What Are Probiotics?

Probiotic Food and Supplement

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Probiotics are a combination of live bacteria and yeasts which people consume in foods or supplements in hopes of gaining health benefits. We about 30 to 40 trillion bacteria naturally living inside of us, and probiotics work by influencing that population of bacteria.

When you think of bacteria, it's easy to immediately associate it with conditions like acne or more serious diseases. However, there are good and bad forms of bacteria. Probiotics are similar to the bacteria that live naturally in your body and may help to fight off bad bacteria that can negatively affect your health.

As an organism within your body, probiotics make up what is known as the microbiome—a community of microorganisms like fungi, viruses, protozoa, and, as we’ve seen, bacteria. The microbiome is important for maintaining immunity, improving digestive health, and preventing heart disease. Probiotics may be found in the gut, mouth, vagina, urinary tract, skin, and lungs.

Strains of Probiotics

Probiotics are named by identifying the genus, species, and strain.

For example, let's look at Bifidobacterium lactis HN019.

  • HN019 signifies the strain, or the simplest level of identification, which can be thought of like an individual family member.
  • Lactis is the species or the larger immediate family of the bacteria.
  • Bifidobacterium is the genus or the strain's extended family.

Each strain has specialized benefits for the health. There are many types of strains, but seven main genera (plural of genus, or the strain's larger family) of probiotics typically found in probiotic supplements. These include:

  • Lactobacillus
  • Bifidobacterium
  • Saccharomyces
  • Streptococcus
  • Enterococcus
  • Escherichia
  • Bacillus

As we noted, probiotics are also found in yeasts. Common probiotic yeast strains include Saccharomyces cerevisiae var. Boulardii, Metschnikowia ziziphicola, and Saccharomyces cerevisiae.

Sources of Probiotics

Many people take probiotic supplements in the form of capsules or powder. However, probiotics are naturally found in fermented foods.

Food sources that contain probiotics include:

  • Yogurt
  • Cheese
  • Japanese miso
  • Sauerkraut
  • Kefir
  • Kombucha
  • Sourdough
  • Kimchi
  • Olives
  • Pickles
  • Fermented soy foods like tempeh

Probiotic strains have also been found in non-fermented foods like:

  • Cereals
  • Legumes
  • Cabbage
  • Maize
  • Sorghum

These foods also contain prebiotics. Prebiotics are the "food" for probiotics. They help probiotics thrive and populate and in addition to helping to improve gastrointestinal health, they may also potentially enhance calcium absorption.

Probiotics may also be found in interesting places like the foremilk (colostrum) of breastmilk and your gastrointestinal tract. It is also present in animal gut—pigs, rats, some marine/freshwater fish, as well as certain poultry have probiotics lurking in their insides.

Characteristics of Probiotics

For microbiomes to be counted as probiotics, they have to possess the following characteristics:

  • Durability in harsh conditions: Probiotics must be able to power through low pH levels in the stomach or gastric juices.
  • Survival in the intestine after digestion: This will require resistance to bile acid, as well as stomach acid.
  • Antimicrobial activities: Probiotics should be able to fight against microbes like fungi and even bacteria.
  • Isolation from different sources: Probiotics used by humans are popularly isolated from dairy or non-dairy sources such as fermented foods. However, they may also be isolated from the human body for our use.
  • Safe for consumption: Probiotics must be deemed safe for humans to consume in foods or take as supplements.

How Do Probiotics Work?

Unfortunately, it isn’t exactly certain how probiotics perform their role in the body. They may help boost the body’s immunity against dangerous outsiders. They may also work to make sure the body gets better at fending off these invaders.

In addition to immunity, probiotics perform anti-inflammatory roles within the body. Claims have also been made that probiotics may help with managing the body’s response to pain.

Probiotic Supplements

Probiotic supplements are widely used. In fact, a 2012 National Health Interview Survey found that about four million American adults had used probiotics within a recorded month.

It's important to note that while probiotics are commonly consumed as dietary supplements, they are also found in foods such as yogurt and kimchi and may also be ingredients in pharmaceuticals.

Each of us has a unique population of different types of bacteria living inside of us, and it is not necessary to consume probiotic foods or supplements to maintain that population. In fact, you can focus on increasing your consumption of whole plant foods to help improve the health of your gut.

Benefits of Probiotics

Research in the area of probiotics is still relatively inconclusive. There are many different types of probiotics, and, while there is some promising research, it takes time to determine which strains may benefit which conditions and which conditions may not benefit at all. Probiotics may have the following beneficial effects on the body:

Regulate the Body’s Immune Response

Probiotics regulate the body's immune response in different ways.

Probiotics can encourage the activities of antibodies like T cells and stop bad bacteria in their tracks by preventing them from accessing the intestine's protective covering or barrier. They also enhance the protection offered by the intestine's covering and stimulate an anti-inflammatory response when the body is confronted by dangerous outsiders. However, more research needs to be done to determine which probiotic strains may benefit the immune system.

