Evidence Based Research
Our editorial team is made up of expert registered dietitians with extensive, real-world clinical experience who are highly trained in evaluating clinical research.
Read Our Editorial Policy

Probiotics 101: A Practical Beginner’s Guide

By Markita Lewis, MS, RD

Medically Reviewed by Anthony Dugarte, MD

Published on December 15, 2021

When it comes to probiotics, not all bacteria are bad. We discuss what microorganisms count as probiotics, their health benefits, and how to choose the best probiotic for you.

Written by
Markita Lewis, MS, RD
Registered Dietitian Nutritionist
Markita Lewis is a registered dietitian with over 5 years of experience in the field of nutrition and health. Prior to her professional career, Markita completed a combined masters and dietetic internship program at the University of Georgia. She obtained her undergraduate degree at Louisiana State University in Nutrition and Foods Sciences, concentrating in dietetics with a minor in Psychology.
Medically Reviewed by
Anthony Dugarte, MD
Medical Reviewer
Anthony Dugarte, M.D., C.S.C.S. is a health and wellness writer and medical content reviewer. In addition to dedicating the last 7 years to medical research, Dr. Dugarte also has more than a decade of experience in strength and conditioning, nutrition, and rehabilitative exercise, as well as authoring and reviewing health and wellness-related content.
Probiotics 101: A Practical Beginner’s Guide
Photo credit: iStock.com/kupicoo

What Are Probiotics?

The word probiotic comes up quite frequently when people are talking about health, but not many people know what they are.

According to a consensus made by the International Science Association for Probiotics and Prebiotics, probiotics are “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” (1)

In other words, probiotics are certain bacteria and yeasts that can benefit your health when you take a certain amount of them at one time.

Probiotic Names and Why They Matter

Probiotics users should know that not all bacteria and yeasts have the same actions on the body. The benefits of probiotics are specific, even down to the individual strain.

What do I mean by this?

Well, microorganisms are named by the taxonomic system that names all living organisms, such as Homo sapiens (aka, people).

The names of microorganisms are often described as the three lowest levels of the taxonomy – the genus, species (and subspecies), and strain (the most specific typing you can get).

The microorganisms that are primarily used in probiotics are from 6 different genera of bacteria:

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

Out of these, probiotic supplements are more frequently made with Lactobacillus and Bifidobacterium bacteria.

A difference in strain may impact the condition that the probiotic affects, so you have to pay attention to all parts of the name.

For example, you may have a bacteria called Bifidobacterium longum R0175 and another called Bifidobacterium longum BB536. They seem to be very similar, with the exception of a few letters and numbers (the strain), but their effects differ greatly.

Research suggests that Bifidobacterium longum R0175 may be effective for improving feelings of anxiety, while Bifidobacterium longum BB536 may be beneficial for allergic rhinitis and asthma. (2, 3)

As you can see, the strain makes a difference.

There is less research on the use of yeasts for probiotics, but the yeast Saccharomyces boulardii is found in studies to be an effective probiotic. (4)

How Do Probiotics Differ from Prebiotics?

The words “probiotic” and “prebiotic” are a tricky pair, just like the pair of words “stalagmite” and “stalactite.”

Put simply, probiotics are good bacteria, and prebiotics are the foods that feed those good bacteria.

Prebiotics are food components that humans aren’t able to digest normally. These components may include fibers, starches, and phytochemicals.

When we eat foods containing prebiotics, they end up in our colons, where microorganisms ferment them for their own food sources.

The byproducts of this fermentation may include healthy fats like butyrate, increased absorption of certain nutrients, and beneficial changes in gut bacteria. (5)

Intake of prebiotics from nutrient-dense foods can also reduce the presence of harmful bacteria that may increase inflammation or symptoms of chronic health conditions.

How Do Probiotics Affect the Body?

The human body plays host to trillions of bacteria, with the majority of bacteria being found in the gut.

The gut microbiota typically has a symbiotic (mutually beneficial) relationship with us, helping with gut integrity, nutrient digestion, immunity regulation, and protecting against harmful bacteria. (6)

Over time, the microbiota naturally develops and changes as we age, relocate to different geographical areas, and spend time with certain people. (7, 8, 9)

The balance of bacteria can be disrupted by certain dietary choices, alcohol intake, chemical consumption, inflammation, stress, and the use of medications like antibiotics.

A disruption of the gut microbiota is called dysbiosis. (10)

Dysbiosis can mean that you have small amounts of good bacteria and yeasts, an overgrowth of bad bacteria and yeasts, or perhaps a low diversity of microorganisms in the gut.

