• Probiotics are defined by the World Health Organization as “live microorganisms, which when administered in adequate amounts, confer a health benefit to the host.”
  • The presence of “live cultures” does not make a product a probiotic. The microorganism has to be present in adequate amounts to provide specified health benefit, which can vary, depending on the microorganism. The optimal dosing varies with probiotic product, indication, and host.
  • Specific probiotic strains are generally regarded as safe. The Center for Food Safety and Applied Nutrition (CFSAN) provides guidelines for the manufacture of probiotic products, but clinicians must carefully evaluate the probiotic agent selected.
  • Levels of evidence to support use of a probiotic depend on the formulation and indication (food, supplement, or drug) and the consumer (clinician, patient, healthy individual, and regulatory authority).
  • Several formulations of probiotic products are available both in single-strain and multistrain preparations:
    • Probiotic organisms may be consumed as fermented dairy products or as supplements in the form of a capsule, tablet, liquid, or powder formulation.
  • Commonly used probiotic supplements contain single organisms, including the following strains:
    • Bifidobacterium bifidum strain YIT 4002
    • Lactobacillus rhamnosus ATCC 53103
    • Lactobacillus delbrueckii subsp. bulgaricus
    • Streptococcus salivarius subsp. thermophilus
  • Yeast, including Saccharomyces boulardii, is an alternative to bacterial probiotic formulations.
  • Multistrain probiotics incorporate a combination of organisms in varying quantities.


  • Probiotics are hypothesized to exert their primary effects on the gut by reestablishing the intestinal microbiota balance, competing for receptor sites in the intestinal lumen, and competing with pathogens for nutrients.
  • The proposed immunomodulatory functions of probiotics include enhancing host immune defenses via strengthening tight junctions between intestinal enterocytes, increasing immunoglobulin A production, stimulating cytokine production, and producing substances (e.g., arginine, glutamine, and short-chain fatty acids) thought to secondarily act as protective nutrients.

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