What Are Probiotics? A Beginner’s Guide


The past decade has seen an enormous uptick in the use of probiotics—both supplementally and in food products. 

From soda and sparkling water to cookies to candy, hundreds of brands are now infusing their products with probiotics (which, by the way, does not automatically make them healthier).  

But what exactly are probiotics? And how do they impact health? Let’s find out.

What Are Probiotics?

The name probiotic means “for life,” indicating that probiotics are live microorganisms that benefit the host (AKA us).

As the trillions of bacteria in our guts constantly compete for space, adding probiotics to your diet or supplement regimen can help crowd out pathogenic and harmful gut bacteria.

Our large intestine (or colon) can house upwards of 100 trillion microbes comprising thousands of species ranging from harmful to neutral to beneficial. 

Coined as the “gut microbiome” back in 2001, this collection of microbes in our large intestines is now known to impact our health in both digestive and non-digestive ways.

Microbial diversity is essential because various bacterial species do different things, ranging from digesting fiber to producing vitamins and metabolites to modulating immune system function. 

When our gut microbiota populations become out of whack, dysbiosis—an imbalance of good and bad bacteria—can develop.

Dysbiosis is a common cause of health problems—both digestive and non-digestive—so repopulating your gut microbiome with friendly bacteria can help to correct this imbalance. 

As you’ll see, probiotics have a unique language, identified by their genus, species, subspecies, and alpha-numeric strain.

The most common genera found in probiotic supplements are lactic acid bacteria (like Lactobacillus, Bifidobacterium, Saccharomyces, Enterococcus, and Bacillus). 

For example, a commonly used probiotic is Bifidobacterium (genera) animalis (species) lactis (subspecies) DN-173 010 (strain). 

What Are Probiotics Used For? The Top Health Benefits

Probiotics have many potential health benefits, including treating or improving conditions ranging from irritable bowel syndrome and inflammatory bowel disease to acne and allergies.

What are probiotics used for?

IBS (Irritable Bowel Syndrome)

Irritable bowel syndrome is a widespread digestive condition with causes that are, unfortunately, not well understood. 

However, increasing amounts of evidence suggest that an unhealthy microbiome may be involved in its development and progression—and that probiotics may be able to help.

Several pro-inflammatory gut microbes (like Enterobacteriaceae) are found in people with IBS, and healthy bacteria (like Lactobacillus and Bifidobacterium) are lower.

Therefore, probiotics containing Lactobacillus and Bifidobacterium may be able to restore the balance of gut microbes and improve IBS symptoms. 

In a meta-analysis of 877 adults with IBS, those who took probiotics containing Bifidobacterium breve, Bifidobacterium longum, or Lactobacillus acidophilus had significant improvements in digestive pain scores compared to the placebo group.

Similarly, another meta-analysis combining data from 23 clinical trials found that probiotics reduced the risk of IBS symptoms by 21%. 

However, another review of 11 clinical trials concluded that only seven of them led to IBS improvement with probiotic supplementation, while four did not.

As irritable bowel syndrome is a highly individualized condition, probiotic supplementation may or may not work for everyone.

Leaky Gut

Also known as intestinal permeability, leaky gut is when the layer of epithelial cells lining the large intestine becomes “leaky” and has growing gaps between the cells.

When the intestinal lining becomes permeable, toxins, pathogens, and proteins can travel out of the gut into the bloodstream—which we do not want.

Although the research is not conclusive by any means, leaky gut may contribute to a range of health issues, including autoimmune disorders like type 1 diabetes, multiple sclerosis, rheumatoid arthritis, and celiac disease. 

Probiotics may be able to “close the gaps” in leaky gut. One small study found that multi-strain probiotics improved the intestinal barrier function by up to 48%.Another systematic review concluded that supplementing with the Lactobacillus genus of probiotics reduced gut permeability.


Small intestinal bacterial overgrowth (SIBO) is a digestive state where someone has excessive bacteria in the small intestine of their digestive tract. 

While it’s normal to have an abundance of bacteria in the large intestine, not many bacteria should be found in the small intestine, leading to painful and uncomfortable digestive symptoms when they are. 

In a study of 30 people with SIBO, those who took a probiotic containing Lactobacillus sporogenes in addition to a regular antibiotic course had a 93% clearance of SIBO, compared to 66% in the antibiotic control group.

The probiotic takers also had a complete remission of digestive symptoms like abdominal pain, gas, belching, and diarrhea.


Most people are familiar with what constipation is—and it’s no fun when it happens. 

Although a leading cause of constipation is not eating enough fiber, dysbiosis in the gut can also affect it.

In a 2020 meta-analysis, data from 15 clinical trials showed that probiotic consumption—especially probiotics containing multiple bacterial species—reduced gut transit time (how quickly food passes through the gut) by almost 14 hours.

Multi-species probiotics also increased the average stool frequency by 1.22 bowel movements per week.Similarly, two clinical trials reported that probiotics had a beneficial effect on chronic constipation, increasing the average number of stools per week by 1.49.