No matter the cause of dysbiosis, this condition can result in increased inflammation, impairments to the gut barrier, and an increased risk of disease.

Introducing probiotics can assist with bringing balance to the gut bacteria by supporting the survival of good bacteria, improving gut integrity, and balancing immune responses in the gut.

Health Benefits of Probiotics

Many of the health benefits of probiotics come from their ability to reduce inflammation, regulate the immune system, and compete with pathogenic bacteria to support the health of the body’s systems.

Digestive Health

Probiotics are most known for their use in the treatment of gastrointestinal illnesses.

Multiple studies find that probiotics can improve microbiota balance in the gut and modify gut bacteria activity.

In an overview of Cochrane systematic reviews on the effects of probiotics on gastrointestinal illnesses published in 2019, researchers determined that there was strong evidence supporting the use of probiotics for treating diarrhea. (11)

The researchers noted that there was not sufficient evidence available to determine the benefits of probiotics for other conditions such as colitis, Crohn’s disease, and liver conditions.

Conversely, a 2018 review suggests that there is high-quality evidence supporting the use of probiotics for infectious diarrhea, ulcerative colitis, IBS, antibiotic-associated diarrhea, functional gastrointestinal disorders, necrotizing enterocolitis, C. diff-associate diarrhea, and hepatic encephalopathy. (12)

The use of probiotics for acute pancreatitis and Crohns was not supported.

May Help Improve Mood and Mental Function

Probiotic supplementation may help with improving mood and brain function.

The gut-brain axis is a phenomenon in which the gut communicates with the brain through nervous system activity and metabolites from gut bacteria.

A 2016 meta-analysis of studies found that supplementation with probiotics had a significant impact on decreasing depressive symptoms in people with major depressive disorder aged under 60 years old. (13)

Supplementation varied in strains of bacteria used and length of probiotic use (between 4–20 weeks), so more research needs to be done to make standard protocols.

Pro-inflammatory conditions such as Alzheimer’s, Multiple Sclerosis, Amyotrophic Lateral Sclerosis, and Huntington’s Disease may negatively impact gut integrity, gut bacteria diversity, and inflammation levels in the intestines.

There are currently inadequate clinical trials on whether probiotics can reduce symptoms of these neurodegenerative diseases, but animal studies appear promising. (14)

May Help Promote Heart Health

Probiotics may support heart health by improving cardiovascular disease risk factors.

A 2020 meta-analysis on the effectiveness of probiotics for patients with cardiovascular disease risk found that probiotic supplementation was able to reduce systolic and diastolic blood pressure, decrease total cholesterol and LDL-cholesterol, improve HDL cholesterol, and reduce BMI, serum glucose, and HgA1c within 1.5 months of use. (15)

High dose of probiotics, use of kefir or a probiotic powder, and interventions lasting greater than 1.5 months were associated with better results.

May Improve Symptoms Related to Diabetes

Probiotic supplements may be beneficial for improving insulin sensitivity, gut barrier strength, and reducing inflammatory immune response in people with diabetes.

Dysbiosis is common in type-2 diabetes due to changes in the gut, including decreased short-chain fatty acid production, increased inflammation and oxidative stress, increased intestinal permeability, and decreased vitamin synthesis.

Studies find that probiotic supplementation may improve the integrity of the gut barrier, decrease cellular stress, and decrease endotoxins that trigger inflammation. (16)

A 2017 review and meta-analysis of the effects of probiotics on metabolism markers during pregnancy found that taking a probiotic for 6–8 weeks was effective in reducing insulin resistance in women with gestational diabetes. (17)

May Contribute to Healthier Skin

Oral or topically applied probiotics may be beneficial for skin health by reducing chronic inflammation, supporting immune cell function, and preventing the growth of harmful bacteria.

A 2019 review on probiotics in dermatology supports the use of oral probiotics for decreasing skin cancer risk, causing remission of dermatosis-arthritis syndrome and rosacea, treating atopic dermatitis, acne, psoriasis, seborrheic dermatitis, and even wound healing. (18)

Certain topical administrations of probiotics may also be beneficial for skin health.

May Help with Weight Loss

Probiotics may support weight loss if taken continuously through the improvement of anthropometric measures, short-chain fatty acid production, reducing inflammation markers, and improvements in metabolism.

In a 2020 review on the use of probiotics for supporting weight loss in overweight and obese individuals, researchers noted that supplementation with probiotic foods or supplements may help with improvements in body composition, body weight, metabolic markers, inflammation, and insulin sensitivity. (19)

Not all studies showed consistent results from probiotic supplementation, and it could be related to the length of supplementation, dosing, or types of probiotic strains used.

