Nutrition therapy provided early in the critical care setting has been shown to improve outcome. Appropriate and early nutrition interventions can attenuate the hyperdynamic systemic response and depressed immune reaction to injury, serious illness and major surgery. Controversies limit the uniform application and potential benefits of nutrition, including failure to accurately predict who will 'need' nutritional intervention, lack of consensus on what the optimal enteral formulation is, overreliance on parenteral nutrition, failure to maximize the use of early enteral nutrition (EN), and how much and how best to feed the morbidly obese population. Despite challenges and inconsistencies in today's critical care setting, specialized nutrition has evolved from metabolic 'support' during critical illness to a primary therapeutic intervention designed, individualized and focused to achieve metabolic optimization and mitigation of stress-induced immune and hyperdynamic systemic responses. Nutrition should be considered early and commenced after initial resuscitation has taken place. This is most effectively accomplished with the use of protocols that aggressively promote early EN, and will result in lower mortality and a reduction in major complications. Though the complexity of the heterogeneous critically ill population will always be challenging, we are developing a better understanding of immunity, metabolic needs and catabolism associated with intensive care unit admissions.