One of the first conditions that probiotics were found to treat successfully was diarrhea, including travelers’ diarrhea and antibiotic-associated diarrhea. 

Up to 30% of people who take antibiotics experience diarrhea because antibiotics kill off gut bacteria—both good and bad.

This microbial disturbance can alter things like fluid in the intestines, the number of pathogenic bacteria able to take hold in the gut, and intestinal motility, leading to an increased incidence of diarrhea. 

Research shows that probiotic supplementation reduces the risk of antibiotic-associated diarrhea by 51%. 

Certain probiotic strains may also reduce the risk of infectious diarrhea or pediatric diarrhea.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is comprised of two gastrointestinal disorders: ulcerative colitis and Crohn’s disease. 

While these diseases can be complex and multifactorial, one cause might be alterations to the gut microbiota. 

However, the available research so far has suggested that probiotic supplements may only benefit ulcerative colitis but not Crohn’s disease. 

In a 2020 review of 14 studies and 865 people with ulcerative colitis, the researchers concluded that probiotic supplements combined with an IBD medication were able to induce remission more than the IBD medication alone. 

However, most of the studies were small, and more research is needed to determine which cases of IBD might benefit from probiotics the most—and which probiotic strains are the most effective.

Non-Digestive Conditions

Probiotics are even thought to have health benefits for non-digestive conditions, including:

What Foods Have Probiotics?

Probiotic-rich foods are all forms of fermented foods, including: 

  • Sauerkraut
  • Kimchi
  • Fermented dairy products (like kefir, yogurt, buttermilk, and sour cream)
  • “Real” pickles (refrigerated ones) 
  • Fermented vegetables 
  • Kombucha 
  • Tempeh
  • “Real” sourdough (does not contain yeast or preservatives)
  • Miso
  • Natto

What Are the Best Probiotic Supplements?

With all of the different species, strains, and genus names, It is understandably confusing to pick out probiotic supplements.

Although it can be best to get your probiotics from fermented foods (one tablespoon of sauerkraut juice contains 1.5 trillion CFUs of probiotics!), many people don’t enjoy the sour or “funky” taste of many probiotic-rich foods (you should give them a try, though!).

If you don’t want to eat your probiotics, some of the best probiotic supplements can be found in these articles: Best Probiotics for Men and Best Probiotics for Women.

Briefly, here are a few of our top favorites for women: 

  • WiseHuman Women’s Daily Probiotic: With 20 billion CFUs (colony-forming units) of probiotics and prebiotics, this supplement is designed to support digestive, vaginal, and immune system health.
  • Garden of Life Dr. Formulated Once Daily Probiotic: This probiotic supplement has 50 billion CFUs of beneficial bacteria made up of 16 probiotics, including Lactobacillus reuteri and Lactobacillus fermentum, two documented probiotic species for women’s health. 
  • Nordic Naturals Flora Probiotic Daily: This supplement contains 12 billion CFUs, including the first commercialized probiotic for dietary supplements, Lactobacillus acidophilus DDS-1, combined with the prebiotic fiber FOS (fructooligosaccharide) to support healthy gut bacteria growth. 

For men looking for a probiotic, try one of these:

What Are Probiotics FAQs

What Do Probiotics Actually Do?

There are many potential health benefits of probiotics, as these beneficial bacteria can repopulate the gut and reduce dysbiosis—a buildup of “bad” bacteria without enough good bacteria.

Although it can vary individually, research has shown that probiotic supplements may benefit digestive health, including disorders like irritable bowel syndrome (IBS), inflammatory bowel disease (IBD, which includes ulcerative colitis and Crohn’s disease), SIBO (small intestinal bacterial overgrowth), constipation, and diarrhea.

Probiotics may also have health benefits for symptoms or conditions not related to gut health, including inflammatory skin conditions (acne, eczema/atopic dermatitis, and psoriasis), allergies, obesity, and depression.

What Are Live Probiotics?

All probiotics need to be alive to exert any effects. If a probiotic supplement does not contain live microorganisms, the bacteria cannot populate your gut. Our harsh stomach acidity can kill off many friendly microbes before they reach the large intestine.

Therefore, unique delayed-release supplement delivery systems can bypass the stomach and release the beneficial bacteria at the right place and time. High-quality probiotic supplement brands will undergo testing to ensure the probiotics are still alive once they reach the gut.

How Do You Know If You Need Probiotic Supplements?

There are many potential signs that you could consider probiotic supplements, including any digestive health-related issues, poor immune system or getting sick constantly, mental health disorders, inflammatory skin issues, and frequent urinary tract infections, yeast infections, or vaginal infections.

What Are Probiotics’ Downsides?

Some people might experience digestive discomfort when starting a probiotic, especially if it has a large number of strains or a high CFU count. However, the potential gut health benefits over time typically outweigh the possible discomfort initially.

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