The role of osmolality in the absorption of a nutrient solution

Background: Loss of water during enteral nutrition following massive intestinal resection may be severe. Low osmolality of oral rehydration solutions has recently been shown to mediate an increase in water absorption. Aim: To evaluate the effect of osmolality of a nutrient solution on the intraluminal duodenojejunal water flow, and the net absorption rates of total nitrogen and carbohydrate. Methods: Eight healthy volunteers with a mean age of 27 (range 25–29) years participated in the study. Enteral nutrition (17% protein, 59% carbohydrate, 24% lipid plus 5 g/L PEG 4000) was infused (5 mL/min 2.64 kcal/min) into the descending duodenum either as a hypotonic (160 mOsmol/kg) or as an isotonic solution in a random order. Intestinal samples were aspirated 20 and 45 cm distally to the infusion point. Results: Intraluminal water flow rates were significantly lower with the hypotonic solution than with the isotonic solution, both in the duodenum (4.9 ± 0.3 vs. 6.7 ± 0.5 mL/min; P < 0.02) and the upper jejunum (3.0 ± 0.1 vs. 3.9 ± 0.2 mL/min; P < 0.005). The net absorption rates of total nitrogen and carbohydrate were similar with both solutions. Conclusion: Low osmolality of a nutrient solution decreases intraluminal water flow rates in the upper intestine without affecting the absorption rates of total nitrogen and carbohydrate. Compared with an isotonic solution, the use of a hypotonic solution might lower the water loss in patients with extensive short bowel intestinal resection.