Clear study hypothesis / research question It has already been proven that a prolonged negative energy balance during intensive care stay is an independent risk factor for mortality. Although it was thought that achivieng optimal delivery of calories will prevent nutritional deficits in critically ill patients, published randomized controlled trials failed to confirm this hypothesis. Combinging enteral and parenteral support may be an efficent strategy to reach nutritional target in critically ill patients. According to the current guidelines the use of suplemental parenteral nutrition (SPN) should be considered when energy targets are not achieved by enteral (EN) route, however, no clear data regarding timing, amount and composition is specified. Moreover, based on recente published data overfeeding should also be avoided, considering the negative impact on outcome. Nutritional support for critically ill patients was focused more on preventing caloric and protein deficits and no great emphasis was placed on the efficiency of intestinal absorption. Gastrointestinal dysfunction is a prevalent reported complication that may contribute to falling short of meeting nutritional goals. This encompasses a wide spectrum of symptoms, such as impaired gastric emptying, ileus or impaired intestinal absorbtion, exposing patients to feeding intolerance, malnutrition and worse outcomes. No standard definition and monitoring techniques are so far available for the diagnostic of feeding intolerance. Although increased gastric residual volume (GRV) is the most used parameter for highlighting feeding intolerance, a controversy regarding the adequate threshold of GRV persists. Acetaminophen absorption test has been previously proposed as a diagnostic tool to asses impaired gastric emptying and intestinal absorbtion. Besides intestinal absorbtion, efficient utilization of macronutients should also be assessed, considering that critically ill patients have varying metabolic conditions and may not be able to metabolically handle adminsitered substrates. As a result body composition analysis should be taken into account in order to obtain a dynamic quantification, especially, of the mucle mass compartiments. Therefore the following low-interventional study is designed to investigate the hypothesis regarding energy and protein intake achievement in critically ill patients with diagnosed impaired gastrointestinal dysfunction to whom tailored nutritional support is administered. Taking into account that we aim to identify patients with early-phase gastrointestinal dysfunction impaired gastric emptying and reduced intestinal absorbtion (diagnosed using ultrasound gastric residual volume and byacetaminiphen absorbtion test) will serve as defining factors. Patients will be randomized to receive nutritional support either according to the EN protocol or enteral trophic feed + SPN protocol. Differences in rectus femoris thickness measured on admission, on day 10 and 15, variation of lean body mass measured by bioelectrical impedance on admission on day 10 and 15, and differences between groups in muscle function using handgrip dynamometer will also be evaluated in both groups.