Probiotics

1. Introduction

What are Probiotics?

Probiotics are defined by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) as “live microorganisms which when administered in adequate amounts confer a health benefit on the host” [1, 2]. They are a diverse group of microorganisms, primarily bacteria and yeasts, that are naturally present in the human gut, often referred to as the gut microbiota.

The most common genera used in probiotic supplements and fermented foods are Lactobacillus and Bifidobacterium, but others like Saccharomyces, Streptococcus, and Bacillus are also used [3]. The specific health benefits are often strain-specific, meaning a benefit observed for one strain (e.g., Lactobacillus rhamnosus GG) may not apply to another.

Chemical/Botanical Basics

Probiotics are not single chemical compounds but living microbial cultures. They are typically identified by their genus, species, and an alphanumeric strain designation (e.g., Lactobacillus rhamnosus GG).

Mechanism of Action

Probiotics exert their beneficial effects through several key mechanisms within the gastrointestinal tract [1, 4]:

  1. Competitive Exclusion: They compete with pathogenic (harmful) bacteria for nutrients and adhesion sites on the intestinal wall, effectively “crowding out” the bad bacteria.
  2. Immune Modulation: They interact directly with the host’s immune cells in the gut-associated lymphoid tissue (GALT), helping to regulate the immune response and reduce inflammation.
  3. Gut Barrier Reinforcement: They can enhance the integrity of the intestinal epithelial barrier, reducing “leaky gut” and preventing the passage of toxins and pathogens into the bloodstream.
  4. Production of Bioactive Compounds: They ferment non-digestible carbohydrates (prebiotics) to produce beneficial metabolites, such as short-chain fatty acids (SCFAs)—like butyrate, propionate, and acetate—which are vital energy sources for colonocytes and play a role in systemic health.

2. Chemical Composition/Key Bioactive Roles

Probiotics are known for their metabolic activity, producing a variety of bioactive molecules that contribute to their health-conferring properties.

Key Bioactive Role Description Examples of Compounds Produced
SCFA Production Fermentation of dietary fiber to produce short-chain fatty acids, which nourish the colon lining and influence immune function. Butyrate, Acetate, Propionate
Enzyme Synthesis Production of digestive enzymes that aid in the breakdown and absorption of nutrients. Amylases, Peptidases, Lactase
Antimicrobial Production Synthesis of compounds that inhibit the growth of competing pathogens. Bacteriocins, Hydrogen Peroxide, Lactic Acid
Vitamin Synthesis Production of essential vitamins that can be absorbed by the host. Vitamin K, B-vitamins (e.g., Folate, B12)
Bile Salt Metabolism Deconjugation of bile salts, which may influence cholesterol metabolism. Deconjugated Bile Salts

3. Health Benefits

The health benefits of probiotics are extensive and well-supported by scientific literature, though they are often strain-specific.

Gastrointestinal Health

Probiotics are most widely recognized for their role in improving various gastrointestinal conditions:

  • Antibiotic-Associated Diarrhea (AAD): Meta-analyses consistently show that certain probiotic strains, particularly Lactobacillus rhamnosus GG (LGG) and Saccharomyces boulardii, are effective in preventing and treating AAD by restoring the balance of the gut microbiota [5].
  • Irritable Bowel Syndrome (IBS): Specific multi-strain and single-strain probiotics have demonstrated efficacy in alleviating global IBS symptoms, including abdominal pain, bloating, and flatulence [6]. For example, formulations containing Bifidobacterium longum have shown promising results in improving IBS symptoms [7].
  • Acute Infectious Diarrhea: Probiotics, especially LGG, can reduce the duration and severity of acute infectious diarrhea in children and adults [6].

Immune System Support

Probiotics play a crucial role in modulating the immune system, with the majority of immune cells residing in the gut:

  • Reduced Risk of Respiratory Infections: Regular probiotic consumption has been linked to a reduced incidence and duration of common upper respiratory tract infections, particularly in children, by enhancing immune defense mechanisms [8].
  • Allergy and Eczema: Some strains, such as Lactobacillus rhamnosus GG, have been studied for their potential to prevent or reduce the severity of atopic dermatitis (eczema) in high-risk infants [9].

Mental Health (Gut-Brain Axis)

Emerging research highlights the connection between the gut and the brain, known as the gut-brain axis:

  • Mood and Stress: Certain psychobiotics (probiotics with mental health benefits) like Bifidobacterium longum 1714 have been shown in clinical studies to improve sleep quality and reduce daytime dysfunction caused by sleepiness, suggesting a potential role in stress and mood regulation [10].

4. Dosage and Usage

Recommended Dosages

Probiotic dosage is measured in Colony-Forming Units (CFU), which represents the number of viable cells in a dose.

  • General Maintenance: For general digestive support and maintenance of a healthy gut flora, a daily dose of 1 billion to 10 billion CFU is commonly recommended.
  • Therapeutic Use: For specific conditions like AAD or IBS, higher doses are often used in clinical trials, sometimes ranging from 10 billion to 50 billion CFU or more per day [11].
  • Strain Specificity: It is crucial to note that the effective dose is highly dependent on the specific strain and the condition being treated. For instance, a 2015 analysis found that doses of ≥ 5 x 10⁹ CFU/day (5 billion CFU) were more effective in preventing AAD than lower doses [12].

