Intended for healthcare professionals

Education And Debate

Probiotics and prebiotics: can regulating the activities of intestinal bacteria benefit health?

BMJ 1999; 318 doi: (Published 10 April 1999) Cite this as: BMJ 1999;318:999
  1. George T Macfarlane, senior scientist,
  2. John H Cummings, senior clinical scientist.
  1. Medical Research Council Dunn Clinical Nutrition Centre, Cambridge CB2 2DH
  1. Correspondence to: Dr G T Macfarlane, Department of Molecular and Cellular Pathology, University of Dundee, Ninewells Hospital Medical School, Dundee DD1 9SY
  • Accepted 18 December 1998

The colonic microflora is important to health. The growth and metabolism of the many individual bacterial species inhabiting the large bowel depend primarily on the substrates available to them, most of which come from the diet. 1 2 This has led to attempts to modify the structure and metabolic activities of the community through diet—using probiotics and prebiotics. Probiotics are live microbial food supplements. The best known are the lactic acid bacteria and bifidobacteria, which are widely used in yoghurts and other dairy products (fig 1). These organisms are non-pathogenic and non-toxigenic,retain viability during storage, and survive passage through the stomach and small bowel. Prebiotics are non-digestible food ingredients which selectively stimulate the growth or activities, or both, of lactobacilli or bifidobacteria in the colon, thereby improving health.

Summary points

  • Microflora of the large intestine complete digestion through fermentation, protect against pathogenic bacteria and stimulate development of the immune system

  • Probiotics and prebiotics in the diet can modify the composition and some metabolic activities of the microflora

  • Probiotics are generally the live micro-organisms in foods such as yoghurts; they survive passage through the gut and temporarily bring the benefits of the normal gut flora

  • Probiotics have been used to treat or prevent diarrhoea and to improve symptoms in lactose intolerance

  • Prebiotics are non-digestible oligosaccharides that can stimulate selectively the growth of probiotic-like bacteria normally present in the gut

  • Many claims for the potential health benefits of prebiotics remain unproved

Fig 1

A selection of “bio” yoghurts available in supermarkets

The probiotic concept

Since probiotics do not permanently colonise the host, they need to be ingested regularly for any health promoting properties to persist. Most studies on probiosis have been observational rather than mechanistic, and thus the processes responsible for many probiotic phenomena are seldom explained. Some probiotics are members of the normal colonic microflora and are not …

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