Young Ju, Ph.D.

During the last few decades, research into the gut bacterial community has increased and has clarified the importance of probiotics on health and disease. To better understand how they can help you, some terminology may be useful.  

Terminology (1, 2)

Probiotics are live microorganisms (mainly bacteria but also yeasts) that can benefit your health when consumed in adequate amounts.

Prebiotics are substances that are selectively utilized as food by probiotics in the gastrointestinal tract and have health benefits (e.g., non-digestible dietary fiber such as insulin and fructo-oligosaccharides found in whole grains, bananas, greens, onions, garlic, soybeans and artichokes, etc.).

Synbiotics (also called symbiotics) are a combination of probiotics and prebiotics.

The activity and composition of microorganisms in the gut are referred to as the gut microbiota.

Gut Microbiota (3)

The human body is host to about 100 trillion microorganisms (also called microbes) including bacteria, viruses, and yeasts. About 80% of these microorganisms live in the gut (intestine), but not all of these microorganisms are friendly to human health. Microorganisms like probiotics can have beneficial effects on many health conditions.

The huge variability of gut microbiota in the general population begins at birth and even changes seasonally. This variability is influenced by many internal and external factors, such as:

• Delivery method: There are more diverse gut microbiota in babies born at full term compared to premature babies, babies delivered by vaginal birth, and babies that are breastfed compared to formula-fed.

• Age: The number and diversity of probiotics decrease with age.

• Gender: Women have more diverse microbiota compared to men.

• Body weight: Microbiota are more diverse in lean people compared to obese people.

• Physical activity: Athletes show more diversity compared to sedentary individuals.

• Host genotype: Genetic regulation in hosts affects gut microbiota.

• Drug or substance use: As an example, antibiotics reduce diversity.

• Food and diet: Food components and food processing significantly affect gut microbiota.

Fermented Foods and Probiotic Supplements (4, 5, 6)

We can also get probiotics from fermented foods, beverages, and probiotic supplements.

Many types of fermented foods are consumed around the world including dairy (e.g., yogurt, kefir, cheese), meat (sausage), fish (fish sauce, fermented fish), vegetables (kimchi, sauerkraut, pickles), fruits (pickles), legumes (miso, natto, soy sauce), cereals (sourdough), and alcoholic beverages (apple cider, wine, beer, vinegar).

Some fermented foods (yogurt, kefir, most cheese, miso, natto, tempeh, kombucha) require live microbes as starters;  others (pickles in brine or vinegar, cured meat and fish, etc.) do not require starters. In most fermented foods, probiotics content and strains are not known and not listed in the Nutrient Facts panel. Some fermented food products show probiotics content in Colony Forming Units (CFUs), an estimate of the number of viable microorganisms. Some products may state live cultures, live probiotics, or active probiotics but not specify their contents.

During fermentation, probiotics in fermented foods also produce their metabolites, called postbiotics, that may also have health benefits. Numerous studies have found that more diverse fermented food intake is associated with higher diversity in the gut microbiota.

Various probiotic supplements are available. These usually contain 1-10 billion CFU per serving in capsules, powder, liquid, or other forms. Some products contain up to 50 billion CFU or more. Note that a higher CFU doesn’t necessarily mean better health effects.

Synbiotic supplements are also available, which may be more effective than probiotics alone because they work together to optimize gut microbiota. However, the exact effects and benefits of synbiotics depend on the composition of the products and the specific health.

Approximately 70-90% of probiotic microorganisms cannot survive in a low-acid environment,  such as in the stomach. The survival rates of probiotics are affected by many factors, including acidity, probiotics species, and strains, and their abilities to colonize within the host microbiota. To improve the survival rate, enteric coating and microencapsulation methods are used as protective layers applied to capsules or tablets.

Health Benefits of Fermented Foods and Probiotic Supplements (2, 7, 8, 9)

Probiotics have been associated with many short-term and long-term health benefits, with gut and immune health being the most studied. Probiotics may serve to:

• Modulate the gut microbiota and relieve gastrointestinal disorder symptoms (including diarrhea, inflammatory bowel disease, and irritable bowel syndrome).

