Probiotics: Potential Benefits, Known Risks, and More

Note: The U.S. Food and Drug Administration (FDA) does not approve supplements for safety or effectiveness. Talk to a healthcare professional about whether a supplement is the right fit for your individual health, and about any potential drug interactions or safety concerns.

Your body is home to trillions of microorganisms that help you function at your best every day.

Some of these microbes are probiotics — a group of good-for-you bacteria and yeast that play a role in helping you digest food, fend off diseases, and even create vitamins.

Probiotics exist naturally in the body and in certain fermented foods.

The idea of supplementing with probiotics may seem like a relatively new area of nutrition, but it dates back to the early 1900s, when a researcher named Elie Metchnikoff first experimented with certain bacteria strains.

There is still a lot scientists don’t understand about probiotics, but research has identified several of their functions and benefits.

Eating probiotic-rich foods and taking probiotic supplements can help populate your gut with beneficial bacteria, says Sarah Pflugradt, PhD, RDN, a registered dietitian and adjunct professor of health communication at American University in Washington, DC. “The goal is to have a microbiome that is not just full of good bacteria, but full of different types of good bacteria — often referred to as gut diversity,” she says.

Why? Because lots of gut diversity has been linked to a variety of health benefits, including better digestion and metabolism, improved mood, and a lower risk of many different diseases.

To reap these benefits, you may be interested in a quick fix such as a probiotic supplement, but it’s important to understand that what we know about them is limited.

“We know that probiotic bacteria are beneficial for health, but research on why and how they impact health is still emerging,” Dr. Pflugradt says. “I wouldn’t necessarily say their role in specific conditions is theoretical, but it needs to be studied more.”

And that’s especially true when it comes to supplements. Even though the research on their benefits is promising, probiotic supplements are not widely recommended yet, Pflugradt says. You’re much better off getting probiotics from food, which offer a wider variety of probiotic bacteria, she says. Supplements, on the other hand, typically only contain one or two specific strains, which don’t have as much of an effect on gut diversity.

Here’s a look at the evidence we have to date.

May Improve Digestive Health

Probiotics, whether by way of food or supplements, may help reduce diarrhea caused by antibiotic use, cancer therapy, or hospital infections.

Some strains of probiotics (different types of good bacteria) may be more helpful than others. Streptococcus and lactobacillus bacteria strains can help, but doctors also use yeast strains, such as Saccharomyces boulardii, to prevent diarrhea.

Probiotics from milk products may also help people with lactose intolerance better digest dairy. Lactose intolerance is caused by a deficiency in the enzyme lactase that helps break down the natural sugars in dairy foods.

A meta-analysis of 12 studies found that several strains of probiotics, including streptococcus and lactobacillus, were associated with a reduction of lactose intolerance symptoms, including abdominal pain, diarrhea, and flatulence.

It’s worth noting that some of the studies looked at the effects of probiotic supplements alone, while others studied the effects of probiotic-fortified dairy foods such as ice cream or yogurt.

Probiotics may also help with inflammatory bowel disease (IBD), a group of autoimmune diseases marked by chronic inflammation in the gut that leads to symptoms such as abdominal pain, nausea, fatigue, chronic diarrhea, and weight loss.

Crohn’s disease (CD), ulcerative colitis (UC), and indeterminate colitis (IC) are three types of IBD. Clinical trials suggest that probiotic supplements may be a promising therapy for UC.

Unfortunately, the same therapeutic effect was not found with CD or IC.

Some research suggests that probiotics (from food or supplements) can help relieve symptoms of irritable bowel syndrome (IBS), a diagnosis used for unexplained digestive symptoms that last for at least three months, such as gas, bloating, abdominal pain, diarrhea, and constipation.

One review, for example, concluded that probiotics can help reduce overall symptoms of IBS and improve quality of life in people with the condition.

Other research has found that taking probiotic supplements may help ease symptoms of depression in people with conditions such as IBS, although the reasons aren’t totally clear.

If you have one of these conditions and are curious about probiotics, speak with your care team. “It’s always a good idea to consult with your primary care physician or a registered dietitian if you want to take a probiotic, to ensure it’s right with your current medical conditions and medication, especially if you are immunocompromised,” Pflugradt says.

Also, one study found that taking probiotic supplements (namely lactobacillus) while pregnant may help reduce nausea, vomiting, and constipation.

However, pregnant women should speak with their healthcare provider to make sure probiotics are the best option for them.

May Help Reduce Inflammation

Probiotic supplements seem to have an anti-inflammatory effect in the body, although more research is needed on the effects of specific strains and dosages.

“Probiotic bacteria in the gut produce substances called short-chain fatty acids, and research has pinpointed these as the real heroes of the gut,” Plfugradt says. They help reduce inflammation in the body, and this may benefit many conditions that stem from chronic inflammation, from type 2 diabetes to arthritis.