More research needs to be done on the optimal combination of probiotics, length of supplementation, and if the weight loss from using probiotics is a significant quantity for individuals.

To be most effective, interventions with probiotics may also need additional factors, such as prebiotic use, dietary changes, and physical activity.

May Be Beneficial for Vaginal Health

Probiotic use may help support vaginal health and reduce the risk of bacterial vaginosis by supporting the growth of good bacteria.

Bacterial vaginosis occurs when the natural balance of lactobacilli bacteria on the vagina are replaced by anaerobic bacteria, causing a change in vaginal pH and other signs and symptoms. (20)

In a 2014 review, researchers found that most of the studies on probiotics and bacterial vaginosis find that the use of probiotics may help prevent or treat bacterial vaginosis. (21)

Probiotics may help maintain a healthy vaginal pH and produce metabolites that prevent the growth of pathogenic bacteria.

May Support Oral Health

The benefits of probiotics may start in the mouth by reducing oral pathogens.

In a 2017 review of studies, supplementation with probiotics including L. Rhamnosus was found to slow the development of gingivitis, potentially be effective for treating periodontal disease, and may decrease colonization of pathogenic bacteria in the mouth. (22)

Sources of Probiotics

Now that you know a bit more about probiotics, you may be wondering how you can get some into your diet.


Fermented foods are a primary source of probiotics, as they have been transformed by the metabolism of bacteria and yeasts.

Foods like kimchi, kefir, yogurt, sauerkraut, tempeh, miso, kombucha and other fermented beverages, salted gherkin pickles, natto, buttermilk, and even certain cheeses (cheddar, mozzarella, and gouda) are sources of probiotics. (23, 24, 25)

In today’s market, some food brands are adding probiotics to foods and beverages that traditionally do not contain these microorganisms.

Examples of these include probiotic juices, coffees, chocolate, granola, and chips.

If you’re choosing one of these processed foods with added probiotics, consider choices that are nutrient-dense and may contain prebiotics to support the further growth of healthy gut bacteria.


Supplements are great for dialing into specific strains of bacteria to help with certain health conditions.

You can purchase probiotic supplements as a capsule, tablet, gummy, protein powder, or they can be found as an ingredient present in other supplements.

Some probiotic supplements are known as symbiotics, meaning that they contain both prebiotics and probiotics together to benefit the gut.

We will go into detail about how to choose a probiotic supplement that is best for you.

How to Choose a Probiotic

We give a full breakdown of how to choose the best probiotic supplement in this article, but I will summarize some steps you should take to choose the best probiotic for you.

1. See If a Probiotic Is Right for You

Not all conditions may benefit from the use of a probiotic supplement, so it is beneficial to see what trusted organizations say about using a probiotic for your situation.

Your physician or dietitian can give additional insight into whether a probiotic is right for you, so speak with a professional before you start.

2. Pick the Right Kind of Probiotic

The benefits of probiotics cannot be generalized to all bacteria or yeast strains, so it is important that you choose the right one.

Check the entire name of your probiotic strains on the Supplement Facts label before you buy it, all the way down to the strain.

Some probiotics work best together, so choosing a supplement with multiple strains may be best for certain conditions.

3. Check the Dosage

Probiotic supplements are measured in colony-forming units, also known as CFUs.

The concentration of microbial CFUs may influence how effective a bacteria strain is for promoting its health benefits.

As a general rule, probiotic supplements should have at least 1 billion CFUs of each microbe strain.

4. Opt for Quality-Tested Probiotics

Not all probiotics are quality tested and match the content that their labels claim.

In one 2015 study, only 1 in 16 tested probiotic products contained the exact bifidobacterial subspecies that were listed on its label. (26)

Check for supplements that have been third-party tested by entities like Consumer Labs, NSF International, or the United States Pharmacopeia (USP).

5. Choose Probiotics That Have Been Stored Properly

Probiotics are very sensitive to breaking down before they reach your gut, so you want to choose products that have not been exposed to excessive heat or moisture.

Buy your probiotics from reputable sources with quality and environmental control.

When you take your probiotic home, store it according to directions – some may require storage in dark spaces or refrigeration.

6. Consider Synbiotics

Get a two-for-one combo with your probiotic supplement by adding prebiotics that can help with keeping your healthy bacteria strong.

How to Take a Probiotic

Once you’ve figured out which probiotic to choose, you should take them in a way to maximize their effectiveness for your health.

Probiotics are extremely sensitive to digestion in the stomach, and not all microorganisms in probiotics will survive past early digestion. (27)

As mentioned before, a reduced number of bacteria surviving in your probiotic may result in an inadequate health response.

