Strategies for providing optimal nutritional therapy have evolved over time, with the emphasis on specific directives (such as route, use of immunonutrition, high protein, organ-specific formulas, etc.), achieving variable degrees of success for improving outcomes in the intensive care unit. As the largest immune organ in the body comprising the largest interface between the host and the external environment, the gut can have an amplifying effect on a pattern of dysbiosis, immune dysregulation, and multiple organ failure seen in the critically ill patient. Conversely, maintenance of gut integrity can serve to restore a pattern of homeostasis, appropriate immune responses, symbiosis, and clinical recovery. Simply providing refined polymeric formulas as enteral nutrition may not take full advantage of the potential for optimal outcome that could be derived by giving therapy designed to directly stimulate gut defenses and support the intestinal microbiota. This article describes a series of strategies (such as use of intact whole food formulas, soluble fiber, fecal microbial transplantation, serum bovine immunoglobulin, or agents to promote commensal behavior) that should modulate the gut microbiome and shift the critically ill patient toward a pattern of health and recovery.