The concept of permissive underfeeding is based on the rationale that higher nutrient intake is detrimental from a metabolic and functional perspective. Animal studies have demonstrated improved morbidity and mortality with energy restriction. Studies with obese patients have demonstrated that a hypocaloric feeding regimen can promote nitrogen equilibrium and minimize negative nitrogen balance without causing weight loss. In critically ill patients, permissive underfeeding with parenteral nutrition has not been well studied, although some benefit is apparent. In enterally fed patients, more research exists but the data are not generated from prospective controlled trials. Studies of enterally supported patients demonstrate an association between higher caloric intake and decreased morbidity and mortality. Despite limited research, provision of reduced energy intake in critically ill patients and obese patients may result in improved metabolic control, reduce the detrimental effects of overfeeding, and promote improved patient outcomes.