Improve Symptoms of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a disorder of the intestine that can cause diarrhea, cramps, gas, and constipation. While it's a little hard to pinpoint what causes this condition, links have been drawn to food sensitivity, brain-gut interactions, as well as bacterial overgrowth.

Probiotics may work by protecting against harmful, IBS-causing bacteria through their bacteria-fighting properties. They may also support the intestinal barrier to prevent attacks by dangerous outsiders. Some studies show that probiotics may help to normalize bowel movements in people living with IBS.

However, each of these studies show benefits of supplementing with a particular strain in just one trial. There needs to be more rigorous research, where each strain is studied in multiple high quality trials to determine which probiotic strains may benefit IBS patients.

Other treatments, including dietary interventions such as a low FODMAP diet or psychological interventions such as gut-focused hypnotherapy have been shown to be effective treatment strategies for managing IBS.

Reduce Atopic Dermatitis in Children

Certain probiotics may help manage the appearance of atopic dermatitis (an itchy skin inflammation that usually affects children) depending on the severity of the condition, and may also provide prenatal support to prevent the baby from contracting this condition.

Research is still preliminary, but early trials show that the topical application (applied to the skin instead of consumed) of the naturally-occurring skin bacteria Roseomonas mucosa may decrease the severity of the disease, decrease the amount of the bacteria contributing to the inflammation, and reduce the need for topical steroids. The coming years will bring more trials and hopefully more guidance on this approach.

Oral probiotics may also be beneficial because of their effects on the intestinal barrier which in turn helps reduce the severity of the condition. However, optimal dosage, timing, and type of probiotic have yet to be determined.

Help Manage Antibiotic-Induced Diarrhea

Taking antibiotics to manage or prevent bacterial infections can sometimes lead to diarrhea. This occurs because antibiotics tend to disturb the microbiomes in the intestine, which can cause excessive fluid to build up. The intestinal fluid build-up encourages diarrhea, and the disruption of the microbiome may also increase the risk of infections from other disease-causing organisms.

Three probiotic strains are able to reduce the chances of antibiotic-associated diarrhea, Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus rhamnosus. This applies to patients of all ages, especially those above 65 who are at a higher risk of developing this condition.

Help Prevent Pouchitis

Some people with Inflammatory Bowel Diseases (IBD) need to have surgery to remove their colon and rectum. Something called a J-pouch is formed, which creates a new structure to store and pass stool. This procedure may increase your risk of an infection known as pouchitis.

The American Gastroenterological Association (AGA) recommends an 8 strain probiotic which may help prevent pouchitis in up to 90% of individuals who have undergone J-pouch surgery, though if the probiotic is too expensive, it is not necessary.

Side Effects of Probiotics

Despite the many potential benefits of probiotics, the jury is still out on just how safe probiotic supplements are. There have been rare reports of fungemia (a condition that leads to the presence of yeast or fungi in the blood) and bacteremia (the presence of bacteria in the blood). Probiotic use may also be linked with an inflammation of the tissue lining the heart.

You also want to be careful with using probiotics if you're suffering from a serious illness, have recently had surgery, or are currently experiencing a compromised immune system.

Note that probiotics can be marketed as a dietary supplement, a drug, or a food ingredient. Most probiotics are sold as dietary supplements, which are not regulated by the Food and Drug Administration (FDA), so you may want to take a closer look at the product before taking it.

Always consult with a health care practitioner before adding a supplement, such as probiotics, to your routine. Different strains of probiotics have different functions in the body so the type you need may depend on what you are using it for.


Many foods that contain probiotics also contain prebiotics. Prebiotics are the "food" for probiotics. They help probiotics thrive and populate and in addition to helping to improve gastrointestinal health, they may also potentially enhance calcium absorption. Prebiotics are found in food such as such as bananas, onions, garlic, leeks, asparagus, artichokes, beans and whole-grain foods.

While easy to mix up, probiotics are not to be mistaken for prebiotics found in these plant foods. Prebiotics are certain types of fiber that serve as food for your naturally occurring gut bacteria. You can get prebiotics from eating fruits, vegetables, and whole grains, and eating more of these foods is beneficial for the health of your digestive system in a number of different ways.

If you do decide to supplement with a probiotic to address a particular health concern, it's a good idea to do so under the supervision of a registered dietitian or medical practitioner.

A Word From Verywell

Probiotics are potentially beneficial bacteria that you may or may not benefit from. Beneficial bacteria help maintain gut health, are useful for maintaining immunity, and may even offer protection against certain skin diseases. However, there is still much research to be done to determine the best strains and dosages of probiotic supplements for particular health conditions.

Probiotics exist in fermented foods and is naturally present in specific parts of the body. Before supplementing, discuss your needs with a healthcare provider or registered dietitian.

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Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Elizabeth Plumptre
Elizabeth is a freelance health and wellness writer. She helps brands craft factual, yet relatable content that resonates with diverse audiences.