The Potential of Probiotics

a set of fermented food: cucumber pickles, coconut milk yogurt, kimchi, sauerkraut, red beets, apple cider vinegar
Photo: Thinkstock/MAREKULIASZ

As scientists discover more about probiotics, it appears these microscopic bacteria may be instrumental to the treatment and prevention of certain infectious diseases, metabolic conditions, immune disorders and neurological disorders.

Probiotics are live, active microorganisms ingested to alter the gastrointestinal flora for health benefits. They often are referred to as “good” bacteria in the gut and compete with “bad” bacteria for adhesion sites to either rid the body of pathogens or increase the host’s immune system. Their benefits were first noticed centuries ago, when people started eating fermented foods. Today, those foods include fermented vegetables, sauerkraut, miso, fermented cheese, kefir, yogurt, tempeh, pickles, kimchi, green olives, wine, natto and sourdough bread. In addition to fermented foods, probiotic supplements are available in pill, powder and chew forms, and some manufacturers have begun adding probiotics to non-fermented grocery items such as water, chips and juice.

The potential benefits of probiotics are widespread, but there is no one-size-fits-all application. Under the umbrella of probiotic genera are hundreds of species with even more strains, each performing a separate function or producing a different benefit in the body when used alone or in conjunction with others. The most widely researched bacterial genera include Lactobacillus, Bifidobacterium and Streptococcus, while yeast varieties include Saccharomyces boulardii.


Lactobacillus bacteria are found in the GI and urinary tracts and are the most abundant bacteria in the vagina. These aerobic, lactic-acid-forming bacteria are the most widely used probiotic in foods such as yogurt. Their ability to form biofilms allows them to survive in harsh conditions, such as the low pH of stomach acid, and maintain colonies in their host.

Lactobacillus acidophilus

L. acidophilus is the most common species of Lactobacillus. Research suggests it may help certain vaginal conditions, treat diarrhea and boost immunity.

Suppositories of L. acidophilus have been successful in treating bacterial vaginosis, and some research shows the ingestion or application of yogurt to the vagina can help prevent yeast infections. In combination with other forms of Lactobacillus, research suggests it may prevent traveler’s diarrhea; antibiotic-associated diarrhea, or AAD; and Clostridium difficile when taken with antibiotics. In some instances, L. acidophilus reduced the incidence of eczema in infants when it was taken orally by their pregnant or breast-feeding mothers.

Dietary sources of L. acidophilus include certain brands of yogurt and milk, miso and tempeh. It also is available as pills, freeze-dried granules, powders and vaginal suppositories. Probiotic supplements should be refrigerated to maintain quality. Recommended doses vary but range from 1 billion to 15 billion colony forming units, or CFU, per day.

Lactobacillus helveticus with Bifidobacterium longum

Together, L. helveticus and B. longum may have immune-boosting properties and the ability to treat psychological conditions, improve overall health and skin conditions, such as atopic dermatitis. Individuals given a daily probiotic blend reported lowered feelings of anxiety and depression. When used alone, L. helveticus was associated with improved quality of sleep and increased serum calcium levels in elderly individuals.

L. helveticus is most commonly used in the fermentation of milk for producing Italian and Swiss cheeses. In addition, both species can be found in kefir, certain yogurts and in supplement form. Currently, there is no recommended dosage, but an intake of 3 billion CFU per day showed improvements in anxiety and depression in studies.

Lactobacillus delbrueckii subsp. bulgaricus with Streptococcus thermophilus

The probiotic combination of L. delbrueckii subsp. bulgaricus and S. thermophilus is most commonly found in yogurt and may be used to increase immunity. One pilot study found that patients in the ICU for traumatic brain injury showed a significant reduction in length of stay and a reduced risk of infection after taking a daily blend of 100 billion CFU of B. longum, L. bulgaricus and S. thermophilus. Another study saw a significant improvement in a marker of non-alcoholic fatty liver disease after taking 500 million CFU of L. bulgaricus and S. thermophilus daily.

All yogurt containing live and active cultures will have L. delbrueckii subsp. bulgaricus (or L. bulgaricus) and S. thermophilus; the two work synergistically to create yogurt by feeding off the other’s byproducts. In addition, the combination can be found in supplements.

Lactobacillus plantarum

L. plantarum may have a significant impact on its host by improving psychological health, increasing immunity and improving metabolic conditions. Several studies have shown a daily intake of L. plantarum can reduce anxiety and depression and may improve symptoms of autism.

Intake of L. plantarum might be beneficial in certain metabolic disorders by reducing BMI, improving blood pressure, decreasing cholesterol and reducing fat oxidation. It also may decrease the development of cardiovascular disease in smokers. Other studies have found supplementation may decrease allergy symptoms in children.

L. plantarum can be found in fermented vegetables such as kimchi, fermented beets, pickled cucumbers, pickled beans and sauerkraut. Other sources include fermented juice drinks and green olives. Although no exact dose is recommended, many over-the-counter supplements contain anywhere from 3 billion to 10 billion CFU.

Lactobacillus reuteri

L. reuteri may reduce inflammation and allergies and serve as a potential treatment for pro-inflammatory diseases. Several studies have shown a reduction of infection and inflammatory markers in diseases such as rheumatoid arthritis, cystic fibrosis and general allergies and inflammation of the airways. In addition, research suggests this probiotic may lessen eczema in children, and oral supplementation may decrease dental carries.

