Human Gut Microbiome
The human microbiota is defined as the total of all microbial taxa associated with human beings. Trillions of bacteria (and above 1000 species), archaea, fungi, and viruses reside in the human gastrointestinal tract. Our gut microbiota has a significant impact on our physiology, health, and disease. For example, an imbalance of the gut has been linked with gastrointestinal conditions such as reflux, peptic ulcers, irritable bowel syndrome, non-alcoholic steatohepatitis, and inflammatory bowel disease. Furthermore, conditions such as obesity, atherosclerosis, type 2 diabetes, cancer, Alzheimer's and Parkinson's disease, autism spectrum disorder, etc., also appear to be linked to unfavorable changes in gut microbiota composition.
Essentially, the food we consume has long-term and acute effects on the gut microbiota ecosystem, and a plant-based diet is beneficial for human health by promoting the development of more diverse and stable microbial systems. Compared to omnivores, vegans display a unique gut microbiota in several characteristics, such as a lower amount of harm-causing pathobionts and a greater number of protective species. The reduced inflammation level gives vegan gut microbiota its protective properties. Phytochemicals such as Polyphenols, which are abundant in plant foods, increase Bifidobacterium and Lactobacillus, providing anti-pathogenic, anti-inflammatory, and cardiovascular protection. Because it is very rich in fiber, a vegan diet increases lactic acid bacteria, such as Ruminococcus, E. rectale, and Roseburia, and reduces Clostridium and Enterococcus species. The number of species that have to break down fiber into short-chain fatty acids increases exponentially with a plant-based diet. Short-chain fatty acids such as acetate butyrate and propionate provide significant health benefits, such as improving immunity, fueling the gut lining, fighting colonic diseases and cancer, and promoting healthy blood sugar levels. PMID: 31058160
When comparing a 20-day vegan and vegetarian (lacto-ovo) diet, significantly different results were produced. Subjects on a vegan diet showed the lowest levels of fecal Lactobacilli and Enterococci, along with lower concentrations of bile acids, coprostanol, and coprostanol plus cholesterol, which is more favorable. In a study comparing bacterial DNA from fecal samples of 20 vegans, 11 lacto-vegetarians, and 29 omnivores. Vegans had a higher ratio of an anti-inflammatory bacterium that produces butyrate and most likely plays a protective role for colonocytes. Vegans also displayed a higher ratio of C. clostridioforme within the C. coccoides grouping. PMID: 24173964
In a study comparing 105 vegans, 144 vegetarians, and an equal number of controls consuming an omnivorous diet, Vegan samples had significantly lower microbial counts than their omnivore counterparts for four bacterial taxa: Bacteroides, Bifidobacterium, E. coli, and Enterobacteriaceae. PMID: 21811294
Studies have noted a link between vegan diets and protection against autoimmune diseases. For example, an analysis of the Adventist cohort found that a vegan diet, but not a vegetarian diet, was associated with a lower risk of hypothyroid disease PMID: 24264226 .
Subjects tested on a conventional Western diet and a raw vegan diet for one month showed results suggesting that the uncooked extreme vegan diet causes a decrease in bacterial enzymes and certain toxic products that have been implicated in colon cancer risk. Four fecal hydrolytic enzymes associated with toxic and inflammatory products diminished during the vegan diet disappeared within two weeks of resuming a conventional diet.
As more in-depth research has focused on vegan diets; the raw vegan diet emerged as a promising treatment for rheumatoid arthritis (RA). During a study where RA patients were assigned to either a raw vegan diet or an omnivorous diet, one month was enough to significantly alter microbiota in the vegan group, while no change was observed in the omnivorous group. Most importantly, the vegan diet decreased RA symptoms in some patients, leading the authors to conclude that changes in the fecal flora are associated with diet-induced changes in disease activity.
References
Kwon, C., Ediriweera, M. K., & Kim Cho, S. (2023). Interplay between Phytochemicals and the Colonic Microbiota. Nutrients, 15(8), 1989. https://doi.org/10.3390/nu15081989
Glick-Bauer, M., & Yeh, M. C. (2014). The health advantage of a vegan diet: exploring the gut microbiota connection. Nutrients, 6(11), 4822-4838. https://doi.org/10.3390/nu6114822 PMID: 25365383
Tomova, A., Bukovsky I., Rembert, E., Yonas, W., Alwarith, J., Barnard, N. D., & Kableova, H. (2019). The Effects of Vegetarian and Vegan Diets on Gut Microbiota. Frontiers in nutrition, 6, 47. https://doi.org/10.3389/fnut. 2019.00047
Tonstad, S., Nathan, E., Oda, K., & Fraser, G. (2013). Vegan diets and hypothyroidism. Nutrients, 5(11), 4642–4652. https://doi.org/10.3390/nu5114642
Zimmer, J., Lange, B., Frick, J. S., Sauer, H., Zimmermann, K., Schwiertz, A., Rusch, K., Klosterhalfen, S., & Enck, P. (2012). A vegan or vegetarian diet substantially alters the human colonic faecal microbiota. European journal of clinical nutrition, 66(1), 53–60. https://doi.org/10.1038/ejcn.2011.141(PMID: 21811294)