**3.7 Polymeric vs. semielemental formula**

Formulations used in EN and PN are compounds based on the following nutritional requirements: protein 1.2–1.5 g/kg/d, carbohydrates 3–6 g/kg/d (glucose concentration, aim: <10 mmol/L), lipids up to 2 g/kg/day, (triglyceride concentration, aim: <12 mmol/L), Natrium 1–2 mmol/kg/d, potassium 1–2 mmol/kg/d, chlorine 2–4 mmol/kg/d, phosphorus 0.1–0.5 mmol/kg/d, magnesium 0.1–0.2 mmol/kg/d, and calcium 0.1 mmol/kg/d. Naturally, this formula could be adapted for the clinical condition of the patient, depending on the above-mentioned serum concentrations [79]. Enteral formulas are classified into elemental (monomeric), semi-elemental (oligomeric), and standard (polymeric) formulas and differ in protein and fat concentration. Elemental formulas contain amino acids, simple sugars, and very low fats; semi-elemental formulas contain peptides of various chain lengths, a simple sugar, glucose polymers or starch, and medium-chain triglycerides, and polymeric formulas contain intact proteins, complex carbohydrates, and long-chain triglycerides [84].

Nevertheless, polymeric formulas are safe and comply with the same nutrimental function as elemental and semi-elemental formulas if administered *via* nasojejunal tube in AP patients [85–87]. A meta-analysis by Petrov et al including 1070 patients found no significant difference in feeding tolerance (RR = 0.62; 95%CI: 0.10–3.97), infection (RR = 0.48; 95%CI: 0.06–3.76), and death (RR = 0.63; 95%CI: 0.04–9.86) [85–89]. It should be remembered that semi-elemental or elemental formulas are at least sevenfold as expensive as polymeric feeds [90, 77, 91].
