The critically ill patient undergoes an obligatory hypercatabolic phase and is at risk to an increasing nutrional deficit during the ICU length of stay. Exclusive enteral nutrition (EN)results in underfeeding proven to be associated with higher morbidity and mortality in the critically ill. Adequate energy and protein targets often cannot be obtained before 1 week with EN alone. We have hypothesized that supplemental parenteral nutrition (SPN) combined with EN would be an effective alternative to achieve the 100% energy target from day 4, when EN support was less than 60% by day 3. The results of such a combined nutrition support are recently published in the Swiss “SPN study” and showed clinical outcome benefits in critically ill patients with less nosocomial infections by achieving 100 % energy goals from admission day 4 to day 8. The constantly changing energy requirements during critical illness should be most accurately adapted by indirect calorimeter measurements. Indeed close nutritional and metabolic monitoring together with consequent adjustments of nutritional support improves clinical outcome of critically ill patients. In contrary, inadequate parenteral feeding in ICU patients without real indication worsens clinical outcome. With a combined nutrition support concept not only the best energy requirements but also optimized protein targets can be promoted. Whether the determination of the best protein target for the critically ill and protein support adaptation during the acute and post-acute phase of critical illness provides additional overall outcome benefits has to be ascertained in further studies. Further research should focus more on studies of more personalized nutritional management and early physical rehabilitation programs according to the individual specific needs of the ICU patient.