World Health Organization (WHO) defines “probiotics” as “live microorganisms that, when administered in adequate amounts, confer a perceived health benefit on the host”. These intentionally ingested microorganisms consist mainly of bacteria but also include yeasts. Products containing dead microorganisms and those made by microorganisms are, by definition, not probiotics.
Probiotics (Greek pro, for, and bios, life) confer various benefits especially to individuals who experience major changes in their normal microflora due to disease, surgery, or other medical treatments, or whose normal microflora changes for other reasons, such as poor diet. Oral administration of probiotic organisms reestablish the natural balance of gastrointestinal flora and return the host to normal health and nutrition.
Probiotic microorganisms are host-specific; thus a strain selected as a probiotic in one animal may not be suitable in another species. Probiotics are subcategorized into probiotic drugs, probiotic foods (e.g., foods, food ingredients, and dietary supplements), direct-fed microbials (probiotics for animal use), and designer probiotics (genetically modified probiotics).
Probiotics should not be confused with prebiotics which are food ingredients, typically complex carbohydrates (mostly consisting of nonstarch polysaccharides and oligosaccharides) that escape digestion in the upper gastrointestinal tract and are available for microorganisms living in the colon.
Most prebiotics are used as food ingredients in chocolates, biscuits, cereals, spreads, and dairy products. Commonly known prebiotics are:
- Breast milk oligosaccharides
The prebiotic oligofructose is found naturally in many foods, such as wheat, onions, bananas, honey, garlic, and leeks. Oligofructose can also be isolated from chicory root or synthesized enzymatically from sucrose. Inulin is a prebiotic fiber that occurs naturally in asparagus, garlic, onions, wheat, garlic, leeks, chicory, oats, soybeans, and Jerusalem artichokes.
Galacto-oligosaccharides which are mainly used in infant milk formula are made up of plant sugars linked in chains. They are found naturally in dairy products, beans, and certain root vegetables. Lactulose is a man-made sugar that contains two naturally occurring sugars, galactose, and fructose. Lactulose is produced industrially by isomerization of lactose via a 1,2-enediol intermediate.
Health Benefits of Prebiotics
The use of both prebiotics and/or probiotics is intended to influence the gut environment for the benefit of human health and their beneficial effects extend beyond the gut. Fermentation of oligofructose in the colon results in a large number of physiologic effects, including:
- Increasing the number of bifidobacteria in the colon
- Increasing calcium absorption
- Increasing fecal weight
- Shortening gastrointestinal transit time
- Possibly lowering blood lipid levels
Prebiotics selectively stimulate the growth of selective bacterial genera such as bifidobacteria and lactobacilli in the colon. The increase in colonic bifidobacteria benefits human health by producing digestive enzymes, vitamins, reducing blood ammonia levels, and inhibiting potential pathogens. Lactulose is a synthetic disaccharide used as a drug for the treatment of constipation and hepatic encephalopathy.
Commercial products containing both prebiotic sugars and probiotic organisms are often called “synbiotics.” Synbiotics are appropriate combinations of prebiotics and probiotics and exert both a prebiotic and probiotic effect.
Probiotics vs. Antibiotics
The term “probiotic” literally means “for life” and “antibiotic” literally means “opposing life” are two opposing categories of supplements or drugs. Antibiotics (Greek anti, against, and bios, life) are used to prevent and treat infections caused by pathogenic bacteria whereas probiotics (Greek pro, for, and bios, life) are used to replenish good bacteria.
For example, during the course of antibiotics treatment, good bacteria of the gut are also wiped out, taking probiotics helps to restore the gut microbiome, thus restoring the healthy state of the gut.
A probiotic should contain a number of viable cells greater than 106 to 108 per dose to be efficacious. Seven microorganisms most often used in probiotic products are Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus.
These beneficial microorganisms are naturally present in fermented foods (such as yogurt, kefir, kimchi, etc), may be added to other food products, and also available as dietary supplements or as drugs. Probiotic microorganisms from commercial providers come in a variety of forms, including powders, pills, liquid suspensions, and food products.
Microorganisms selected for probiotic use should exhibit the following characteristics:
- Adhere to the intestinal mucosa of the host
- Be easily cultured
- Be nontoxic and nonpathogenic to the host
- Exert a beneficial effect on the host
- Produce useful enzymes or physiological end products that the host can use
- Remain viable for a long time
- Withstand HCl in the host’s stomach and bile salts in the small intestine
Health Benefits of Probiotics
Numerous clinical trials have proven the health benefits of probiotics but the exact mechanisms of the health benefits are not fully understood. Gut health is the most important target for probiotics. Prevention and treatment of different forms of diarrhea is one of the most successful and best-documented health benefits of probiotics.
Alterations in the composition of the intestinal microbiome have been associated with infections in the gastrointestinal tract, inflammatory bowel disease (IBD), and irritable bowel syndrome (IBS). Growing evidence indicates that probiotics may be effective in the treatment of specific clinical IBD and IBS conditions but large trials are necessary before doctors can prescribe particular probiotics confidently on a routine basis as therapeutic agents.
Proven potential benefits of probiotics include:
- Anticarcinogenic activity
- Control of intestinal pathogens
- Improvement of lactose use in individuals who have lactose intolerance
- Reduction in the serum cholesterol concentration
- Reduction of the risk of antibiotic-induced diarrhea
References and further readings
- Aragon, G., Graham, D. B., Borum, M., & Doman, D. B. (2010). Probiotic Therapy for Irritable Bowel Syndrome. Gastroenterology & Hepatology, 6(1), 39–44.
- Conly, J. M., & Johnston, L. B. (2004). Coming full circle: From antibiotics to probiotics and prebiotics. The Canadian Journal of Infectious Diseases & Medical Microbiology, 15(3), 161–163.
- Hemarajata, P., & Versalovic, J. (2013). Effects of probiotics on gut microbiota: Mechanisms of intestinal immunomodulation and neuromodulation. Therapeutic Advances in Gastroenterology, 6(1), 39–51. https://doi.org/10.1177/1756283X12459294
- Office of Dietary Supplements—Probiotics. Retrieved June 28, 2021, from https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/
- Probiotics: What You Need To Know. NCCIH. Retrieved June 28, 2021, from https://www.nccih.nih.gov/health/probiotics-what-you-need-to-know
- Venugopalan, V., Shriner, K. A., & Wong-Beringer, A. Regulatory Oversight and Safety of Probiotic Use—Volume 16, Number 11—November 2010—Emerging Infectious Diseases journal—CDC. https://doi.org/10.3201/eid1611.100574