How do probiotics work?

Probiotics are beneficial bacteria that colonise the intestinal tract and act to promote the efficient functioning of digestion, help prevent digestive upsets and stimulate and maintain the natural immunity of the body. Probiotic bacteria are normal inhabitants of the intestines and are found in the healthy gut of all humans. Probiotics have been shown to work by the following mechanisms:

Competition for nutrients
Within the gut, beneficial as well as pathogenic microorganisms will be utilising the same types of nutrients. Thus there will be a general competition for these nutrients to grow and reproduce. The more the gut is flooded with beneficial microorganisms, the more competition is created between beneficial and pathogenic microorganisms.

Competition for adhesion sites
Adhering to adhesion sites along the wall of the gut is an important colonisation factor. Many intestinal pathogens rely on adhesion to the gut wall to prevent them being swept away by peristalsis of food along the intestinal tract.

An important function of these probiotic bacteria is to prevent or limit the growth and colonisation of potentially pathogenic bacteria such as E. coli, Salmonella, Listeria, Campylobacter and Clostridia within the gut. These pathogenic bacteria are known to cause major disturbances within the gut, thus preventing efficient digestion and nutrient absorption within the gut, and may result in diarrhoea or vomiting.

Where the gut microflora is well balanced, the beneficial microorganisms colonised within the gut can hence help to reduce the risk of pathogenic challenge.

Stimulation of immunity
Probiotics have been shown to ensure the optimum microflora balance in order to stimulate and maintain the natural immune system of the host. These enhanced immune effects help to prevent illness when probiotics are used regularly.

Direct antimicrobial effect
This can either operate via bacteriocins, which are known to be produced by many species of lactic acid bacteria, or by the production of organic acids, which can either have a direct effect or operate by reducing the pH of the gut.

Improvement in digestion
Probiotic microorganisms act like, and add to, the healthy microflora by producing enzymes that aid the breakdown of polysaccharides such as carbohydrates so as to allow the absorption of the energy obtained from these nutrients by the gut. The microflora also ferments the carbohydrates which have not been digested in the upper gut and produces vitamins that supply a secondary source to the host.