hyperglycemia), and alleviate fatty liver conditions (hepatic steatosis).
The beneficial metabolic effects are linked to the bacteria’s metabolic activities, including their role in bile acid transformation and succinate production. P. distasonis can also contribute to attenuating insulin resistance by helping to repair the intestinal barrier and reducing inflammation. These effects suggest that a balanced presence of Parabacteroides may contribute to maintaining metabolic homeostasis.
The role of Parabacteroides in inflammatory bowel disease (IBD) is complex, with some studies indicating a protective association. Certain strains of P. distasonis have shown anti-inflammatory effects and can support the restoration of gut barrier function in models of colitis. Conversely, a reduction in P. distasonis has been noted in the gut microbiota of individuals with inflammatory conditions like multiple sclerosis and rheumatoid arthritis.
The gut microbiota may influence the effectiveness of certain cancer immunotherapies. Specific bacterial compositions in the gut have been correlated with better responses to treatments like checkpoint blockade immunotherapy. P. distasonis has been observed to stimulate the production of interleukin-10 (IL-10) by regulatory T cells, which could play a role in modulating immune responses within the tumor microenvironment.
Interaction with the Immune System
Parabacteroides interacts directly with the host’s immune system, contributing to gut barrier integrity and immune regulation. P. distasonis, for example, can enhance the strength and stability of the intestinal barrier. This barrier acts as a protective shield, preventing harmful substances and unwanted microbes from entering the bloodstream and triggering systemic inflammation.
Some strains of Parabacteroides have been shown to restore the expression of tight junction proteins, such as occludin, which are important for maintaining the epithelial barrier’s seal. This reinforcement helps reduce intestinal permeability, often referred to as “leaky gut,” thereby preventing immune overactivation. Strengthening this barrier is an important way these bacteria contribute to overall immune balance.
The genus also contributes to immune modulation through the production of anti-inflammatory molecules. P. distasonis can promote anti-inflammatory mechanisms within the adaptive immune system, specifically by stimulating regulatory T cells. These T cells are known for producing anti-inflammatory cytokines like IL-10, which help to dampen excessive immune responses and maintain gut homeostasis.
Influencing Parabacteroides Levels
Supporting a healthy population of Parabacteroides in the gut can be achieved through dietary choices, by consuming diverse dietary fibers. These complex carbohydrates act as prebiotics, providing nourishment for Parabacteroides and other beneficial gut bacteria. Incorporating a variety of vegetables, fruits, legumes, and whole grains into the diet can help foster a thriving gut microbial community.
Studies have indicated that the regular consumption of cereals, such as fruit granolas and cornflakes, can lead to an increase in the abundance of Parabacteroides. This demonstrates how simple dietary adjustments can directly impact the composition and function of the gut microbiota. A consistent intake of these fibers ensures a steady food supply for these beneficial microbes.
Beyond fibers, polyphenols, natural compounds in plant-based foods, can also influence Parabacteroides levels. These compounds are abundant in foods like berries, dark chocolate, green tea, and various fruits and vegetables. When consumed, polyphenols interact with gut bacteria, and their fermentation can enhance the growth of beneficial species, including those within the Bacteroidetes phylum, to which Parabacteroides belongs.