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Article

The Sodium Concentration of Enteral Diets Does Not Influence Absorption of Nutrients but Induces Intestinal Secretion of Water in Miniature Pigs

Institute of Physiology, University of Hohenheim, Stuttgart, Germany

Contradictory opinions exist as to whether the sodium concentration of enteral diets influences absorption of macronutrients and transepithelial movement of sodium and water. Therefore, we investigated the effects of various sodium concentrations of enteral diets on absorption of macronutrients and on net fluxes of sodium and water. In unanesthetized miniature pigs, a 150-cm jejunal segment was perfused with an oligopeptide (Peptisorb), an oligomeric and a polymeric diet. The polymeric diet was supplemented with pancreatic enzymes. The sodium concentrations varied between 30 and 150 mmol/L. The energy density was 3.4 MJ/L. The sodium concentration of the diets did not influence absorption of macronutrients and of total energy. However, increasing sodium concentrations of the diets were associated with increasing osmolality of the solutions, resulting in a linear increase in net secretion of water and flow rate of chyme. With all diets and sodium concentrations net secretion of sodium occurred. The sodium secretion was independent of the initial sodium concentration of the diets. It was linearly correlated with net flux of water and was largest in miniature pigs infused with the oligomeric diet. The sodium concentration of the jejunal effluent did not correspond to the initial sodium concentration of the diets. The present results indicate that enteral feeding of diets with high energy density inevitably increases net secretion of water and sodium as sodium concentration increases. Therefore, the sodium concentration of diets should be as low as possible to meet only the minimal daily requirement of sodium. Low sodium concentrations of diets have no negative effects on absorption of macronutrients.

KEY WORDS: • enteral nutrition • sodium • osmolality • miniature pigs • water secretion