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What’s the Point of Probiotics?

When I was in grad school (for poetry, obviously), I had a roommate who supplemented with probiotics. At that point, I didn’t know what a probiotic was or why I would need one. She told me it was to help with digestion. “Oh,” I said. “Do you have digestive problems?”

“No,” she responded.

“Then why take them?” I wondered.

“To help with digestion.” It was like an Abbott and Costello skit. She only knew that she was supposed to take probiotics to help with digestion and I didn’t understand why she needed help with digestion if she was digesting food fine. I think we both missed the point. To understand why you might want to supplement with probiotics, first you have to understand what they’re really for.

If you’re not interested in the science of probiotics, scroll down to the section labeled “How do Probiotics Help?”

Meet Your Microbiota

Our guts are made up of human cells and also an insane amount of bacteria. Billions of bacteria, swarming around, doing what bacteria do all the while being invisible to the naked eye. Colonizing. Eating. Don’t think about it for too long or your face will do this:

These billions of bacteria work with us and for us in a symbiotic relationship. They help us digest food (including dietary fiber), they can make Vitamin K, and they attack pathogens. These helpful bacteria are often referred to in scientific literature as “commensal bacteria,” meaning that they derive benefit from living off of us and they don’t hurt us. However, it seems clear to me (and to Gut Microbiota for Health) that these bacteria actually help us just as we help them by providing “a nutrient-rich environment,” making it a mutualistic symbiotic relationship rather than simply a commensal one.

When our gut bacteria (also known as microbiota) are in balance, we are digesting well and we are also less likely to get sick. However, when our gut bacteria is out of balance, instead of symbiosis, we have dysbiosis. According to Dr. Mary Ellen Sanders in a 2011 article published in the Journal of Clinical Gastroenterology, “there are numerous diseased states associated with a disturbed gut microbiota…. In most cases, it is not known if the disturbed microbiota is causal or correlative...but the fact that the disturbed microbiota may play a role in the onset or development of certain diseases leads to the hypothesis that interventions that can return the microbiota to a healthier state may mitigate the disease. Administration of properly selected probiotics may be such an intervention.”

So when I asked my roommate why she was using probiotics and she answered “to help with digestion,” she was missing the larger purpose. Sure, probiotics can help with digestion, but the real goal is to restore or improve the diversity and balance of your helpful gut bacteria. As Sanders said, we don’t know if having a “disturbed microbiota is causal or correlative,” meaning it is unclear whether having bacterial dysbiosis causes illnesses or whether dysbiosis and illness simply seem to occur together — it is possible that these illnesses affect your gut microbiota at the same time as they affect you. Illnesses that Sanders lists as being affected by (or that occur in conjunction with) an unhealthy microbiota include digestion issues like celiac, inflammatory bowel disease, and irritable bowel syndrome, as well as non-digestion related illnesses like asthma, types 1 and 2 diabetes, and rheumatoid arthritis.

Without getting too much into the science of it all, let’s assume that Sánchez et al. are correct in their 2017 article when they attribute the following tasks to microbiota (I added the text in parenthesis to help with clarification, the rest is quoted directly from the article):

  1. Maintenance of the epithelial barrier (the epithelial barrier refers to a layer of cells that separates you from things that are not you, like food or bacteria)

  2. Inhibition of pathogen adhesion to intestinal surfaces (i.e. not letting other bacteria set up shop in your body)

  3. Modulation and proper maturation of the immune system (i.e. mice raised germ-free were found to have less robust immune keep eating dirt, kids)

  4. Degradation of otherwise nondigestible carbon sources such as plant polysaccharides (as mentioned above, helping you digest things like insoluble fiber)

  5. Production of different metabolites such as vitamins and SCFAs (also mentioned above, helping you create vitamins and short-chain fatty acids)

How do probiotics help?

According to Sánchez et al., “Probiotics exert their beneficial effects on the host through four main mechanisms: interference with potential pathogens, improvement of barrier function, immunomodulation and production of neurotransmitters, and their host targets vary from the resident microbiota to cellular components of the gut–brain axis.”

