What are Probiotics?

There are millions of bacteria naturally and necessarily present in the human gut (colon; large intestine). The population of different types of bacteria are called the microbial flora of the colon, and we know of many useful functions they carry out which support health. The bacteria ferment the small amount of starch that resists digestion in the small intestine to produce ‘short-chain fatty acids’; these are an energy supply for the body and also keep the cells of the colon wall healthy. The microbial flora also acts as a physical barrier to protect the colon from pathogenic (disease-causing) bacteria.

The bacteria in the colon described as being beneficial are mainly lactobacilli and bifidobacteria, and the well-being of the ‘host’ is supported when these prevail over other bacteria that may be potentially harmful. The concept of supporting the balance of microbial flora to favour benign bacteria has led to the development of ‘colonic foods’ described as probiotics and prebiotics.

Probiotics are live microbial supplements that have been shown to survive transit through the upper digestive system, and may beneficially colonise the microbial flora of the large intestine. Such benign digestion-resistant bacteria have been added to many popular and now widely-available ‘functional’ foods such as yogurts and milk-based drinks. The Japanese brand Yakult is the earliest and best-known brand in this category.

Prebiotics are types of carbohydrates (oligosaccharides) that cannot be digested in the small intestine: they reach the colon where they selectively support the growth of benign bacteria already present. In this way, the healthier bacteria in the colonic microflora are stimulated and are given a competitive advantage over other types of bacteria present. Some foods naturally contain small amounts of oligosaccharides (leek, asparagus, chicory, Jerusalem artichoke, bananas, oats), but higher levels are usually found in functional foods fortified with prebiotic ingredients. Human breastmilk can be considered the original functional food; it contains many factors that support  bifidobacteria growth in the colon, and this may protect the infant from gastrointestinal problems.

The balance of colonic microflora is know to be affected by the use of antibiotics, and may also be adversely influenced by diets low in carbohydrate, ageing and some disease conditions. The use of probiotics/prebiotics have been investigated to support colonic health in inflammatory conditions such as Crohn’s disease and inflammatory bowel disease. Some studies also support benefits for the protection from, and the treatment of diarrhoea. Research is currently investigating other possible health effects.

March 2006