Intestinal fluid absorption during exercise: role of sport drink osmolality and [Na+]

The purpose of this study was to evaluate the effects of modifying the osmo lality and [Nat] of orally ingested rehydration beverages during exercise o n intestinal absorption in the duodenum and upper jejunum. Six subjects ran domly ingested (23 mL.kg(-1) BW) the following 6% carbohydrate solutions wi th and without Nai during 85-min of cycle exercise (65% (V)over dotO(2) pea k) in a cool (22 degreesC, 40% RH) environment: a) 0 Na+, 245 mOs.mkg(-1); b) 20 mEq Na+, 283 mOsm.kg(-1);c) 20 mEq Na+, 169 mOsm.kg(-1); d) 50 mEq Na +, 275 mOsm.kg(-1); and e) 50 mEq Na+, 176 mOsm.kg(-1). To alter solution o smolality and maintain carbohydrate concentration constant, glucose, sucros e, fructose: and maltodextrin were used in different combinations. Nasogast ric and multilumen tubes were fluoroscopically placed in the stomach and in testine, respectively, to simultaneously determine gastric emptying and int estinal absorption as previously described (Lambert et al., Int. J. Sports Med. 17:48, 1996). Gastric emptying was not different among solutions and a veraged 13 +/- 0.5 mL.min(-1). Net fluid absorption was not different among beverages nor between duodenum and jejunum (x = 10.8 +/- 1.6 and 7.9 +/- 1 .1 mL.cm(-1).h(-1), respectively). Mean osmolality increased significantly (P < 0.05) from the duodenum to the jejunum (242 <plus/minus> 6 and 293 +/- 7 mOsm.kg(-1), respectively) but did not differ among solutions. These dat a provide evidence that a hypotonic 6% carbohydrate beverage with 50 mEq.L- 1 Na+ did not enhance intestinal fluid absorption or attenuate the decline in plasma volume during exercise more than an isotonic carbohydrate-electro lyte solution or a hypotonic carbohydrate solution without sodium.