The consequences of ingesting different carbohydrate solutions on fluid movement
and availability have not been systematically examined. In addition, the role of
carbohydrate in the post-exercise rehydration period has received little attention
despite the need for substrate replenishment following exercise and the role of
carbohydrates in stimulating water absorption in the intestine. The aims of this thesis
were to assess fluid absorption characteristics and availability of solutions containing
increasing concentrations of glucose and to evaluate their role in the restoration and
maintenance of fluid balance following a period of exercise-induced dehydration.
The ingestion of a single bolus of a commercially available hypertonic 18%
carbohydrate solution (chapter 3) and a hypertonic 10% glucose solution (chapter 4)
resulted in reductions in plasma volume that are most likely due to acute net secretion
of water into the intestinal lumen. When investigating recovery of whole body
hydration status after sweat loss, a hypertonic 10% glucose-electrolyte solution
maintained whole body fluid balance for a longer period than a hypotonic 2%
glucose-electrolyte solution and an electrolyte only solution when a fixed volume of
fluid was consumed during a rehydration period of one hour following cycle exercise
in the heat (chapter 5). When fluid was consumed ad libitum over a two hour period
following similar cycle exercise in the heat, a hypertonic 10% glucose-electrolyte
solution was as effective in restoring and maintaining fluid balance as a 2% hypotonic
glucose-electrolyte solution and an electrolyte only solution (chapter 6). The reduced
rate of gastric emptying that accompanies the ingestion of high carbohydrate solutions
was likely to be the primary cause for the difference in urine production reported
between thetrials during this study (chapter 7).
In conclusion, ingestion of hypertonic carbohydrate solutions results in a
reduction in extracellular fluid volume that is most likely due to secretion of water
into the intestinal lumen and the carbohydrate content of an ingested solution is of
importance in the post-exercise rehydration period.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.