• Reduce the risk of developing atopic dermatitis and enhance   cognitive function in both healthy elderly people and individuals with mild cognitive impairment.

• Lower cholesterol.

• Reduce body weight, body mass index, and waist circumference in obese people.

• Act as an antioxidant.

• Have an anti-carcinogenicity on breast cancer and colorectal cancer.

• Exhibit antimicrobial and antipathogenic effects. Have a reverse association with mental health such as stress-related diseases and anxiety.

• Enhance sleep quality and sleep time.

 The position statement on probiotics by the International Society of Sports Nutrition (10) addressed several health benefits of probiotics in athletic populations: 

• Certain probiotics strains (e.g., Lactobacillus plantarum, Bifidobacterium longum, Lactobacillus rhamnosus) can increase absorption of protein, which could improve the overall effectiveness of protein utilization, recovery, muscle growth, and immune function.

• Excessive training load, psychological stress, disturbed sleep, and extreme environmental conditions could suppress immune function, contributing to increased risk of respiratory tract infections. Specific probiotic strains (Lactobacillus casei Shirota, Lactobacillus rhamnosus GG, Bifidobacterium lactis, Lactobacillus helveticus, Lactobacillus fermentum) can reduce the number of episodes, severity and duration of upper respiratory tract infections.

• Intense prolonged exercise, especially in the heat, has shown to increase gut permeability which potentially can result in systemic toxemia. Specific probiotic strains (Lactobacillus rhamnosus GG, Bifidobacterium longum, Lactobacillus plantarum, Saccharomyces boulardii, Bifidobacterium lactis) can improve the integrity of the gut-barrier function.

• Selected anti-inflammatory probiotic strains (Lactobacillus rhamnosus GG, Bifidobacterium longum, Lactobacillus casei Shirota, Lactobacillus plantarum) are linked to improved recovery from muscle damage.

• The minimal effective dose and method of administration of a specific strain vary from one study to another.

• Available human studies have shown potential benefits relevant to the athletic population including improved body composition and lean body mass, normalized age-related declines in testosterone levels, reduced stress hormone levels, reduced exercise-induced lactic acid, increased neurotransmitter synthesis, cognition and mood.

Choosing the Right Probiotic Strain(s) (11)

There is no gold standard for choosing the right probiotic strain(s). It depends on your health goals, lifestyle, and existing conditions. For example,

• To improve gut health and digestion: Lactobacillus acidophilus, Bifidobacterium lactis, Lactobacillus plantarum

• To enhance immunity and reduce infections: Lactobacillus rhamnosus, Lactobacillus casei, Bifidobacterium lactis

• To improve gut barrier integrity: Lactobacillus plantarum, Lactobacillus rhamnosus, Bifidobacterium longum

• To improve exercise recovery and performance: Lactobacillus plantarum, Bifidobacterium longum

• To support mental health and mood: Lactobacillus helveticus, Bifidobacterium longum

Potential Side Effects (12)

In general, taking fermented foods and probiotic supplements is safe for most people. Temporary side effects include gas, bloating, constipation, headaches, or allergic reactions. Usually, these side effects are self-limiting. If they continue for more than a few weeks, stop taking the probiotic and consult a medical professional.

Ingesting probiotics may cause harmful effects including infections and blood toxicities for people with a weakened immune system, including people taking immunosuppressant drugs, people with critical illnesses, people with internal bleeding, and newborn/preterm infants. People with dietary restrictions (e.g., vegans) or allergies should also check for ingredients.

Regulation (12, 13)

In the U.S., probiotics are classified as either foods or supplements and may make specific claims in their advertising and/or labels. Probiotic supplements do not undergo the testing and approval process that prescription drugs do.