Indeed, a systematic review and meta-analysis that looked at 22 high-quality studies found that probiotic supplements have a positive effect on the management of type 2 diabetes, although the authors noted that more research needs to be done to determine the best probiotic strains and dosages to use, and for how long.

Likewise, another systematic review and meta-analysis found that probiotics can help reduce inflammation, regulate immunity, and improve pain scores in people with inflammatory arthritis. But again, more research is needed before we know which strains and doses are most effective for this condition.

May Offer Immune System Support

You may think of your immune system and your gut as two separate entities, but they’re actually intricately related.

“Probiotics are meant to improve the health of the microbiome,” Pflugradt says. “When these good bacteria populate the gut, they don’t allow harmful bacteria to grow, improving the immune response.”

One research review found that consuming probiotics may improve immune function in two important ways: by stimulating the production of cytokines, the proteins that control the growth and activity of other parts of the immune system, as well as by stimulating cells that produce immunoglobulin-A, an antibody that helps your body fight off pathogens.

At the same time, there is a lot we still need to understand about how different strains of probiotics affect the immune system in different people.

May Help Reduce Cancer Risk

Because more and more research has linked the gut microbiome to the immune system, scientists are studying how probiotics’ specific effect on immunity may potentially help in the prevention and treatment of cancer.

So far, much of the research in this area has involved lab and animal studies on probiotic strains commonly found in dairy products and certain supplements. These probiotics seem to decrease the enzyme activity of other bacteria that produce cancer cells, meaning they may potentially reduce the risk of liver, colon, and bladder cancer.

However, these studies are in the very early stages, and we are a long way from being able to say probiotics can reduce cancer risk in humans.

Given these limitations, a research review noted that probiotics have theoretically been shown to be effective against various cancer types and may also be helpful as an adjunctive therapy for people undergoing chemotherapy for cancer, although more large-scale randomized controlled trials are needed to determine the overall safety and efficacy of various probiotic formulations and treatment durations.

Additionally, one observational study that spanned 20 years and included nearly 37,000 people found that low and moderate intake of probiotics from food was linked to a reduced risk of death from cancer.

It is important to keep in mind here, though, that observational studies like this one can only draw connections (in this case, between eating probiotic-rich foods and a lower risk of cancer), but they don’t control for other factors (such as other lifestyle habits) that may play a role, so they can’t prove cause and effect.

The bottom line here is that the potential anticancer perks require a lot more study, including large-scale clinical trials in humans to help us better understand the role of probiotic strains and the dosages that might yield these effects.

“There are currently not any recommendations for using probiotic supplements for cancer prevention,” Pflugradt says. In the meantime, it is known that consuming probiotic-rich foods is part of a healthy diet, she adds. “From an overall health perspective, regularly eating probiotic-rich foods can help with immunity and fighting inflammation.”

May Help With the Prevention of Allergies

Probiotics seem to influence an entire immunological network in the body, and these effects may start even before you’re born. Some research suggests that supplementation with certain probiotics during pregnancy may reduce the child’s risk of developing allergic conditions such as eczema, especially if the child is at high risk of developing allergies.

Results have been inconsistent in this area, though, so more large studies need to be done to better understand the mechanisms and the exact role that probiotics play.

May Lower the Risk of Severe Outcomes From COVID-19

A systematic review and meta-analysis looked at studies done on the effects of probiotics on the prevention and treatment of COVID-19 and found that while probiotics don’t seem to prevent the condition, they are linked to a quicker recovery time and a decreased risk of dying when used during treatment.

The review included many different forms of probiotics, though, so we don’t know which strains or regimens are most effective.

May Lead to Better Oral Health

Probiotics may benefit the digestive tract from beginning to end, and the perks may start in your mouth.

A small amount of research has found that probiotic supplements, specifically lactobacilli, can help balance the pH in your mouth, preventing bacteria from forming into the plaque that leads to cavities and gum disease.

In addition to a balanced pH level in the mouth, practicing good oral hygiene, avoiding foods and drinks with added sugar as much as possible, and seeing your dentist regularly can all help you maintain good oral health.

May Reduce the Risk of Food Allergies

Probiotics may also help prevent food allergies, though more research is needed.

A research review noted that probiotics’ ability to help balance the gut microbiome and support the immune system may help alleviate food allergies. However, the authors note that much of the research in this area has been done only in animals and that food allergies in humans are complicated and affected by many factors, including environment, genetics, and diet. With that in mind, more research is needed to better understand how probiotics affect allergies.

Another growing area of research on probiotics is weight loss.

For example, one review suggested that lowering inflammation by improving gut bacteria may combat insulin resistance, the hallmark of type 2 diabetes, as well as reduce fat accumulation.

