ObjectiveTo investigate the protein intake of patients in the general surgery intensive care unit (ICU) and to analyze the factors, both hindering and facilitating, that affecting protein intake from the perspective of healthcare professionals. MethodsA mixed-methods approach was used in this study, including a quantitative study and a qualitative study. A quantitative study assessed the protein intake in ICU patients. A qualitative study analyzed the perspectives of healthcare professionals via semi-structured interviews. In the quantitative study, 32 variables were analyzed, and the sample size was estimated to be 10 times the number of study variables. The qualitative study employed the maximum difference sampling strategy, with the sample size determined by data saturation. Multiple linear regression was used to identify risk factors affecting protein intake achievement, with a significance level of α=0.05. ResultsThe quantitative study included 459 patients, with a protein intake of (0.739±0.552) g/(kg·d). Of the patients, 90 (19.6%) had a protein intake of 1.2–2.0 g/(kg·d), 11 (2.3%) had ≥2.0 g/(kg·d), and 358 (78.0%) had <1.2 g/(kg·d). The multiple linear regression analysis identified several risk factors influencing protein intake attainment, including male sex, higher body mass index, elevated blood glucose levels upon ICU admission, late initiation of enteral nutrition (>48 h), nasoenteric tube placement, and the use of enteral nutrition feedings. In the qualitative study, three key themes were identified from the interviews: inadequate infrastructure, healthcare workers’ factors, and patient-related factors. ConclusionThe findings of this study suggest a substantial gap between the protein intake of general surgical ICU patients and the guideline-recommended intake. The study highlights patient groups at risk for inadequate protein intake based on identified risk factors. Future efforts should focus on improving the efficiency of protein supplementation, enhancing the nutritional status of patients, standardizing protein supplementation protocols, and increasing education for both healthcare workers and patients.