How plant-based, Mediterranean, and Western diets affect gut microbiota and disease

A recent study published in Nutrients examines how different dietary components affect the gut microbiome and the development of non-communicable diseases (NCDs).

Diet and gut microbiome

To date, over 2,000 species of bacteria, viruses, Archaea, and protists have been identified within the human microbiome.

Fiber is broken down by a healthy and diverse gut microbiome through fermentation, which leads to the production of anti-inflammatory metabolites that promote a longer lifespan. Compared to traditional rural diets that are high in fiber, the low fiber and high fat content of Westernized diets reduce microbiome diversity and promote inflammation.

The microbiome at various levels of the gut

Additional pathogens in the colon include Escherichia coli, Vibrio cholerae, Bacteroides fragilis, and Campylobacter jejuni, which comprise about 0.1% of the total bacteria.

Functions of the gut microbiota

Dietary fiber is fermented by gut microorganisms to yield various products, including short-chain fatty acids (SCFAs) like acetate, butyrate, and propionate. SCFAs are absorbed by the gut epithelium and used as energy sources.

SCFAs also affect host metabolism by regulating transcription, the cell cycle, epithelial integrity, and appetite regulation. These fatty acids are also involved in mucosal immunity through immunoglobulin A (IgA) production and reduce blood pressure.

Gut bacteria synthesize Vitamin K, folate, and other B-group vitamins. These vitamins support the reabsorption of bile acids by producing secondary from primary bile acids, thereby promoting lipid digestion and absorption. They also activate polyphenols to increase their absorption.

Gut microorganisms also break down lecithin and choline from fats to trimethylamine-N-oxide (TMAO). TMAO promotes atherogenesis by increasing cholesterol absorption, reducing cholesterol levels, and activating platelets. Phenylacetylglutamine (PAG), which is also a metabolite derived from the breakdown of dietary protein and amino acids, regulates cardiovascular function and blood pressure.

The gut-brain axis is a bidirectional network that connects the central, autonomic, and enteric nervous systems to the hypothalamo-pituitary-adrenal axis. Crosstalk in the gut-brain axis is mediated by bacterial metabolites, including neurotransmitters like serotonin and dopamine. Gram-negative bacteria can also induce lipopolysaccharide synthesis, which triggers inflammatory cytokines that can have adverse effects on the central nervous system (CNS).

Factors affecting the gut microbiota

The infant gastrointestinal tract is seeded from the mother’s, with subsequent alterations in the microbiome composition derived from infections, antibiotics, diet, immune responses, and genetic influences.

By 65 years of age, bacterial diversity declines, and facultative anaerobes increase in abundance. Drinking, smoking, and exercise also affect the composition of the gut microbiota, thereby suppressing nutrient absorption, changing the gut pH and oxygen levels, and reducing immunity.

Gut microbiota and disease

Other medical conditions related to dysbiosis include diabetes mellitus, neuroinflammatory conditions like Parkinson's disease and Alzheimer’s disease, and psychological disorders like depression, anxiety, and autism spectrum disorder (ASD).

Diets and gut microbiota

Plant-based and Mediterranean diets are rich in fiber, which supports SCFA production and suppresses harmful metabolites like TMAO. These diets reduce the risk of cancer, diabetes, and metabolic disorders

The Mediterranean diet provides polyunsaturated fatty acids (PUFAs), which, like SCFAs, have anti-inflammatory and cardioprotective properties. This dietary pattern also provides iron and zinc, which activate the immune system.

Conclusions

Numerous studies have established the nutritional and health outcome-related superiority of plant-based and Mediterranean diets as compared to the Western diet. These dietary patterns support healthy gut microbiome growth while also preventing NCDs. Nevertheless, additional research is needed to identify novel therapeutic approaches that personalize diets to prevent and manage chronic disease.

Journal reference:

• Soldan, M., Argalasova, L., Hadvinova, L., et al. (2024). The Effect of Dietary Types on Gut Microbiota Composition and Development of Non-Communicable Diseases: A Narrative Review. Nutrients. doi:10.3390/nu16183134.