The U.S. Food and Drug Administration requires certain information be disclosed in the Supplement Facts label, including:

• the genus, species, and strain of each probiotic

• the number of live probiotic microorganisms in each serving (by CFU)

•  any extra ingredients

•  expiration date

•  suggested serving size

• health benefits

• proper storage conditions

Currently, there is no objective system for rating health claims made by probiotic products. Manufacturers are responsible for the safety and efficacy of supplements. 

The World Gastroenterology Organization advises restricting probiotics use to the strains and indications that have proven efficacy (14). 

The International Scientific Association for Probiotics and Prebiotics advises manufacturers to list the total number of CFUs–ideally for each strain–on the label. They also suggest consumers avoid products that list the CFU counts at time of manufacture (15).

Conclusion

Tennis players interested in enhancing their health and fitness should consider themselves “pro” probiotics. Research has shown that fermented foods and probiotic supplements can improve many conditions including gastrointestinal disorders and inflammation. Health professionals and researchers may not make recommendations 1) to take or not to take probiotics, 2) which probiotic strain(s) to take, and 3) how much probiotics to ingest for healthy people. If you are considering taking foods or supplements, you may need to self-educate as well as consult with a healthcare professional. As always, it is important to read the labels and weigh the potential risks against expected benefits, especially for people with weakened immune systems.

References

1. Food and Agriculture Organization of the United Nations; World Health Organization. Health and Nutritional Properties of Probiotics in Food Including Powder Milk with Live Lactic Acid Bacteria. In Proceedings of the Report of a Joint FAO/WHO Expert Consultation on Evaluation of Health and Nutritional Properties of Probiotics in Food Including Powder Milk with Live Lactic Acid Bacteria, Córdoba, Argentina, 1–4 October 2001; 1.

2. National Institutes of Health. Office of Dietary Supplements. Probiotics. https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/

3. Hasan and Yang. Factors affecting the composition of the gut microbiota, and its modulation. PeerJ. 2019. 7:e7502.

4. Zhang. Influence of foods and nutrition on the gut microbiome and implications for intestinal health. Int J Mol Sci. 2022, 23(17):9588.

5. Caffery et al. Our extended microbiome: The human-relevant metabolites and biology of fermented foods. Cell Metab. 2024. 36(4):684.

6. Leeuwendaal et a. Fermented foods, health and the gut microbiome. Nutrients. 2022,14(7):1527.

7. Bodke and Jogdand. Role of probiotics in human health. Cureus. 2022, 14(11):e31313.

8. Vera-Santander et al. Health benefits of consuming foods with bacterial probiotics, postbiotics, and their metabolites: A review. Molecules. 2023, 28:1230.

9. Ahire et al. Quality management of probiotics: Ensuring safety and maximizing health benefits. Current Microbiol. 2023, 81:1.

10. Jager et al. International Society of Sports Nutrition Position Stand: Probiotics. J Int Soc Sports Nutr. 2019, 16(1):62.

11. Sniffen et al. Choosing an appropriate probiotic product for your patient: An evidence-based practical guide. PLos One. 2018, 13(12): e0209205.

12. National Center for Complementary and Integrative Health. Probiotics: Usefulness and Safety. https://www.nccih.nih.gov/health/probiotics-usefulness-and-safety

13. Food and Drug Administration. Policy regarding quantitative labeling of dietary supplements containing live microbials: Guidance for Industry. https://www.fda.gov/media/115730/download

14. World Gastroenterology Organization. Probiotics and prebiotics. https://www.worldgastroenterology.org/UserFiles/file/guidelines/probiotics-and-prebiotics-english-2017.pdf 2017.

15. Salminen et al. The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nature Reviews. Gastroenterol. & Hepatol. 2021, 18:649.

16. International Scientific Association for Probiotics and Prebiotics. Deciphering a probiotic label.https://isappscience.org/wp-content/uploads/2019/04/Probiotic_labeling-_rev1029-1.pdf. 2017

This information is provided for your reference and you use at your own risk; you should rely on your medical professional for medical advice.