The goal of this clinical trial is to determine the optimal protein administration strategy for enhancing both nutritional and clinical outcomes, as well as reducing complications and mortality in ICU patients at risk for refeeding syndrome (RS). This study will include critically ill patients at risk for RS who are receiving supportive nutrition. The primary hypothesis is that higher protein intake will lead to a decreased incidence of refeeding syndrome. It is also expected that patients receiving more protein will have better clinical outcomes, lower mortality, and shorter ICU and hospital stays.

Patients will be randomly assigned to two groups: the high-protein group and the standard-protein group. Upon ICU admission, and after meeting the inclusion criteria and identifying a risk of refeeding syndrome (RS), they will be allocated to one of the two groups. Patient selection for RS risk will be based on the diagnostic criteria outlined in the 2020 ASPEN guidelines. The m-NUTRIC and APACHE II scores will be calculated for all patients at ICU admission and 24 hours before the initiation of feeding. Monitoring for multi-organ dysfunction syndrome (MODS) will involve daily laboratory tests and organ failure assessment using the SOFA score.

Before starting the nutritional intervention, all patients will receive 100 mg of thiamine daily for one week, along with a daily multivitamin-mineral supplement. Due to the risk of RS, calorie intake will begin at low levels and will be cautiously increased in both groups. To calculate the energy needs, ideal body weight will be used. In the high-protein group, the target protein intake will be 2 grams per kilogram of body weight per day, while in the standard-protein group, it will be 1.3 grams per kilogram of body weight per day. Protein will be introduced gradually, starting from a low level, as part of nutritional support, with whey protein powder added if needed as a supplement. If serum creatinine levels rise, protein powder will be removed from the patient's diet. The intervention duration will be 14 days, with a minimum of 5 days.

The primary clinical outcome is the incidence of refeeding syndrome (RS), while secondary outcomes include the occurrence of infections, hospital length of stay, ICU length of stay, multi-organ failure, and mortality within 45 days of admission. RS will be diagnosed according to the 2020 ASPEN guidelines. Serum concentrations of potassium, magnesium, phosphate, glucose, urea, and creatinine will be measured daily for one week.

Inclusion Criteria:

• Willingness to cooperate and complete the informed consent form by the patient or legal guardian;
• age ≤ 18 years and < 65 years;
• Non-pregnant and non-lactating;
• Serum creatinine ≥ 1.1 mg/dl for women and ≥ 1.2 mg/dl for men;
• No organ failure at the time of study enrollment;
• Intervention initiation within 48 hours of ICU admission;
• No history of metastatic cancer or end-stage disease;
• No absolute contraindications to enteral nutrition (e.g., persistent ileus, gastrointestinal ischemia, persistent or biliary vomiting, mechanical obstruction);
• No active infections, sepsis, severe sepsis, or septic shock;
• No intolerance to the whey protein supplement used in the current study;
• Not participating in other clinical trials concurrently with this study;
• No clinical conditions with higher or lower protein needs, such as burns, sepsis, cirrhosis, or chronic kidney disease;
• No diabetes with severe complications such as ketoacidosis, hyperosmolar coma, or acidosis.

Exclusion Criteria:

• Unwillingness to continue cooperation during study;
• Discharge or death of the patient earlier than 5 days from the start of the intervention;
• Occurrence of side effects during the study