L. reuteri can be found in certain fermented vegetables and dairy products, and also is available in supplement form. Doses used in studies ranged from 100 million to 10 billion CFU per day.

Lactobacillus rhamnosus GG

L. rhamnosus GG, or LGG, is more likely to survive in the gut compared to other species of the Lactobacillus genus. It is one of the most effective probiotics for treating infectious diarrhea and may be used to promote vaginal health (with L. reuteri) and treat certain pediatric conditions.

In addition to treating acute diarrhea in children, LGG also may prevent dental caries and improve infant neurological health, reducing the risk of developing ADD or ADHD. Supplementation of LGG and L. reuteri together may decrease the risk of bacterial vaginosis and promote growth of beneficial bacteria. In studies using a vaginal suppository, the risk of yeast infection declined.

LGG can be found in kefir and certain brands of kombucha drinks and yogurt, as well as supplements and powders. The American Academy of Pediatrics states that LGG is the most effective probiotic for acute infectious diarrhea in children and is dose-dependent past 10 billion CFU. However, the American Academy of Pediatrics does not recommend the use of probiotics in children with compromised immune systems.

Lactobacillus casei

Studies on L. casei suggest it may play an important role in the gut-brain axis by improving mental and neurological health. Supplementation of L. casei resulted in significant decreases in anxiety and depression in individuals with chronic fatigue syndrome and improved mood and cognition in people with autism. Supplementation also has been associated with improved symptoms of multiple sclerosis and improved cognition.

L. casei is available as pill supplements and some chewable forms for children. It also is used in certain dairy and non-dairy yogurts, kefir and kvass, a fermented beverage. Study doses ranged from 100 million to 8 billion CFU per day.


Bifidobacterium inhabits the gut, mouth and vagina. As one of the first bacteria to inhabit the gut, this microorganism aids in the digestion of foods, producing short-chain fatty acids and reducing inflammation through the stimulation of immune cells.

Bifidobacterium bifidum

Research suggests B. bifidum may boost immunity and improve eczema in infants. It also is a hopeful treatment for certain GI conditions, such as constipation, traveler’s diarrhea, IBS, ulcerative colitis and H. pylori.

Food sources of B. bifidum include yogurt, kefir, buttermilk, miso, tempeh, pickles, kimchi, cured meats, some wines and vinegars, sauerkraut and sourdough bread. Supplements also are available. Although there is no recommended dosage, many studies saw benefits at around 1 billion CFU per day.

Bifidobacterium infantis

B. infantis may be beneficial to mental health and possess anti-inflammatory properties. Early research showed that a blend of probiotic strains that included B. infantis improved symptoms of anxiety, depression and autism spectrum disorder. Although B. infantis may be found in certain dairy products, such as yogurt, it is more common as a supplement.

Saccharomyces boulardii

In contrast to bacterial probiotics, S. boulardii is a yeast that has been used for nearly 30 years to treat several gastrointestinal conditions. This probiotic has been used in the treatment and prevention of diarrhea in children and infants. It often is used to prevent diarrhea in patients with feeding tubes and may be effective in adults for AAD, traveler’s diarrhea and diarrhea from C. diff.

This yeast is used to make kombucha and also is available as a supplement. Doses ranging from 250 to 1,000 milligrams of S. boulardii daily for two to four weeks have been used in adults with diarrhea and 250 to 750 milligrams daily for children with diarrhea, not exceeding more than five days.

Putting it Into Practice

While certain strains and species may work together to provide health benefits, there is not enough scientific evidence to justify recommending probiotics in large combinations at high doses. Robin Foroutan, MS, RDN, HHC, spokesperson for the Academy of Nutrition and Dietetics, says she has more success starting patients on low doses, such as 3 billion to 5 billion CFU rather than 100 billion CFU. She explains that too much at one time can result in symptoms such as gas, bloating, constipation or diarrhea.

When deciding on probiotic supplements versus food, dietitians have differing preferences. Emily Parker, MS, RDN, at California State University–Long Beach, and co-author of several comprehensive probiotic summaries, prefers recommending food before supplements. “I suspect that there are benefits to fermented foods that may go beyond the strains of bacteria — the bioavailability of some vitamins and minerals is elevated by the fermentation process of vegetables,” Parker says.

Conversely, Heather Finley, MS, RD, LD, CEDRD, CLT, doctoral student and one of several co-authors with Parker, prefers recommending supplements in addition to food at the start. “The fastest way to change the microbiome is through diet, but a probiotic supplement can be a great option for clients because they provide bacterial diversity and most provide high amounts of CFU,” Finley says. “In some cases, fermented foods can exacerbate GI conditions and a probiotic supplement may be better tolerated.”

When it comes to supplements, Parker trusts products labeled “Good Manufacturing Practices” (GMP) by NSF International, a third-party organization that tests and audits nutritional supplements for quality standards.

Whether from food, drink or pill, the potential benefits of probiotics are promising. As the National Institutes of Health continues its extensive research through the Human Microbiome Project, more findings are guaranteed, and registered dietitian nutritionists have a large part to play in reviewing research and finding what works best for patients.

Esther Ellis
Esther L Ellis, MS, RDN, LDN, is an associate editor of Food & Nutrition Magazine.