SHI, X., R. W. SUMMERS, H. P. SCHEDL, S. W. FLANAGAN, R-T. CHANG, and C. V. GISOLFI. Effects of carbohydrate type and concentration and solution osmolality on water absorption.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1607–1615, 1995. We studied intestinal absorption of solutions containing either one (glucose, Glu, or maltodextrin, Mal) or two (fructose, Fru, and Glu or sucrose, Suc) transportable carbohydrate (CHO) substrates using segmental perfusion technique in eight healthy male subjects. These CHO were either free and directly transportable monosaccharides (Glu, Fru), bound as the disaccharide (sucrose, Suc), or as oligomers (maltodextrins, Mal). [CHO] was varied from 6% to 8% (120–444 mmol·l-1). All solutions contained low [Na+] (15–19 mEq) and [K+]_(3–4 mEq). Solutions osmolalities varied from 165 to 477 mOsm·kg-1. Osmolalities in the test segment ranged from 268 to 314 mOsm·kg-1. The regression line of osmolality with water absorption differed for single as compared with multiple substrate solutions. The significantly different intercepts of these two regression lines suggest that solutions with multiple substrates produce greater water absorption at a given osmolality than those with one. Comparing all solutions, test segment solute flux (partial r = 0.69) was more important than mean osmolality (partial r = 0.32). In conclusion, solutions with multiple substrates stimulate several different solute absorption mechanisms yielding greater water absorption than solutions with only one substrate.