Prebioticos, Probioticos Simbioticos

International Dairy Journal 9 (1999) 53}61

Prebiotics, probiotics and human gut microbiology
Laura J. Fooks *, Roy Fuller , Glenn R. Gibson
Department of Food Science and Technology, The University of Reading, Whiteknights, Reading, UK Russet House, Ryeish Green, Reading, UK

Abstract Because of its resident microbiota, the human colon is one of the body's most metabolically activeorgans. Gut bacteria predominantly ferment undigested food materials. The nature of the fermentation may have di!erent health consequences. For example, the end products of carbohydrate metabolism are benign, whilst proteolytic metabolites may be toxic. The use of diet to fortify certain gut #ora components is a popular current aspect of functional food sciences. In this context probiotics, prebioticsand synbiotics all have a signi"cant role. Probiotics are live microbial additions to the diet; prebiotics are foodstu!s that have a selective metabolism in the hindgut, whilst synbiotics are combinations of the two approaches. It has been demonstrated that each of these dietary intervention routes can have an e!ect on the gut #ora &balance'. Whilst the real health advantages remain elusive, theuse of gut micro#ora management has a number of potentially very important e!ects with resistance to pathogens, e!ects on gut tumours and reduction in blood lipids holding much promise. The advent of molecular tools into gut microbiology, now o!er the means to more fully explore the gut biodiversity as well as reliably track changes in response to diet. The near future will determine whether thefull potential of probiotics, prebiotics and synbiotics can be realised. 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Prebiotic; Probiotic; Synbiotic; Colonic bacteria

1. Human gastrointestinal bacteriology Functionally, the human colon undertakes a number of important physiological activities. For example, enterocytes actively transport sodium and chloride, with absorptionoccurring via a parallel mechanism of sodium}hydrogen and chloride}bicarbonate exchanges. Potassium enters the lumen via enterocytes, utilising an active secretory pathway. The mucosa is rich in carbonic anhydrase and in endocrine cells which produce hormones and neurotransmitters. As such, physiologically and endocrinologically, the human colon has major importance. However, another extremelysigni"cant metabolic trait is mediated by gut bacteria. In the human gastrointestinal tract, there exists variability in bacterial numbers and populations between the stomach, small intestine and colon. The total bacterial count in gastric contents is usually

* Corresponding author. Tel.: #44-11-89357033; fax: #44-1189267917. E-mail address: laura.fooks@bbsrc.ac.uk (L.J. Fooks)

below 10 per g,with numbers in the small intestine ranging from about 10 per ml of contents to about 10}10 at the terminal ileum (Gorbach, Nahas & Lerner, 1967). In comparison to other regions of the gastrointestinal tract, the human large intestine is a complex, heavily populated and diverse microbial ecosystem. Bacterial numbers in the human large intestine are in the region of 10}10 for every gram ofgut contents (Cummings & Macfarlane, 1991). The colonic micro#ora is capable of responding to anatomical and physicochemical variations that are present. The right or proximal colon is characterised by a high substrate availability (due to dietary input), a pH of around 5.5}6.0 (from acids produced during microbial fermentation) and a more rapid transit than the distal region. The left, or distal,area of the colon has a lower concentration of available substrate, the pH is approximately 6.5}7.0 and bacteria grow more slowly. The proximal region tends to be a more saccharolytic environment than the distal gut, the latter having higher bacterial proteolysis. Several hundred di!erent species of bacteria are thought to be present in the large intestine. Gram negative rods belonging to the...