Obesity compounds the metabolic response to critical illness and augments the consequences of overfeeding. Effective monitoring is essential for the prevention of, or to avoid, worsening of preexistent morbidities associated with obesity during the implementation of specialized nutrition support. This monitoring should guide the clinician toward the selection of appropriate therapeutic options to reduce complications from significant hyperglycemia, dyslipidemia, hypercapnia, fluid overload, and worsening of hepatic steatosis. Conventional nutrition outcome markers should be employed, with their limitations understood, when used for the critically ill obese patient.