Year: 2012
Type: dissertation
Abstract: It is known that during fluid restriction, obligatory water losses continue and\nhypohydration develops and that restricted energy intake leads to a concomitant\nrestriction of all other dietary components, as well as hypohydration, but the specific\neffects of periods of fluid and/ or energy restriction on fluid balance, electrolyte\nbalance and exercise performance have not been systematically described in the\nscientific literature.\nThere were two main aims of this thesis. Firstly, to describe the effects of periods of\nsevere fluid and/ or energy restriction on fluid and electrolyte balance; secondly, to\ndetermine the effect of electrolyte supplementation during and after energy restriction\non fluid and electrolyte balance as well as energy exercise performance.\nThe severe restriction of fluid and/ or energy intake over a 24 h period all resulted in\nbody mass loss (BML) and hypohydration, but whilst serum osmolality increases\nduring fluid restriction (hypertonic hypohydration), serum osmolality does not change\nduring energy restriction (isotonic hypohydration), despite similar reductions in\nplasma volume (Chapter 3). These differences in the tonicity of the hypohydration\ndeveloped are most likely explainable by differences in electrolyte balance, with fluid\nrestriction resulting in no change in electrolyte balance over 24 h (Chapter 3) and\nenergy restriction (with or without fluid restriction) producing significant reductions\nin electrolyte balance by 24 h (Chapter 3; Chapter 4; Chapter 5; Chapter 6; Chapter\n7).\nTwenty four hour combined fluid and energy restriction results in large negative\nbalances of both sodium and potassium, and whilst the addition of sodium chloride to\na rehydration solution ingested after fluid and energy restriction increases drink\nretention, the addition of potassium chloride to a rehydration solution does not\n(Chapter 4).\nSupplementation of sodium chloride and potassium chloride during periods of severe\nenergy restriction reduces the BML observed during energy restriction and maintains\nplasma volume at pre-energy restriction levels (Chapter 5; Chapter 6; Chapter 7).\niv\nThese responses to electrolyte supplementation during energy restriction appear to be\nrelated to better maintenance of serum osmolality and electrolyte concentrations and a\nconsequential reduction in urine output (Chapter 5; Chapter 6; Chapter 7).\nAdditionally, 48 h energy restriction resulted in a reduction in exercise capacity in a\nhot environment and an increase in heart rate and core temperature during exercise,\ncompared to a control trial providing adequate energy intake. Whilst electrolyte\nsupplementation during the same 48 h period of energy restriction prevented these\nincreases in heart rate and core temperature and exercise capacity was not different\nfrom the control trial Chapter 8).\nIn conclusion, 24-48 h energy restriction results in large losses of sodium, potassium\nand chloride in urine and a large reduction in body mass and plasma volume and\nsupplementation of these electrolytes during energy restriction reduces urine output,\nattenuates the reduction in body mass and maintains plasma volume and exercise\ncapacity.
Author: Lewis J. James
Language: English
Subfield: Physiology (medical)
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W815592175