Gut Microbiome

Microorganisms also called microbes generally refer to microscopic living things, broadly grouped as bacteria, fungi, viruses, archaea, and protists. They are found everywhere, and the human body harbors about 100 trillion microbes (10-fold the number of human cells), the majority living in the gut. This makes gut microbiome an important aspect of human health (1, 2).  

Many different bacteria species live in the gut, all playing different roles. The diversity of gut microbiome changes over time from birth and is affected by diet, medicines, antibiotics, age, and other environmental factors. The human microbiome is grouped into five families: Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria, and Verrucomicrobiai. Bacteroidetes and Firmicutes make up about 90% of our gut microbiome, and their composition greatly influences many aspects of the human health. A high Firmicutes/Bacteroidetes ratio suggests microbial imbalance that may be the result of increased extraction of calories from food, fat deposition, inflammation, and impaired insulin sensitivity. A low Firmicutes/Bacteroidetes ratio suggests gut microbiome imbalance caused by inflammatory bowel disease and irritable bowel syndrome, all caused by a decline in digestive capacity or constipation (3, 4).

Importance of gut microbiome

1. Affects weight. Gut dysbiosis, which is the imbalance of healthy and unhealthy microbes has been proven to lead to weight gain. This because gut microbiome influences the metabolism of nutrients as well as the expenditure of energy (5).   A lower diversity of gut microbiome is linked with increased body mass index (BMI) and obesity. Studies have shown that obese people tend to have higher levels of Firmicutes and lower levels of Bacteroidetes in their gut (6).
2. Enhances gut health. Bacteria in the gut ferment dietary fiber which is not digested and absorbed in the small intestines, producing short chain fatty acids (SCFA) which the body can use as a source of nutrients. Besides, these SCFAs, play a key role protecting the gut from diseases like colon cancer and bowel disorders like irritable bowel disease (IBD). Butyrate for example show anti-cancer activities by inhibiting the cell growth of cancerous colonocytes (7).
3. Boosts host immunity. Gut microbiota feeds on indigestible fiber and grow in numbers, boosting host immunity by phasing out pathogenic bacteria that cause diseases. Bacteria like Peptostreptococcus, Bifidobacterium, Lactobacillus, and Clostridium are anaerobic (do not need oxygen to grow), thus they thrive well in the colon which is a low oxygen environment, and phase out aerobic harmful bacteria by competing with them for nutrients (8).
4. Enhances brain health. A good diversity of healthy gut microbiome improves the health of the brain as the gut is linked to the brain via millions of nerves. Through the communication with this brain-gut axis, gut microbiome has been proven to have an influence in the development of the brain’s neurological pathways, that impact its functioning (intellect, memory, reading ability, memory, and social skills). For example, majority of the people suffering from irritable bowel disease tend to have mood disorders (9).  

Since the foods we eat influence our gut microbiome, adequate nutrition is therefore prime to boosting gut microbiome. It is advisable to eat a variety of foods to increase the diversity of our gut microbiome.

Fiber rich foods like beans, legumes, whole fruits, and whole grains encourage the growth of healthy gut microbiome such as Bifidobacteria (10). Also fermented foods like yoghurt, kefir, miso, kimchi, kombucha, sauerkraut, and tempeh all contain several healthy bacteria particularly Lactobacilli that boosts our microbiome stores (11). On the other hand, reduce your intake of added sugars or artificial sweeteners. Aspartame for example, stimulates the growth of unhealthy bacteria like Enterobacteriaceae, which are noted for spiking blood glucose levels (12).

Take antibiotics only when necessary, they kill both bad and healthy bacteria. Finally, nursing mothers are encouraged to breastfeed exclusively for at least 6 months, to transfer to their babies’ healthy gut microbiome like Bifidobacteria. Statistics show that children who are breastfed have more beneficial microbiome than bottle-fed babies (13).

