Aims: Major trauma patients need adequate nutrition for recovery. This study aimed to evaluate the adequacy of nutritional supply and the correlation between nutritional supply and clinical outcome. Methods: A single-centre retrospective observational study was undertaken, describing the amounts of energy and proteins provided to 320 critically ill trauma patients during the first 10 days after admission. The data were collected from the electronic medical records of patients admitted to the trauma intensive care unit during the study period and descriptive statistical analyses were performed with the SPSS software. Results: The mean proportion of supplied energy to recommended energy during the first 10 days after admission was 57.5%, and the mean percentage of supplied protein to recommended protein intake was 51.3%. The patients were divided into those who received ≥70% (isocaloric nutrition group) and those who received <70% (hypocaloric nutrition group) of their estimated requirements. Both the duration of ventilator use (12.7 ± 10.5 vs. 16.0 ± 15.8 days, respectively, p = 0.009) and duration of parenteral nutrition (1.1 ± 1.4 vs. 2.0 ± 2.0 days, respectively, p = 0.001) were shorter in the isocaloric nutrition group (n = 83) than in the hypocaloric nutrition group (n = 237). Conclusion: Total energy and the amount of protein supplied were insufficient compared to the recommended amount. The duration of ventilator use was shorter in the isocaloric nutrition group than in the hypocaloric nutrition group. The association between shortened ventilator use and isocaloric nutrition requires further investigation as a potential intervention to reduce the risk of complications such as ventilator-related pneumonia.