Probiotics, prebiotics and symbiotics

What are they

• Probiotics. The definition of probiotics internationally accepted today is the one developed by a group of experts from the two agencies of the Food Organization of the United Nations (FAO) and Health Organization (WHO): “live microorganisms that, ingested in adequate quantities (through specially enriched foods or in the form of supplements), are able to exert beneficial functions for the body”.
• Prebiotics. These are some non-digestible substances of food origin (mostly belonging to the chemical class of sugars) which, if ingested in adequate quantities, are able to selectively promote the growth and / or activity of one or more microorganisms among those already present in the intestinal bacterial flora or among those simultaneously administered as probiotics.
• Symbiotic. They are those foods or supplements that simultaneously contain both probiotic microorganisms and substances with prebiotic properties.

How they work

Probiotics. The main mechanisms through which probiotics can produce positive effects are:

• modulation of immune functions at the level of the intestinal mucosa (inhibition of the inflammatory response, activation of defense mechanisms);
• contrast/competition action against other microorganisms that can cause infections (pathogens);
• elimination of harmful substances (toxins, free radicals) present in the intestinal lumen.

Prebiotics. Their transformation by microorganisms of the intestinal flora produces molecules (short-chain fatty acids) that have various favorable effects:

• stimulation of the growth of beneficial microorganisms (especially bifidobacteria);
• reduction in the growth of pathogenic bacteria;
• optimization of intestinal absorption of micronutrients.

What are they?

The scientific literature gradually describes an increasing number of microorganisms that can be considered probiotics.

At the moment most of the bacterial strains with proven probiotic efficacy and safety of use belong to the genera Lactobacillus and Bifidobacterium, but some strains of Escherichia coli and yeasts of the genus Saccharomyces are also used.

It has also been shown that individual bacterial strains (populations of bacteria belonging to the same species but with minimal differences between them) have specific probiotic characteristics and that for each type of microorganism the amount to be administered to obtain beneficial effects varies considerably depending on the strains.

For this reason, supplements containing probiotics must report, for each type of microorganism present, the name of the genus and species, the code that identifies the strain to which it belongs (for example Lactobacillus rhamnosus GG, Bifidobacterium animalis DN 173 010 etc.) and the concentration of viable microorganisms (which must remain so until the shelf life of the product) normally expressed in credits per milliliter or per dose.

It should be emphasized that foods enriched with probiotics (which do not report their concentrations) do not always contain a sufficient number of microorganisms to guarantee their effectiveness.

What they do

The positive effects of probiotics best documented are those on the gastrointestinal system, where they have proven useful as adjuvants in the treatment of a series of pathological conditions: diarrhea associated with the intake of antibiotics, infectious gastroenteritis, childhood enterocolitis, irritable bowel syndrome, ulcerative colitis, Helicobacter pylori infection, malabsorption.

Some studies have also demonstrated the potential efficacy of probiotics in the prevention or symptomatic reduction of allergic and infectious respiratory diseases and urinary and genital infections, due to their immunomodulation activity.

Not yet sufficiently documented are other beneficial effects that are thought to be attributed to probiotics, such as the reduction of cholesterol levels and the prevention of colorectal cancers.

Safety of use

The microorganisms used as probiotics must meet a number of efficacy and safety requirements:

• be of safe use in humans;
• not be carriers of acquired and/or transmissible antibiotic resistance;
• be able to persist and multiply in the human intestine;
• be active and viable in sufficient quantities to justify any beneficial effects observed in efficacy studies.

With regard to safety, a list of bacterial species supposedly qualified as safe has been drawn up by the European Food Safety Authority (EFSA).