Effects of isomaltulose ingestion on postexercise hydration state and heat loss responses in young men.

Isomaltulose is a disaccharide carbohydrate widely used during exercise to maintain glycaemia and hydration. We investigated the effects of ingesting a beverage containing isomaltulose and electrolytes on postexercise hydration state and physiological heat loss responses. In a randomized, single-blind cross-over design, 10 young healthy men were hypohydrated by performing up to three 30 min successive moderate-intensity (50% heart rate reserve) bouts of cycling, each separated by 10 min, while wearing a water-perfusion suit heated to 45°C. The protocol continued until a 2% reduction in body mass was achieved. Thereafter, participants performed a final 15 min moderate-intensity exercise bout followed by a 2 h recovery. Following cessation of exercise, participants ingested a beverage consisting of (i) water only (Water), (ii) 2% isomaltulose (CHO-2%), or (iii) 6.5% isomaltulose (CHO-6.5%) equal to the volume of 2% body mass loss within the first 30 min of the recovery. Changes in plasma volume (ΔPV) after fluid ingestion were greater for CHO-6.5% compared with CHO-2% (120 min postexercise) and Water (90 and 120 min) (all P ≤ 0.040). Plasma osmolality remained elevated with CHO-6.5% compared with consumption of the other beverages at 30 and 90 min postexercise (all P ≤ 0.050). Urine output tended to be reduced with CHO-6.5% compared to other fluid conditions (main effect, P = 0.069). Rectal and mean skin temperatures, chest sweat rate and cutaneous perfusion did not differ between conditions (all P > 0.05). In conclusion, compared with CHO-2% and Water, consuming a beverage consisting of CHO-6.5% and electrolytes during recovery under heat stress enhances PV recovery without modulating physiological heat loss responses.