Article by Kyla Trkulja

Graphic design by Sherry An

The human microbiome is estimated to contain about 100 trillion bacteria consisting of over 1000 species.¹ Over the past few decades, the importance of this group of organisms has become abundantly clear, as these microbes act as their own organ system with many metabolic, immunological, and endocrine-like functions that influence human health.² For example, microbes in the gut synthesize vitamins, amino acids, and important metabolic byproducts for the human host.³ These include vitamin K for blood clotting and short chain fatty acids (SCFAs) for energy.³ Other benefits include the breakdown of dietary toxins, nutrients, and carcinogens, conversion of cholesterol into other essential fats, assisting in the maturation of the immune system, and protecting humans from harmful bacteria that could otherwise invade the gut.² This wide variety of health benefits is due to the gut microbiota consisting of organisms that have specialized enzymes and abilities that differ from us humans, allowing them to live in our bodies and thrive without causing us harm while actually promoting health and preventing disease.

How Does the Microbiome Influence Health?

An imbalance in the microbiome, known as dysbiosis, has been associated with immune disorders, susceptibility to infections, and pathologies such as cardiovascular disease, obesity, diabetes, liver and brain disease, autism, and mood disorders.^2,3 Various studies have examined the composition of the gut microbiome and its associations with conditions including inflammatory bowel disease (IBD), inflammatory skin diseases such as psoriasis and dermatitis, arthritis, diabetes, obesity, and atherosclerosis.³ In addition, recent research has found that our lifestyle and diet choices influence the microbiome of the gut; for example, high intake of red meat increases the abundance of bacteria that produce trimethylamine-N-oxide (TMAO), a compound that increases the risk of cardiovascular disease.³ Findings such as these have demonstrated that we as humans have the ability to influence our own microbiomes, which can improve our health if done strategically.

Manipulating the Microbiome with Probiotics

Various foods such as cultured milk products and yogurts contain lactic acid bacteria, a source of consumable microbes that can promote a healthy gut microbiome.³ Commonly referred to as “probiotics”, these foods enriched in beneficial bacteria can have a positive impact on our health. In fact, companies even sell probiotic supplements that can be taken as capsules, tablets, packets, or powders so the benefits can be obtained without necessarily consuming the appropriate foods.⁴ The most widely used probiotics are the beneficial Lactobacillus and Bifidobacterium groups, which may have health benefits such as reducing body fat mass, improving glucose and lipid balance, and regulating the immune system.^{2, 4-5}

Some of the health benefits of probiotics have been validated through randomized controlled trials and extensive research, but others are only supported by inconsistent evidence.⁴ There is strong evidence supporting the use of probiotics to improve stool consistency, regulate bowel movements, reduce abdominal bloating, prevent vaginal, E. coli, and H. pylori infections, and reduce the incidence and symptoms of the common cold.⁶ Other less supported benefits may include improvement of mood, reduction of depression and anxiety symptoms, weight loss, and balancing of metabolic markers of health such as cholesterol and pro-inflammatory cytokines.^{2-3, 5-6} Furthermore, probiotics have been found to potentially aid in weight loss and have maximum health benefits when combined with diet and exercise. This is due to the bacteria breaking down metabolic byproducts like fermented proteins that are produced when exercising.⁷ Future research will hopefully be able to decipher which benefits are reliable, but even with our limited knowledge, the potential pros of consuming probiotics outweigh the cons.

Nonetheless, it is important to note a few other considerations before taking probiotics. Most importantly, everyone’s body is different, and their age, gender, co-morbidities, genetics, and body environment may result in a different outcome when taking probiotics; as a result, probiotics might not benefit everyone, and may even be harmful for some.^1,8 Similarly, since probiotics contain live microorganisms, there is the risk of infections, side effects, and complications in some individuals.^1,4 Those who are most at risk are immunocompromised individuals or people with immunological disorders; however, everyone should talk to their doctor before taking probiotic supplements, just like they would with any medication.⁸

The gut microbiota also depends on other factors such as genetics and diet; therefore, taking probiotic supplements will not result in benefits without taking this into consideration.⁶ Finally, it’s important to remember that the gut microbiome can change quickly, returning back to baseline within 1-3 weeks after ceasing probiotics.⁶ This emphasizes the fact that probiotics should be combined with a healthy lifestyle for maximum benefits, and that they are not a permanent solution to wellness.

However, despite the considerations, probiotics are generally considered a safe, accessible, and well-tolerated way to balance the gut microbiome and improve health. Talk to your doctor to determine which type of probiotics you should take, since they aren’t all created equal, and combine them with healthy living to let you and your microbiome thrive.

References

1. Lordan, C., Thapa, D., Ross, R. P., et al (2020) Potential for enriching next-generation health-promoting gut bacteria through prebiotics and other dietary components. Gut Microbes, 11:1, 1-20, DOI: 10.1080/19490976.2019.1613124
2. Gérard, P. (2016) Gut microbiota and obesity. Cellular and Molecular Life Sciences, 73, 147–162. https://doi-org/10.1007/s00018-015-2061-5
3. Singh, R.K., Chang, HW., Yan, D. et al. (2017) Influence of diet on the gut microbiome and implications for human health. Journal of Translational Medicine, 15, 73. https://doi.org/10.1186/s12967-017-1175-y
4. Williams, N. T. (2010) Probiotics. American Journal of Health-System Pharmacy, 67(6), 449–458. https://doi.org/10.2146/ajhp090168
5. Mueller, M., Ganesh, R. & Bonnes, S. (2020) Gut Health = Mental Health? The Impact of Diet and Dietary Supplements on Mood Disorders. Current Nutrition Reports, 9, 361–368. https://doi.org/10.1007/s13668-020-00340-2
6. Khalesi, S., Bellissimo, N., Vandelanotte, C. et al. (2019) A review of probiotic supplementation in healthy adults: helpful or hype? European Journal of Clinical Nutrition, 73,24–37. https://doi.org/10.1038/s41430-018-0135-9
7. Sergeev, I. N., Aljutaily, T., Walton, G., et al (2020) Effects of Synbiotic Supplement on Human Gut Microbiota, Body Composition and Weight Loss in Obesity. Nutrients, 12(1), 222. https://doi.org/10.3390/nu12010222
8. Kothari, D., Patel, S., Kim, S. K. (2019) Probiotic supplements might not be universally-effective and safe: A review. Biomedical Pharmacotherapy, 111, 537-547. doi: 10.1016/j.biopha.2018.12.104.
9. Ruan W, Engevik MA, Spinler JK, et al. (2020) Healthy Human Gastrointestinal Microbiome: Composition and Function After a Decade of Exploration. Dig Dis Sci 65, 695–705. https://doi.org/10.1007/s10620-020-06118-4
10. Daliri EB, Ofosu FK, Xiuqin C, et al. (2021) Probiotic Effector Compounds: Current Knowledge and Future Perspectives. Front Microbiol, 12:655705. https://doi.org/10.3389/fmicb.2021.655705.