What are Probiotics?

What are Probiotics?

by Zach Bendiks

If you go to the grocery store or watch health and fitness YouTube videos long enough, you may come across the word “probiotic”. You’ve probably seen that word before and know that it’s good for you, like how “vitamins” and “antioxidants” are good for you. The past two decades have seen a dramatic increase in research and public interest in probiotics and how they can be used to improve health, and the worldwide probiotics market is fast approaching $50 billion. They can be found in pills and other supplements or they can be present in fermented foods such as kombucha, sauerkraut, kimchi, and other fermented fruits and vegetables. There are even probiotic skincare products and probiotics for pets! But do you know what probiotics are and how they work? In this article, we will explore how probiotics interact with the human body and discuss some of the well-known probiotics available.

Probiotics are defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP) as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” (Hill et al. 2014). These microorganisms, usually bacteria, are consumed alive so they interact with the body and, in turn, improve our health in some way. This is different from “prebiotics”, another term you may have seen, which are certain carbohydrates that are consumed by the gut microbiome but do not contain living microbes (for more discussion of the microbiome, see my previous post). In addition, some people have combined probiotic bacteria with prebiotic carbohydrates with the idea that the carbohydrate will serve as a food source for the bacteria as it travels through the small and large intestines. This combination is referred to as a “synbiotic”. The differences between these three terms in highlighted in Figure 1.

But how do probiotics work? There are many different ways these microbes can interact with the human body, depending on the strain used (Plaza-Diaz et al. 2019). These basic mechanisms are illustrated in Figure 2, which focuses on the gut since most probiotics are eaten and then pass through the intestines. Probiotics can colonize the human gut and prevent harmful bacteria from doing the same, which helps restore balance to the microbiome. Probiotics produce small molecules like short chain fatty acids (SCFA) that have several important functions throughout the body, like providing energy for cells in the colon. They can convert bile acids in the gut, which has cholesterol-lowering effects, and produce proteins such as bacteriocins that interact with host cells and have anti-bacterial effects. Probiotics adhere to the gut lining and alter immune responses, leading to decreased inflammation, increased immune regulation, and tighter connections between gut cells. Finally, increases in SCFA levels can enhance the production of serotonin precursors which could affect mood, cognition, and your sense of well-being. While more work is needed to understand the relationship between gut bacteria and the brain, the “gut-brain axis” is an exciting new area of research (Kim et al. 2018).

Many bacteria commonly studied and marketed as probiotics come from the Lactobacillus and Bifidobacterium genera, though numerous others are also being investigated for their health-beneficial properties. Different strains of bacteria, even from the same genus or species, can have very different effects on the body so the impact of one strain cannot be generalized to others. Lactobacillus is a diverse group of bacteria that is found in many different environments including food fermentations and the human vaginal microbiome. One well-known probiotic from this genus is L. rhamnosus GG, which has been shown to prevent digestive issues in children (Szajewska et al. 2019) and is one of the most studied and widely available probiotics out there. Bifidobacterium are members of the human gut microbiome and play an important role in development and microbiome function. One promising study showed that the probiotic B. longum NCC3001 reduced symptoms of depression and altered brain activity in patients with irritable bowel syndrome, though surprisingly it did not improve measurements of gut function and health (Pinto-Sanchez et al. 2017). These two genera make up the bulk of probiotics available on the market, and dozens of different Lactobacillus and Bifidobacterium strains are sold either together or individually as probiotic supplements. However, many probiotic products use strains of bacteria that are not native to the gut microbiome. This means the strains are not adapted to the gut environment and may struggle to survive and promote health-beneficial effects. There has been increased interest in “next generation probiotics” that use bacteria native to the human gut, including strains of Faecalibacterium prausnitzii and Akkermansia muciniphila (Satokari 2019). F. prausnitzii is one of the most abundant microbes in the human gut and decreases in F. prausnitzii levels have been associated with inflammatory bowel disease and diabetes development (Ganesan et al. 2018). In total, there are hundreds of different bacteria that have been examined and used for their probiotic potential, and more will become available as research discovers new strains that can improve health.

Despite the potential of probiotics, there are important caveats to keep in mind. ISAPP stresses that only strains which have been tested in controlled clinical settings and have demonstrated health benefits should receive the ‘probiotic’ label, but government regulation has lagged in this area. Probiotics can be marketed as dietary supplements which do not require approval from the Food and Drug Administration, and many probiotics on the market do not list the strain(s) used in the product which makes it impossible to know whether the bacteria present have been tested (Probiotics: What You Need To Know 2019). Furthermore, in young children and severely immunocompromised individuals, probiotics can escape the gut environment and enter the bloodstream, a condition known as bacteremia, which could lead to health problems (Kulkarni 2019). Even with these challenges, probiotics show a lot of promise for improving human health, and the usefulness of probiotics will only increase over time as scientists identify and test new strains, legislators improve the regulatory framework around probiotics, and the public becomes more informed about the benefits and drawbacks of individual strains.   

References

Ganesan, Kumar, Sookja Kim Chung, Jairam Vanamala, and Baojun Xu. 2018. “Causal Relationship between Diet-Induced Gut Microbiota Changes and Diabetes: A Novel Strategy to Transplant Faecalibacterium Prausnitzii in Preventing Diabetes.” International Journal of Molecular Sciences.

Hill, Colin et al. 2014. “Expert Consensus Document: The International Scientific Association for Probiotics and Prebiotics Consensus Statement on the Scope and Appropriate Use of the Term Probiotic.” Nature Reviews Gastroenterology and Hepatology.

Kim, Namhee, Misun Yun, Young Joon Oh, and Hak Jong Choi. 2018. “Mind-Altering with the Gut: Modulation of the Gut-Brain Axis with Probiotics.” Journal of Microbiology.

Kulkarni, Rajan P. 2019. “Probiotics Leap from Gut to Blood.” Science Translational Medicine.

Pinto-Sanchez, Maria Ines et al. 2017. “Probiotic Bifidobacterium Longum NCC3001 Reduces Depression Scores and Alters Brain Activity: A Pilot Study in Patients With Irritable Bowel Syndrome.” Gastroenterology.

Plaza-Diaz, Julio, Francisco Javier Ruiz-Ojeda, Mercedes Gil-Campos, and Angel Gil. 2019. “Mechanisms of Action of Probiotics.” In Advances in Nutrition,.

“Probiotics: What You Need To Know.” 2019. Health, National Center for Complementary and Integrative, National Institute of Health. https://www.nccih.nih.gov/health/probiotics-what-you-need-to-know.

Satokari, Reetta. 2019. “Modulation of Gut Microbiota for Health by Current and Next-Generation Probiotics.” Nutrients.

Szajewska, Hania et al. 2019. “Systematic Review with Meta-Analysis: Lactobacillus Rhamnosus GG for Treating Acute Gastroenteritis in Children – a 2019 Update.” Alimentary Pharmacology and Therapeutics.