Interactions between nutrition and the intestinal microflora.

Abstract

The human gut is well colonized by a wide variety of bacteria. In the industrial nations, the stomach and small intestine have a sparse flora protected by gastric acid and a highly propulsive motility. The flora of the small intestine increases along its length and particularly in the terminal ileum (Drasar & Hill, 1974). The large intestine has a very rich, mainly anaerobic, flora capable of fermenting carbohydrate and protein, and metabolizing a wide and diverse range of endogenous and exogenous molecules such as bile acids, fats and drugs. In the less-developed countries the small intestine has heavier populations of bacteria and these may be a factor in the higher occurrence of diarrhoea and malnutrition (Gorbach et al. 1970; Gracey, 1979). The interactions between nutrition and the intestinal microflora are complex. Bacteria in the gut may affect digestion and absorption, the products of bacterial fermentation may provide nutrients or affect the well-being of the host, but diet may also affect the survival and metabolism of the bacteria. The products of bacterial metabolism may be beneficial, for example butyrate which may have anti-neoplastic properties (Augeron & Laboisse, 1984), or they may be potentially harmful, for example bile acid metabolites which may be co-carcinogenic (Owen et af. 1987). The interaction between the intestinal microflora and nutrition begins at birth and changes with age and disease.