Certain companies recommend taking probiotics on an empty stomach in the morning or before bed to maximize effectiveness.

Studies suggest that certain probiotics are likely to survive if taken at least 30 minutes before a meal. (28)

Others recommend that their probiotics be taken with food to get the best results.

Probiotic supplements taken with a small amount of fat or sugar could be beneficial for ensuring that probiotics survive digestion. (28, 29)

I strongly recommend checking the instructions for use on any individual probiotic you plan to take so that you can get the best results.

If you are taking any antibiotics, it is recommended to separate bacteria-derived probiotics from antibiotics by at least two hours to improve bacteria survival. (30)

Overall, the most important thing is to stay consistent with your probiotic use. It may take up to 4 weeks or longer of continuous probiotic use to see benefits in certain conditions. (31)

Probiotics are only able to impact the body while you’re taking them, and the benefits from your probiotic may disappear in as little as 1–3 weeks after you’ve stopped them.

Side Effects and Safety

Probiotics are generally considered safe to use. (32)

The risk from using probiotic foods is low, and probiotic foods have been consumed by people for centuries without much issue.

Several probiotic species are naturally found within the gut microbiota.

Side Effects

There can be some side effects from taking probiotics, especially within the first days of use.

To reduce the occurrence of symptoms, it may be beneficial to start probiotics at half doses or take them on alternate days so that your body can adjust.

Some common symptoms experienced when starting probiotics include gastrointestinal symptoms like nausea, abdominal discomfort, feelings of abdominal tightness, and changes in bowel movements. (30)

These symptoms usually subside after a few days, and you can start taking the full dose of your probiotic supplement.

In some cases, probiotics can trigger an allergic reaction and cause a rash. If you experience a rash or other allergic reactions, please immediately stop taking and seek medical attention. (33)

Who Shouldn’t Take Probiotics?

Probiotics are not suitable for everyone, and there are certain conditions in which probiotics have to be used cautiously.

Individuals with small intestinal bacterial overgrowth (SIBO) may experience increased brain fog, gas, and bloating(34)

In rare cases, probiotic supplementation may cause systemic bacterial infections in people who are severely immunodeficient or have central venous catheters. (30)

There is mixed evidence if probiotics are safe for certain children.

Some studies suggest that probiotics may slightly increase the risk of infection in children in a pediatric ICU setting. (35)

Yet another study suggests that probiotics could be beneficial in preventing severe necrotizing enterocolitis in preterm infants. (36)

Every case is individual, so speak with your doctor before starting a new probiotic.

Frequently Asked Questions About Probiotics

What are probiotics?

Probiotics are bacteria or yeasts that can be beneficial to the human body when taken in certain amounts.

What are probiotics useful for?

Probiotics are beneficial for gastrointestinal health, heart health, weight loss, diabetes management, oral health, mental health, vaginal health, and immune support.

How often should I take a probiotic?

If a probiotic is right for you, it should be taken daily. For certain conditions, you may need to take a probiotic for up to 4–6 weeks to experience benefits.

When should I take a probiotic?

It depends on the supplement.

Certain companies recommend taking probiotics on an empty stomach in the morning, 30 minutes before a meal, or before bed to maximize effectiveness.

Others recommend taking your probiotic with a meal.

Always check the label of your probiotic and follow their directions for best results.

What kind of probiotic should I take?

The probiotic that may be right for you depends on what condition you’re looking to improve.

I recommend speaking with your doctor or dietitian for more information on specific strains, or looking at websites of trustworthy organizations about probiotics and health.

What foods contain probiotics?

Fermented foods such as kimchi, kefir, yogurt, sauerkraut, tempeh, miso, kombucha, and other fermented beverages, salted gherkin pickles, natto, buttermilk, and certain cheeses contain probiotics.

Some companies make beverages and snacks with added probiotics.

What are the side effects from taking a probiotic?

Probiotics are generally safe, but you may experience side effects like nausea, abdominal discomfort, feelings of abdominal tightness, and changes in bowel movements within the first few days.

In rare cases, allergic reactions to probiotics can cause a rash.

Who should not take probiotics?

Probiotics may not be appropriate for some people with compromised immune systems, people who have a central venous catheter, individuals with SIBO, and some children.

The Bottom Line

Probiotics are one tool in supporting gut health and overall health.

Probiotic supplements are a great way to target specific gut bacteria needs if you have a certain condition, though this does require diligently taking a daily supplement.

It may be easier to incorporate probiotic-containing foods and beverages into your lifestyle to get a steady intake of gut-boosting bacteria.

