Effect of glucose solutions on fluid availability at rest and exercise in humans
This thesis examined relationships between the composition of ingested solutions and nutrient availability in humans. The rate of fluid and energy availability from an ingested solution depends upon both gastric emptying (GE) and intestinal absorption processes. Experimental results demonstrated that the GE rate of fluid in resting man was significantly delayed by ingestion of ≥6.4 carbohydrate (CHO) solutions, but not by a dilute 2% CHO solution. Conversely, the rate of energy delivery to the intestine was highest for ≥6.4% CHO solutions. Solution osmolality had no influence on the GE rate of a 6.4% CHO solution. Relative field uptake rates for 0, 2 and 6.4% CHO solutions were also examined using a 2H technique in resting humans. Although fluid uptake rates were statistically similar for these solutions, the results suggested a trend for the 2% CHO solution to promote the highest rate of fluid uptake. Lastly, the effect of glucose concentration on cycling capacity under temperate conditions was examined. Endurance-trained subjects ingested 0 (i.e. water), 2, 4 or 6% glucose solutions during separate 90 min cycles at ~70% VO2 peak, before cycling to exhaustion at 95% VO2 peak. In comparison with the 0% glucose solution, cycling capacity was significantly improved by the 4% glucose solution only. There was no clear explanation for this result, but it was suggested that improved fluid availability and central function may be partly responsible.