If you compare those mechanisms to microbiota jobs listed above, you’ll notice a lot of similarities. It follows that at the most basic level, the goal of a probiotic supplement is to help your body’s microbiota do its job. A probiotic supplement adds diverse live bacterial strains to your microbiota. Each strain has a specific job to do, whether it’s to help fight off unhelpful bacteria, to synthesize various chemicals, or keep your guts from leaking.

Shall we make that face once more, with feeling?

The following health concerns have been associated with having low microbial diversity:

  • Infectious Diarrhea

  • Antibiotic-Associated Diarrhea

  • Inflammatory Bowel Disease

  • Irritable Bowel Syndrome

  • H pylori Infection

  • Lactose Intolerance

  • Metabolic Disorders and Obesity

  • Non-Alcoholic Fatty Liver Disease

  • Heart Disease

Above I quoted Sanders as saying that we don’t know yet if a lack of bacterial diversity causes these illnesses or simply occurs alongside them. The list above is not exhaustive, but I only included health concerns for which I was able to find research to support the use of probiotics in combating them. As Sanders points out, there is more research to be done, especially in terms of which strains specifically effect which issues.

If the health concerns above (and other issues associated with a lack of diversity in the microbiome, like allergies and asthma) are actually caused by the lack of diversity in the microbiome, then it is possible that taking probiotics will help the user avoid some of these issues. In that case, probiotics can be used by anyone as a preventative rather than only by someone seeking relief.

What’s the hullaballoo?

Some foods that are labeled probiotic are not. According to Quigley, some foods labeled as probiotic don’t have the strains of bacteria they claim, the bacteria are dead (research shows they have more effect when they’re alive) because of production or storage issues, the bacteria included have yet to demonstrate a commensal effect on humans, and the foods sometimes contain bacteria they’re not supposed to have.

In addition, taking a probiotic supplement doesn’t seem to change your microbiome in the long term. Some of the beneficial bacteria that are found in probiotics and that are thought to have the most affect mitigating the issues listed above do not colonize the body. This means that when you stop taking a probiotic supplement, you will eventually...well...poop all those bacteria out. So, taking probiotics would be more akin to taking a multivitamin (daily and continuous) than an ibuprofen (taken for an acute issue).

So how do I get the good stuff?

Always talk to your doctor before starting a new supplement, especially if you have issues that might be exacerbated by such a supplement. There have been instances of death in patients with acute pancreatitis who were administered probiotics nasally.

When choosing a probiotic, look for one with lots of different bacterial strains listed in the ingredients. Two strains that have been found to be especially helpful include Lactobacillus and Bifidobacteria. Precision Nutrition recommends supplementing with 3-5 billion bacteria per day, and increasing that dose to up to 10 billion if you’re trying to ameliorate a specific health concern.

To increase the chances you’re getting live bacteria, only purchase probiotics that are refrigerated rather than just picking something up off a shelf. And, just as I recommended in my article on fish/algae oils [[insert link]], check a reputable third-party reviewer like Labdoor. They have an entire section on probiotics, which discusses whether the brand met the claims on it’s label for viable bacteria as well as product purity, nutritional value, ingredient safety, and projected efficacy.


Falcinelli, S., Rodiles, A., Hatef, A., Picchietti, S., Cossignani, L., Merrifield, D., Unniappan, S., & Carnevali, O. (2018). Influence of Probiotics Administration on Gut Microbiota Core. Journal of Clinical Gastroenterology, PublishAheadofPrint,

Quigley, E. (2011). Gut microbiota and the role of probiotics in therapy. Current Opinion in Pharmacology, 11(6), 593-603.

Sánchez, B., Delgado, S., Blanco‐Míguez, A., Lourenço, A., Gueimonde, M., & Margolles, A. (2017). Probiotics, gut microbiota, and their influence on host health and disease. Molecular Nutrition & Food Research, 61(1), n/a-n/a.

Sanders, M. (2011). Impact of Probiotics on Colonizing Microbiota of the Gut. Journal of Clinical Gastroenterology, 45,

White, N. (2016). Gut Microbiota and Obesity. American Journal of Lifestyle Medicine, 10(2), 104-106.

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