Probiotic Supplements: How to Choose What Actually Works

What are probiotics and how do they work?

Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. They are often called “good” or “helpful” bacteria because they can support the balance of microbes in the gut and other parts of the body.

How they work is not completely understood, but research suggests they can affect the composition of the gut microbiome, support the intestinal barrier, modulate the immune system, and produce beneficial compounds. However, the effects are strain-specific: different strains of probiotics have different benefits, and evidence for one strain does not necessarily apply to another.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, Harvard T.H. Chan School of Public Health, National Center for Complementary and Integrative Health (NCCIH), NIH

Common probiotic strains and their uses

Probiotics are identified by their genus, species, and strain. The most common genera include Bifidobacterium, Lactobacillus (members of the family Lactobacillaceae), Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus.

Different strains have been studied for various conditions, including antibiotic-associated diarrhea, infant colic, periodontal disease, and ulcerative colitis, but in many cases it is unclear which strains are helpful and how much to take. For example, Lactobacillus rhamnosus GG has been shown to reduce the risk of antibiotic-associated diarrhea in children and adults, while Bifidobacterium longum 35624 is often used for digestive support.

• Bifidobacterium longum 35624: studied for digestive support.
• Lactobacillus rhamnosus GG: has evidence for reducing the risk of antibiotic-associated diarrhea.
• Saccharomyces boulardii is a yeast-based probiotic that has been studied for antibiotic-associated diarrhea.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, National Center for Complementary and Integrative Health (NCCIH), NIH, WebMD

Understanding CFUs and viable counts

CFU stands for colony-forming units, a measure of the number of viable (live) microorganisms in a product. The CFU count on a label indicates the number of live cells present at the time of manufacture, but not necessarily at the time of consumption.

Current U.S. regulations only require listing the total weight of microorganisms, not the CFU, so manufacturers may voluntarily list CFU. Some responsible manufacturers list the CFU expected at the end of the product's shelf life, which is a better indicator of what you will consume.

Higher CFU products are not necessarily more effective than lower CFU ones. Effectiveness depends on the strain and the condition being targeted.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, Harvard T.H. Chan School of Public Health

Forms of probiotics: capsules, powders, and foods

Probiotic supplements are available in various forms, including capsules, powders, liquids, and other formats. Fermented foods such as yogurt and kefir can also contain probiotics, but not all fermented foods contain live cultures after processing. Labels may indicate “live and active cultures,” which can help you identify foods that contain them.

Choosing a form is often a matter of personal preference and convenience, but the effectiveness depends on the specific strain and dose rather than the form itself.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, Harvard T.H. Chan School of Public Health, Cleveland Clinic

Reading probiotic labels

A good probiotic label should list the genus, species, and strain of each microorganism, as well as the CFU count at the end of shelf life. This full identification is important because research links benefits to specific strains.

Also check for allergens such as dairy, egg, or soy, and look for any mention of “live and active cultures” if you are considering a food product.

Be aware that some commercial probiotic supplements have been found to contain microorganisms other than those listed on the label, which can pose health risks. This highlights the importance of choosing products from manufacturers that assure potency, purity, and identity.

• Look for the full strain name (genus, species, strain).
• Check the CFU count listed as expected at the end of shelf life, not just at manufacture.
• Consider third-party testing or certifications when available, but know that the FDA does not pre-approve dietary supplements.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, National Center for Complementary and Integrative Health (NCCIH), NIH, Harvard T.H. Chan School of Public Health

How to choose a probiotic for your needs

Start by identifying your specific health goal, such as reducing antibiotic-associated diarrhea or improving digestive comfort. Then look for strains that have been studied for that condition, keeping in mind that evidence is strain-specific.

For example, Lactobacillus rhamnosus GG has evidence for reducing the risk of antibiotic-associated diarrhea, while Bifidobacterium longum 35624 is often used for general digestive support. Always check the label for the full strain name and a guaranteed CFU count through the expiration date.

Consult a healthcare professional for personalized advice, especially if you have underlying health conditions or are taking medications.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, National Center for Complementary and Integrative Health (NCCIH), NIH, Harvard T.H. Chan School of Public Health

side effects

Probiotics are likely safe for most healthy adults, but side effects can occur. The most common are gas and bloating, and some people may also experience diarrhea. These symptoms usually clear up within a few days or weeks as your body adjusts.

The risk of harmful effects is greater in people with severe illnesses or compromised immune systems. Severe and even fatal infections have been reported in premature infants given probiotics, leading the FDA to warn healthcare providers about this risk. Other potential harms include the production of harmful substances by the probiotic organisms and the transfer of antibiotic resistance genes to other microbes in the digestive tract.

• High-risk groups: premature infants, seriously ill patients, and immunocompromised individuals should avoid probiotics unless under medical supervision.

Sources: National Center for Complementary and Integrative Health (NCCIH), NIH, Medical News Today, Cleveland Clinic

Storing probiotics

Probiotics are living organisms, so their viability depends on storage conditions. Many products need refrigeration to maintain potency, but some are shelf-stable. Always read the label for specific storage instructions.

In addition, check the expiration date and aim to purchase products that guarantee CFU through that date, ensuring you consume live organisms.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, Harvard T.H. Chan School of Public Health

Evaluating probiotic product quality

When choosing a probiotic supplement, focus on the label's strain identification, the CFU count at the end of shelf life, and the manufacturer's quality assurances. Look for products that specify the exact strain and a CFU count that is guaranteed through the expiration date, as this indicates the manufacturer has taken steps to ensure potency.

The table below summarizes the key criteria to compare across products without focusing on a specific brand.

Sources: National Institutes of Health (NIH) Office of Dietary Supplements, Harvard T.H. Chan School of Public Health