Along with your probiotics, regularly eating foods containing prebiotics (such as dietary fiber) can feed and support the growth of good bacteria in the gut.

What you don’t eat is just as important for supporting your gut health. Moderate your intake of alcohol and pro-inflammatory foods (i.e., highly refined and processed foods).

Even getting enough sleep is important. Sleep deprivation may reduce the diversity of organisms in the gut microbiota, increasing the risk for dysbiosis. (37)

Aim for 7–9 hours of sleep per night.

If you are interested in starting a probiotic for gut health or other health concerns, speak with your doctor first.

They can determine if starting a probiotic is appropriate for you and provide counsel on the best strain to meet your body’s needs.

Was This Article Helpful?YesNo
Thanks for your feedback!
In a few words, please tell us how this article helped you today.
Please let us know how we can improve this article by selecting your concern below.
Thank You! We appreciate your feedback.
* Please select at least one topic:
Please Note: We cannot provide medical advice. This feedback will help us continue improving your user experience on WellnessVerge.
Please Note: We cannot provide medical advice. This feedback will help us continue improving your user experience on WellnessVerge.
Submit Feedback
Submit Feedback

At WellnessVerge, we only use primary references for our articles, including peer reviewed medical journals or well-respected academic institutions.

  1. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic:
  2. Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects:
  3. Bifidobacterium mixture (B longum BB536, B infantis M-63, B breve M-16V) treatment in children with seasonal allergic rhinitis and intermittent asthma:
  4. Yeasts as probiotics: Mechanisms, outcomes, and future potential:
  5. Prebiotics: Definition, Types, Sources, Mechanisms, and Clinical Applications:
  6. Introduction to the human gut microbiota:
  7. Aging progression of human gut microbiota:
  8. US Immigration Westernizes the Human Gut Microbiome:
  9. Close social relationships correlate with human gut microbiota composition:
  10. Current understanding of dysbiosis in disease in human and animal models:
  11. Probiotics and Gastrointestinal Conditions: An Overview of Evidence from the Cochrane Collaboration:
  12. Probiotics for Gastrointestinal Conditions: A Summary of the Evidence:
  13. Effect of Probiotics on Depression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials:
  14. Gut–Brain Axis: Role of Gut Microbiota on Neurological Disorders and How Probiotics/Prebiotics Beneficially Modulate Microbial and Immune Pathways to Improve Brain Functions:
  15. Efficacy of Probiotics in Patients of Cardiovascular Disease Risk: a Systematic Review and Meta-analysis:
  16. Relationship between gut microbiota, probiotics, and type 2 diabetes mellitus:
  17. Effect of Probiotics on Metabolic Outcomes in Pregnant Women with Gestational Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials:
  18. Changing our microbiome: probiotics in dermatology:
  19. Probiotics for the Treatment of Overweight and Obesity in Humans—A Review of Clinical Trials:
  20. signs and symptoms:
  21. Effects of probiotics on the recurrence of bacterial vaginosis: a review:
  22. Probiotics and oral health: A systematic review:
  23. Probiotic bacteria survive in Cheddar cheese and modify populations of other lactic acid bacteria:
  24. Survival of microencapsulated probiotic Lactobacillus paracasei LBC-1e during manufacture of Mozzarella cheese and simulated gastric digestion:
  25. Characterization of the Microbial Diversity and Chemical Composition of Gouda Cheese Made by Potential Probiotic Strains as an Adjunct Starter Culture:
  26. Validating bifidobacterial species and subspecies identity in commercial probiotic products:
  27. National Institutes of Health, Office of Dietary Supplements: Probiotics:
  28. The impact of meals on a probiotic during transit through a model of the human upper gastrointestinal tract:
  29. Survival of Probiotic Lactobacilli in Acidic Environments Is Enhanced in the Presence of Metabolizable Sugars:
  30. National Library of Medicine: Probiotics:
  31. A randomized, double-blind, placebo-controlled multicenter trial of saccharomyces boulardii in irritable bowel syndrome: effect on quality of life:
  32. World Gastroenterology Organisation Global Guidelines: Probiotics and prebiotics:
  33. Long-term treatment with probiotics in primary care patients with irritable bowel syndrome--a randomised, double-blind, placebo controlled trial:
  34. Brain fogginess, gas and bloating: a link between SIBO, probiotics and metabolic acidosis:
  35. Probiotic administration and the incidence of nosocomial infection in pediatric intensive care: a randomized placebo-controlled trial:
  36. Probiotics for prevention of necrotizing enterocolitis in preterm infants:
  37. Gut microbiome diversity is associated with sleep physiology in humans: