Role of Probiotics in Human Health

Authors

  • Mária Figler PTE EFK Humán Táplálkozástudományi és Dietetikai Intézet Pécs (Pécs University, Institute of Human Nutrition and Dietetics)
  • Regina Rab PTE EFK Humán Táplálkozástudományi és Dietetikai Intézet Pécs (Pécs University, Institute of Human Nutrition and Dietetics)
  • Katalin Bonyárné Müller PTE EFK Humán Táplálkozástudományi és Dietetikai Intézet Pécs (Pécs University, Institute of Human Nutrition and Dietetics)

Abstract

The bacterial flora of the intestinal tract has a number of functions, most of which are beneficial to the host. Despite the discovery of antibiotics and the subsequent frequent additions to our antimicrobial armamentarium, patients are still dying from infections. This may be due to the fact that treatment is sometimes started too late. However, in the last few years the failure of antibiotic treatment has been attributed more and more often to resistance. The idea of restrained antibiotic use has often been suggested but, until now, without success. As a result, we may be faced with multiple drug resistance of bacteria and fungi without any effective antibiotic therapy left when treating infections in the foreseeable future. In some countries such a situation already exists in a number of hospitals. It means that, for for the treatment of bacterial and fungal infections, antibiotics will have to be replaced by a fundamentally different method of treatment as soon as possible. Such alternative treatment could result from having more information that is presently available about interactions between the intestinal microflora and the host. Scientific interest in the importance of the intestinal microflora in human health has increased significantly over the last ten to twenty years. As far as the advantages for the host are concerned, it has been established that a healthy intestinal microflora exhibits the following effects: - Stimulation of the immune system; - Increasing resistance to the settlement of pathogenic bacteria; - Digestion of hard-to-digest food components by the production of short-chain and other fatty acids; - Synthesis of vitamin K. It has also been established that, under certain circumstances, the normal intestinal microflora may be disturbed and colonisation by unwalted bacteria may take place in the bowel. For example, this may happen during treatment with oral antibiotics, food poisoning with pathogenic bacteria, viral infections, stress, reduced bowel motility, and lack of gastric acid. The latter two factors play an important role in bacterial overgrowth in the small intestine, which may lead to incomplete digestion of food. Only in the last few years has it been realised that the metabolic activity of the intestinal microflora can, under certain conditions promote the formation of substances that encourage the development of bowel cancer. Knowledge about nutritional factors that may positively influence the composition and activity of the intestinal micriflorais therefore very important. These food components may be divided into theree categories, the first and second being the most important: 1. Nutrients (substrates) for the intestinal microflora, also called „prebiotics”. 2. Living lactic acid bacteria with a beneficial effect on the intestinal microflora, the socalled „probiotics”; 3. Synergistic combinations of 1 and 2, also called „synbiotics”. Prebiotics A balanced population of intestinal microflora needs to have a sufficient supply of substrates (most importantly carbohydrates) to be able to grow. Part of this carbohydrate supply is bowel mucus and the rest consistsof indigestible or only partially digestible carbohydrates or compounds derived from them. After consumption, these substances end up, wholly or partly, in the large bowel. There they are broken down further by bacteria into substances that are beneficial to humans lactic and propionic acids, acetate and butyrate. This results in fall in the pH of the bowel contents while, at the same time, gases are formed (carbon dioxide, hydrogen, and methane). Dietary fibres are important substrates (specifically their water-soluble fraction) including difficult-to-digest starch fractions (amylose), pectins, indigestible oligosaccharides (e.g. inulin), and substances like lactulose, lactitol and other sugar alcohols. The pH influences the composition of the intestinal microflora and a reduction in pH in combination with the volatile fatty acids that have been formed will protect against the settlement of pathogenic bacteria. It is assumed that the presence of adequate amounts of bifidobacteria indicates that the intestinal microflora is in a balanced and healthy state. Any disturbance in the normal flora is accompanied by disappearance of the (anaerobic) bifidobacteria and an increase in aerobic strains. Probiotics Probiotics are living organisms that , after being ingested by humans or animals, exert beneficial or health-enhancing effects by improving the characteristics of the intestinal microflora. They are, for instance, used in fermented dairy products. The most important are lactic acid bacteria that (by resistance to gastric acid and bile) are able to survive passage through the stomach and small intestine. Several strains of Lactobacillus acidophilus, Lactobacillus casei and certain bifidobacteria posses this characteristic. The information that is presently available may be summarised as follows: - It is certain that various lactic acid bacteria, such as the bacteria present in yoghurt can assist in the digestion of milk sugar because they themselves have lactase activity. This is part of the reason why people who have a lactase deficiency are more able to tolerate yoghurt than milk. Although yoghurt bacteria are rarely able to survive passage through the intestines, their lactase will stay active long enough to assist in the breakdown of milk sugar in the bowel. - There is no doubt that certain lactic acid bacteria can influence the immune system through interaction with the lymphoid tissue in the bowel (e.g. activating macrophages and increasing antibody production after vaccination). - Studies in animals have shown that the growth of certain tumours may be inhibited by administration of probiotics. - Although certain lactic acid bacteria have bile salt hydrolase activity and therefore, might be able to increase the secretion of bile salts in the faeces and also decrease serum cholesterol levels. - It has been found that in humans the duration of certain kinds of diarrhoea can be limited by the intake of Lactobacillus casei or specific bifidobacteria. This is the case for diarrhoes casued by antibiotic treatment, rotavirus and the so-called travellers diarrhoea. - It has been show in animal models that probiotics can increase the colonisation resistance to enteropathogenic bacteria. - Several animals studies and tests in humans have demonstrated that probiotics have a positive effect by reducing the activity of certain enzymes that may be involved in the development of substances that increase the risk of cancer. It may be possible to reduce the risk of small bowel cancer in this way.

Published

2004-02-15

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Section

Articles