This is a research study to determine if a particular method of providing nutrition improves the clinical outcomes of patients in the intensive care unit (ICU) who have undergone abdominal surgery and would require nutrition delivered via the bloodstream (called total parenteral nutrition or TPN). The nutrition method we are testing is a structured nutrition delivery plan that involves tube feeding, oral nutrition supplements, and the use of a device (called an indirect calorimeter or IC) to measure calorie needs. This study will also use two devices to measure fat and muscle mass to examine changes during hospitalization. Subjects will be followed throughout hospitalization where nutrition status and fat and muscle mass will be closely monitored. Study activities will begin within 72 hours of a patient's abdominal surgery. TPN (total parenteral nutrition, a method of feeding that bypasses the usual process of eating and digestion) will be started, a non-invasive method of assessing calorie needs (indirect calorimetry (IC)) will be started, a urine sample will be collected to help assist in protein needs, and fat/muscle mass will be measured using bioelectrical impedance analysis (BIA), and an ultrasound. This is a minimal risk study and all products/devices used are non-invasive and FDA-approved. Indirect calorimetry and urine sample collection will be conducted every 3 days during the stay in the Intensive Care Unit - ICU, then every 5 days until hospital discharge. BIA and muscle ultrasound will be conducted every 7 days during ICU stay, then every 14 days until hospital discharge.