Food Sources

Probiotics are naturally found in various fermented foods:

  • Yogurt: Contains live and active cultures, typically Lactobacillus bulgaricus and Streptococcus thermophilus. Look for labels that specify “live and active cultures.”
  • Kefir: A fermented milk drink, often containing a wider variety of bacterial and yeast strains than yogurt.
  • Sauerkraut and Kimchi: Fermented cabbage dishes that contain Lactobacillus species.
  • Kombucha: A fermented tea beverage containing a colony of bacteria and yeast (SCOBY).
  • Miso and Tempeh: Fermented soybean products.

5. Safety and Precautions

Probiotics are generally considered safe for healthy individuals and are well-tolerated. Side effects are typically mild and transient.

Side Effects

  • Mild Digestive Discomfort: The most common side effects are temporary gas, bloating, and mild digestive upset, especially when first starting supplementation [13].
  • Allergic Reactions: In rare cases, individuals may experience allergic reactions to ingredients in the supplement (e.g., dairy, soy, or yeast components).

Contraindications and Warnings

  • Immunocompromised Individuals: Probiotics should be used with extreme caution in individuals who are critically ill, have a severely compromised immune system (e.g., those with central venous catheters, post-surgery, or on immunosuppressive drugs), or have underlying severe illnesses. In rare instances, there is a risk of developing bacteremia or fungemia (infection in the bloodstream) from the probiotic organism itself [13].
  • Infants with Short Bowel Syndrome: Caution is advised, as rare cases of infection have been reported in this population.

Drug Interactions

  • Antibiotics: Antibiotics are designed to kill bacteria and can therefore kill probiotic bacteria. To maximize the benefit of a probiotic supplement, it is generally recommended to take the probiotic at least 2-3 hours before or after taking an antibiotic [14].
  • Antifungals: For yeast-based probiotics like Saccharomyces boulardii, antifungal medications (e.g., ketoconazole, nystatin) may reduce their efficacy.
  • Immunosuppressants: Individuals taking immunosuppressive drugs should consult a healthcare professional before taking probiotics, as the interaction could theoretically increase the risk of infection.

6. References

  1. Hill, C., et al. (2014). The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology, 11(8), 506–514. https://www.nature.com/articles/nrgastro.2014.66
  2. Reid, G. (2016). Probiotics: definition, scope and mechanisms of action. Best Practice & Research Clinical Gastroenterology, 30(1), 17–25. https://www.sciencedirect.com/science/article/abs/pii/S1521691815001651
  3. Latif, A., et al. (2023). Probiotics: mechanism of action, health benefits and their applications in food and pharmaceuticals. Frontiers in Microbiology, 14. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1216674/full
  4. Sharifi-Rad, J., et al. (2020). Probiotics: Versatile Bioactive Components in Promoting Human Health—An Overview. Molecules, 25(20), 4880. https://pmc.ncbi.nlm.nih.gov/articles/PMC7560221/
  5. Steele, C. (n.d.). Lactobacillus rhamnosus GG: A Review of Clinical Use and Efficacy. NMI Health. https://www.nmi.health/lactobacillus-rhamnosus-gg-a-review-of-clinical-use-and-efficacy/
  6. Wilkins, T., et al. (2017). Probiotics for Gastrointestinal Conditions: A Summary of the Evidence. American Family Physician, 96(3), 170–178. https://www.aafp.org/pubs/afp/issues/2017/0801/p170.html
  7. Mills, S., et al. (2023). Efficacy of Bifidobacterium longum alone or in multi-strain formulations for the management of gastrointestinal disorders: a systematic review. Gut Microbes, 15(1), 2189914. https://pmc.ncbi.nlm.nih.gov/articles/PMC10012958/
  8. NIH National Center for Complementary and Integrative Health (NCCIH). (n.d.). Probiotics: What You Need To Know. https://www.nccih.nih.gov/health/probiotics-what-you-need-to-know
  9. Kopp, M. V., et al. (2008). Effect of Lactobacillus rhamnosus GG on the development of atopic disease in infants and children: a meta-analysis. Allergy, 63(11), 1321–1328. https://pubmed.ncbi.nlm.nih.gov/18847424/
  10. Patterson, E., et al. (2024). Bifidobacterium longum 1714 improves sleep quality and reduces daytime dysfunction caused by sleepiness in healthy adults: a randomized, double-blind, placebo-controlled trial. Scientific Reports, 14(1), 4872. https://www.nature.com/articles/s41598-024-53810-w
  11. Office of Dietary Supplements (ODS), National Institutes of Health (NIH). (2025). Probiotics – Health Professional Fact Sheet. https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/
  12. Hempel, S., et al. (2012). Probiotics for the prevention and treatment of antibiotic-associated diarrhea: a systematic review and meta-analysis. JAMA, 307(18), 1959–1969. https://jamanetwork.com/journals/jama/fullarticle/1151502
  13. NCCIH. (n.d.). Probiotics: Usefulness and Safety. https://www.nccih.nih.gov/health/probiotics-usefulness-and-safety
  14. WebMD. (n.d.). Adult Probiotic oral: Uses, Side Effects, Interactions, Warnings, and Patient Education. https://www.webmd.com/drugs/2/drug-163888/adult-probiotic-oral/details

Category: Probiotic