Nutrition and gastrointestinal disorders.

The gastrointestinal tract, including the liver and pancreas, is a complex system whose function is to process a wide range of nutrient and other products enabling their absorption as well as detoxification and excretion. During the process, food is converted into energy and into other substances that are used by cells throughout the entire body. Many diseases can affect the various organs of the gastrointestinal (GI) system and diet plays a relatively minor role in the onset of such GI diseases. Recently it has become clear that glutamine, a 'non-essential' amino acid, is important in the maintenance of intestinal mucosal metabolism, structure and function. Dietary fibre has complicated properties including trophic effects on intestinal mucosa, volatile fatty acid production, alteration of bacterial flora and faecal bacterial mass and change in faecal bile acids. Gastrointestinal disease many result from deficiency or excess of specific nutrients in normal individuals. In allergic or susceptible subjects, diseases such as food allergy, disaccharidase intolerance and gluten sensitive enteropathy may occur with intake of normal daily requirements. In genetically susceptible individuals, specific nutrients have been linked, based on epidemiological studies and animal experimentation, to carcinoma of the stomach (high starch, high nitrate foods and smoked meats) and colon (low fibre, high fat, low vitamin A). A recent Australian multi-centre polyp prevention project has recruited subjects with adenomatous polyps cleared at colonoscopy. Subjects were randomised to receive high fibre, low fat, b -carotene or a combination of these and compared to an unchanged control group at 2-yearly follow up colonoscopy. Low fat and high fibre were not protective against polyp development; however, b -carotene ingestion was associated with an increased risk. Duodenal ulcer disease is multifactorial with gastric acid and H. pylori induced gastroduodenitis playing important aetiological roles. Protection is afforded to individuals with a higher unsaturated fatty acid and lower refined sugar intakes. Treatment of gastrointestinal disease may require dietary modifications or, if the gut is not functioning adequately, nutritional support via the parenteral route. In subjects with inflammatory bowel disease and short gut syndrome replacement of specific nutrients may be required particularly calcium, magnesium, zinc, iron, and vitamins B12, folate, D and A. Controversy still exists as to the role of parenteral and enteral nutrition as primary therapy for inflammatory bowel disease.