Also, a systematic review and meta-analysis found that using a probiotic supplement was associated with decreases in body mass index, weight, and fat mass, with a probiotic dose of at least 30 billion for greater than 12 weeks.

The authors stated that the amounts, type, and duration of the probiotics require further study, because these measures weren’t consistent across every study. If you’re interested in consuming probiotics in food or supplement form for weight loss, talk to your doctor or dietitian for guidance.

Though probiotic supplements are generally safe, they can pose health risks for certain people. If you have a disease or condition that has weakened the immune system and you are sick, the risk of infection may be higher when taking probiotics.

Pflugradt reiterates that it’s best to discuss with your doctor whether taking a probiotic supplement is right for you, based on your health status and the medications you’re taking. People who are immunocompromised should be especially cautious. And, Pflugradt adds: “Probiotic supplements are not recommended for premature or newborn infants unless under the care of a physician.”

Other possible side effects include bloating, gas, and diarrhea, although these are usually mild and tend to go away within a few days or weeks as your body adjusts, Pflugradt says.

Probiotic supplements come in several different forms, including:

Capsules and tablets
Gummies
Liquids
Powders

Certain foods naturally contain beneficial bacteria that support a healthy microbiome, partly by a process called lactic acid fermentation. This occurs when microorganisms such as leuconostoc, streptococcus, and lactobacillus bacteria help convert sugar to lactic acid.

“Probiotics from foods are either naturally made through fermentation, such as in sauerkraut, kimchi, yogurt, or tempeh, or live and active bacteria are added in after processing or pasteurization, like in some yogurts or commercial kombucha,” Pflugradt says.

Foods that contain probiotics include:

Yogurt
Kefir
Fermented cheeses, such as buttermilk cheese and cottage cheese
Kimchi
Raw sauerkraut
Tempeh
Miso
Kombucha
Natto
Lacto-fermented vegetables, such as pickles

Beer and sourdough bread are fermented, but these foods do not contain the live beneficial bacteria we call probiotics.

In general, the body benefits most from probiotics it receives via food, which often also contains beneficial nutrients.

“I prefer probiotics from food because you will likely get a wider variety of probiotic bacteria from various foods,” Pflugradt says. “With supplements, you are only guaranteed to get the probiotic in that supplement, which typically contains one or two different strains.”

If you’re interested in trying a probiotic supplement to help with digestive issues or for other potential health benefits, it’s best to first talk to your doctor or a registered dietitian for guidance on the best strain and regimen for your health goals.

Selection

Here are some things to consider when choosing a probiotic supplement.

Be choosy. In particular, work with your healthcare team to identify and buy the best probiotic supplement for you. Most research has been done on the bacterial strains lactobacillus and bifidobacterium and the yeast strain Saccharomyces boulardii, but it’s also likely that certain strains are better for certain conditions.

Put quality first. Understand that the U.S. Food and Drug Administration doesn’t review dietary supplement products for safety and effectiveness before they’re marketed. To choose a quality supplement, check the label for certifications from USP, NSF, or ConsumerLab. This means the product has undergone third-party testing for quality and purity.

Read the label. Make sure any probiotic you choose is free of any ingredients you do not want, such as food allergens. Your healthcare team can help you understand any terms you aren’t familiar with.

Storage

Keep in mind that probiotic supplements are sensitive to heat and moisture, so they should be stored in a cool, dry place. Some may require refrigeration (check the label), while others — like those that are freeze-dried — may not. For optimal effectiveness, don’t take the supplement with extra-hot foods or beverages.

Dosing recommendations vary depending on the specific health issue you’re taking them for. There is no specific dosage recommendation when taking probiotics for general health, so it’s best to consult with a healthcare provider and follow the instructions on the product’s label.

If eaten in food, the risks of probiotic overdose are low. With supplements, it’s a different story. Some strains could potentially overgrow and cause infections, so it’s important that you discuss your specific probiotic supplements with your healthcare team before you take any, if you are being treated for a current infection. Bacterial overgrowth is more of a risk if you have an immune system disorder (such as cancer and autoimmune diseases), are a premature infant, or have cardiac valve disease, short bowel syndrome, or central venous catheters.

Probiotics show promise for a plethora of health benefits, including better digestive health, improved oral health, and reduced cancer risk, but we need more research to confirm these benefits and better understand which strains and doses are most effective.
Probiotics are found in supplement form as well as in a variety of fermented foods, which offer additional nutritional benefits.
Probiotic supplements are generally considered safe for most people, but it’s always best to consult with your healthcare team before trying a supplement, especially if you’re managing a condition or taking medication.
Currently, probiotic supplements are not recommended for general gut health, but they may be prescribed to help treat diarrhea from antibiotics or certain infections.

With additional reporting by Kaitlin Ahern.

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