Malnutrition is common in chronic alcoholics, although its severity may depend on the social characteristics of the patient group under study and their severity of alcohol dependence. General malnutrition is often reflected in body weight loss, mainly of adipose and muscle tissue. This loss of nutritional reserves is partly due to inadequate protein intake in the face of continued alcohol ingestion. However, there is also evidence that ethanol is relatively ineffective as a source of calories, in spite of its high theoretical calorific value. An increased metabolic rate and tissue oxygen consumption following alcohol ingestion, without parallel increases in phosphate bond energy production or anabolic processes demonstrate the poor value of ethanol as an alternative calorie source to carbohydrate, fat or protein. This situation of nutritional imbalance is often compounded in chronic alcoholics by the effects that ethanol has on gastrointestinal function. These include increased mucosal permeability which may lead to 'leakage' of nutrients from the blood to the gut lumen, increased gut motility with increased transit times, and impaired salt and water absorption. Alcohol inhibits absorption of vitamins and nutrients by active transport processes, an effect that may be crucial in precipitating specific nutrient deficiencies (e.g. thiamine) in the alcoholic, in addition to the role of reduced dietary intake of vitamins and minerals in alcoholics that also contributes to such deficiency states. The end result may be severe functional impairment and tissue damage in other organs, notably the liver and the brain, as a consequence of specific vitamin and nutrient deficiencies arising in chronic alcoholics by these mechanisms.