There have been substantial changes in the nutritional management of many diseases in the last 20 years, which have been accompanied by a growing recognition of its importance. Many of the changes in clinical nutrition have been associated with the introduction of standards, clinical audit and the implementation of evidence-based practice, which has led to a re-evaluation of some established dietary interventions using a hierarchy-of-evidence approach. Although there are few randomised controlled trials on which to base such work, the examination of other, often less-robust, evidence has led to some traditional dietary interventions being modified. Examples in gastroenterology include the use of low-fat diets in gall bladder disease and the restriction of protein in hepatic encephalopathy, where the current evidence suggests that neither should be used routinely in clinical practice. Where therapeutic dietary restrictions are required, as with low-Na diets in ascites, there is very little information on how these restrictions influence total nutrient intake and, if intake is impaired, how the detrimental effects of an inadequate intake should be balanced with the therapeutic effects of restriction. Studies are required to ensure that nutritional interventions are not only effective but also free from undesirable side effects. The mode and timing of the delivery of nutritional support has also been re-evaluated and the benefits of early enteral feeding have been recognised. The delivery of dietary advice is a new area that is being considered, with practitioners in clinical nutrition using behaviour-change skills to facilitate optimum nutrition rather than simply providing patients with advice. For such developments to continue in clinical nutrition it is essential that all practice should be systematically evaluated and, where necessary, modified in the light of sound current research findings, and that gaps in our present knowledge base are identified and addressed.