Nutritional demands in acute and chronic illness.

Common to both acute and chronic disease are disturbances in energy homeostasis, which are evidenced by quantitative and qualitative changes in dietary intake and increased energy expenditure. Negative energy balance results in loss of fat and lean tissue. The management of patients with metabolically-active disease appears to be simple; it would involve the provision of sufficient energy to promote tissue accretion. However, two fundamental issues serve to prevent nutritional demands in disease being met. The determination of appropriate energy requirements relies on predictive formulae. While equations have been developed for critically-ill populations, accurate energy prescribing in the acute setting is uncommon. Only 25-32% of the patients have energy intakes within 10% of their requirements. Clearly, the variation in energy expenditure has led to difficulties in accurately defining the energy needs of the individual. Second, the acute inflammatory response initiated by the host can have profound effects on ingestive behaviour, but this area is poorly understood by practising clinicians. For example, nutritional targets have been set for specific disease states, i.e. pancreatitis 105-147 kJ (25-35 kcal)/kg; chronic liver disease 147-168 kJ (35-40 kcal)/kg, but given the alterations in gut physiology that accompany the acute-phase response, targets are unlikely to be met. In cancer cachexia attenuation of the inflammatory response using eicosapentaenoic acid results in improved nutritional intake and status. This strategy poses an attractive proposition in the quest to define nutritional support as a clinically-effective treatment modality in other disorders.