Most people are aware of the association between intestinal disease and pathogenic ("bad") bacteria, but what is less well known is the positive role of beneficial gut bacteria (probiotics) on our health and well-being.

These days, many of us spend hours worrying about what we look like on our outside when we should be spending more time thinking about our insides-especially what's going on in our digestive system. Our intestines digest the food we eat to provide the body with essential nutrients as well as removing waste material and toxins. Maintaining a healthy digestive system depends on keeping a balance among the billions of bacteria that live there. Scientific evidence is accumulating that upsetting the intestinal flora, as the gut bacteria are called, can lead to health problems such as indigestion, lowered immunity and susceptibility to diarrhoea. Stress, a poor diet, taking antibiotics or just tiredness may all upset the natural balance in the gut.

It has long been thought that the lower intestines, and in particular the colon, contributed little towards human nutrition. More recent studies, however, have indicated that colonic microflora appear to play a vital role in health and it appears that the role of the large bowel in health may have been underestimated.

Bacteria and gut health

The human colon contains over 200 species of bacteria and scientists are now studying the effects of various species and the role they appear to play in gut health.

Adults carry over 1 kg of gut bacteria and excrete their own weight in faecal bacteria every year. Some gut bacteria such as lactobacilli and bifidobacteria are thought to confer health-promoting properties. Early studies indicate that these good bacteria or 'probiotics', as they are called, may help to maintain a healthy balance of bacteria, stimulate gut immunity and help prevent colonisation by pathogenic organisms that cause stomach and intestinal disturbances and diarrhoea. Other studies are underway on the possible role of probiotics in helping to prevent allergies, improve bowel movements and aid in the formation of certain vitamins.

Probiotics and prebiotics

Work on probiotic foods has been underway for many years. These foods contain a live culture of microorganisms as a result of fermentation or through the addition of a culture. Examples of probiotic foods are some yoghurts, fermented dairy products and other foods such as fermented vegetables and fermented soy products. In addition, it is now possible to add probiotics to foods such as infant formulas (enriched with bifidobacteria) or prepare probiotic microorganisms as dietary supplements.

Two critical factors in the development of fermented milk products and other foods containing probiotics are the survival of the bacteria, both in the food or supplement and after digestion and the identity of the microbes used. These beneficial micro-organisms grow in air or in its absence and there are several barriers to their survival in the body, such as the acidity of the stomach, bile secretions and competition with the other resident gut bacteria. One approach that has been used to overcome these problems involves the addition of non-digestible food ingredients, such as dietary fibre-like food components, which are used by the beneficial bacteria as food for their growth. These food components are called 'prebiotics'.

A third approach, involves a combination of probiotics (the live bacteria) and prebiotics (the food components they live on). Innovative food products ("synbiotics") are now being developed to confer different health benefits depending on the specific micro-organisms (probiotics) used and their substrates(prebiotics) that are added as food ingredients.

While the area of pro- and prebiotics appears to offer a lot of potential, further research is needed to elucidate the mechanisms involved and the identification ofany health benefits offered by these substances and ingredients. It is anticipated that the next few years will see new developments in the understanding of human gut microbiology and the effects of a wide range of dietary constituents on health and well-being.

References

Gibson GR and Roberfroid MB. (1995) Dietary Modulation of the Human Colonic Microbiota: Introducing the Concept of Prebiotics. J.Nutr.,125:1401-12.

FOOD TODAY 12/2001