The goal of this clinical trial is to systematically evaluate whether peptide-type enteral nutrition (EN) formulations improve protein uptake efficiency in high-risk groups at ICU PEI, using targeted amino acid metabolomics and gut microbiota co-metabolomics as core quantitative indicators.

Researchers will compare protein absorption efficiency of short-chain peptide and complete protein enteral nutrition formulas in high-risk populations for PEI in the ICU

Participants will:

Enteral nutrition was administered for ICU critically ill patients with high-risk factors for PEI

The study subjects that meet the inclusion criteria will be randomly assigned in a 1:1 ratio to the peptide group and the whole protein group according to the following allocation scheme:

1. Peptide Group: Receives nutritional support therapy with a peptide-based enteral nutrition (EN) formulation. The selected formulation must contain 5 g of protein per 100 ml and be composed entirely of hydrolyzed whey protein, which can be absorbed by the intestine without the need for thorough digestion by pancreatic enzymes.
2. Whole Protein Group: Receives nutritional support therapy with a whole protein-based EN formulation. The selected formulation also contains 5 g of protein per 100 ml and consists of intact protein components, which require digestion and breakdown by pancreatic enzymes before being absorbed.

Both groups of study subjects will strictly follow the 2025 ASPEN Guidelines for Nutritional Therapy in Critically Ill Patients and the relevant expert consensus on critical care nutrition in China. Apart from the difference in the type of EN formulation, all other treatment measures (including anti-infection therapy, organ function support, gastrointestinal motility regulation, sedation and analgesia) will be carried out in accordance with standard ICU clinical practices to ensure consistency in the baseline treatment conditions between the two groups.

Inclusion Criteria:

• Age≥ 18 years old, no gender restriction;
• Meet the criteria for high-risk groups for PEI;
• AGI≤ Class II, hemodynamically stable, meeting EN initiation criteria;
• Estimated duration of enteral nutrition support therapy: ≥7 days;
• The subject or their legally authorized family member must sign the informed consent form

Exclusion Criteria:

• Patients who have been clearly diagnosed with PEI or chronic persistent PEI;
• Patients who have contraindications to enteral nutrition therapy;
• Patients with severely impaired liver or kidney function;
• Patients who suffer from amino acid metabolism disorders, severe malnutrition, or cachexia;
• Patients who have received pancreatic enzyme replacement therapy or taken any medications that may affect protein absorption within 7 days prior to enrollment;
• Patients for whom the expected length of ICU stay is less than 7 days;
• Pregnant or lactating women, as well as patients with mental illnesses;
• Patients who are allergic to any component of the study medication.