REFERENCES

1. Microbes A-Z: Your Questions Answered. Retrieved August 10, 2022, from Amnh.org website: https://www.amnh.org/explore/microbe-facts#:~:text=Microbes%20are%20organisms%20that%20are,we%20call%20viruses%20microbes%20too.
2. Ley, R. E., Peterson, D. A., & Gordon, J. I. (2006). Ecological and evolutionary forces shaping microbial diversity in the human intestine. Cell, 124(4), 837–848. doi:10.1016/j.cell.2006.02.017
3. Azad, M. B., Konya, T., Persaud, R. R., Guttman, D. S., Chari, R. S., Field, C. J., … the CHILD Study Investigators. (2016). Impact of maternal intrapartum antibiotics, method of birth and breastfeeding on gut microbiota during the first year of life: a prospective cohort study. BJOG: An International Journal of Obstetrics and Gynaecology, 123(6), 983–993. doi:10.1111/1471-0528.13601
4. Magne, F., Gotteland, M., Gauthier, L., Zazueta, A., Pesoa, S., Navarrete, P., & Balamurugan, R. (2020). The Firmicutes/Bacteroidetes ratio: A relevant marker of gut dysbiosis in obese patients? Nutrients, 12(5), 1474. doi:10.3390/nu12051474
5. Aoun, A., Darwish, F., & Hamod, N. (2020). The influence of the gut microbiome on obesity in adults and the role of probiotics, prebiotics, and synbiotics for weight loss. Preventive Nutrition and Food Science, 25(2), 113–123. doi:10.3746/pnf.2020.25.2.113
6. Lv, Y., Qin, X., Jia, H., Chen, S., Sun, W., & Wang, X. (2019). The association between gut microbiota composition and BMI in Chinese male college students, as analysed by next-generation sequencing. The British Journal of Nutrition, 122(9), 986–995. doi:10.1017/S0007114519001909
7. The microbiome. (2017, August 16). Retrieved August 10, 2022, from The Nutrition Source website: https://www.hsph.harvard.edu/nutritionsource/microbiome/
8. Valdes, A. M., Walter, J., Segal, E., & Spector, T. D. (2018). Role of the gut microbiota in nutrition and health. BMJ (Clinical Research Ed.), 361, k2179. doi:10.1136/bmj.k2179
9. Rogers, G. B., Keating, D. J., Young, R. L., Wong, M.-L., Licinio, J., & Wesselingh, S. (2016). From gut dysbiosis to altered brain function and mental illness: mechanisms and pathways. Molecular Psychiatry, 21(6), 738–748. doi:10.1038/mp.2016.50
10. Klinder, A., Shen, Q., Heppel, S., Lovegrove, J. A., Rowland, I., & Tuohy, K. M. (2016). Impact of increasing fruit and vegetables and flavonoid intake on the human gut microbiota. Food & Function, 7(4), 1788–1796. doi:10.1039/c5fo01096a
11. Solan, M. (2021, July 14). Want probiotics but dislike yogurt? Try these foods. Retrieved August 10, 2022, from Harvard Health website: https://www.health.harvard.edu/blog/want-probiotics-but-dislike-yogurt-try-these-foods-202107142545
12. Palmnäs, M. S. A., Cowan, T. E., Bomhof, M. R., Su, J., Reimer, R. A., Vogel, H. J., … Shearer, J. (2014). Low-dose aspartame consumption differentially affects gut microbiota-host metabolic interactions in the diet-induced obese rat. PloS One, 9(10), e109841. doi:10.1371/journal.pone.0109841
13. Madan, J. C., Hoen, A. G., Lundgren, S. N., Farzan, S. F., Cottingham, K. L., Morrison, H. G., … Karagas, M. R. (2016). Association of cesarean delivery and formula supplementation with the intestinal microbiome of 6-week-old infants. JAMA Pediatrics, 170(3), 212–219. doi:10.1001/jamapediatrics.2015.3732