Background: Finding the best energy and protein dose and timing for critically ill patients remains challenging. Distinct populations may react differently to protein load. This study aimed to characterize and predict outcomes of critically ill patients who received moderate energy and high or low protein doses during their stay in the intensive care unit (ICU). Methods: The cohort included 646 adult patients (70% men and 30% women) hospitalized in Beilinson Hospital ICU (Petah Tikva, Israel) for over 5 days between 2011 and 2018. Patients received 10–20 kcal/kg/day and were classified into two groups: low (LP) and high (HP) protein support (≤1 g/kg/day vs. >1 g/kg/day), the LP group comprising 531 patients (82%) and the HP group 115 patients (18%). Multiple logistic regression was used to describe associations between patients’ characteristics and 90-day survival in the LP and HP groups. Results: Among LP, increased age, APACHE II, and receiving supplemental parenteral nutrition (SPN) were associated with decreased survival (OR = 0.986, 95% CI [0.973, 0.999]; OR = 0.915, 95% CI [0.886, 0.944], OR = 0.579, 95% CI [0.366, 0.917]). Trauma admission was associated with increased survival (OR = 1.826, 95% CI [1.001, 3.329]). Among HP, increased age was associated with decreased survival (OR = 0.956, 95% CI [0.924, 0.998]). Higher BMI was associated with improved survival (OR = 1.137, 95% CI [1.028, 1.258]). Likewise, in the HP group, the BMI of elderly survivors was higher compared to non-survivors (27.1 ± 6.2 vs. 24.7 ± 4.8, t (113) = 2.3, p < 0.05). Conclusions: Our results show that in patients with moderate energy support and low protein administration, survivors were younger, with a lower APACHE II score, mainly suffering from trauma and without renal failure. In the patients receiving high protein support, younger patients with a high BMI not suffering from sepsis were more likely to survive. We suggest confirming these findings with prospective RCTs.
