Proabsorptive effect of glycerol as a glucose substitute in oral rehydration solutions

Effects of ingesting beverages containing glycerol and sodium with isomaltulose or sucrose on fluid retention in young adults: a single-blind, randomized crossover trial

We evaluated changes in hyperhydration and beverage hydration index (BHI, a composite measure of fluid balance after consuming a test beverage relative to water) during resting, induced by the consumption of beverages containing glycerol and sodium supplemented with fast-absorbing sucrose or slow-absorbing isomaltulose. In a randomized crossover, single-blinded protocol (clinical trials registry: UMIN000042644), 14 young physically active adults (three women) consumed 1 L of beverage containing either 7% glycerol + 0.5% sodium (Gly + Na), Gly + Na plus 7% sucrose (Gly + Na + Suc), Gly + Na plus 7% isomaltulose (Gly + Na + Iso), or water (CON) over a 40 min period. We assessed the change in plasma volume (ΔPV), BHI (calculated from cumulative urine output following consumption of water relative to that of the beverage), and blood glucose and sodium for 180 min after initiating ingestion. Total urine volume was reduced in all beverages containing glycerol and sodium compared to CON (all P ≤ 0.002). The addition of isomaltulose increased BHI by ∼45% (3.43 ± 1.0 vs. 2.50 ± 0.7 for Gly + Na, P = 0.011) whereas sucrose did not (2.6 ± 0.6, P = 0.826). The PV expansion was earliest for Gly + Na (30 min), slower for Gly + Na + Suc (90 min), and slowest for Gly + Na + Iso (120 min) with a concomitant lag in the increase of blood glucose and sodium concentrations. Supplementation of beverages containing glycerol and sodium with isomaltulose but not sucrose enhances BHI from those of glycerol and sodium only under a resting state, likely due to the slow absorption of isomaltulose-derived monosaccharides (i.e., glucose and fructose).