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Lawrence E. Armstrong

Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. In the 10 studies reviewed, consumption of a CB resulted in 0-84% retention of the initial volume ingested, whereas consumption of water resulted in 0-81% retention. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes and recreational enthusiasts will not incur detrimental fluid-electrolyte imbalances if they consume CB in moderation and eat a typical U.S. diet. Sedentary members of the general public should be at less risk than athletes because their fluid losses via sweating are smaller.

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Philo U. Saunders, Laura A. Garvican-Lewis, Robert F. Chapman, and Julien D. Périard

practices should counterbalance the increased fluid loss via ventilation and diuresis, although consumption of large volumes in the evening should be avoided to reduce night waking to pass urine. Macronutrient requirements and overall caloric intake need to be increased at altitude due to a likely increased

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Alan J. McCubbin, Bethanie A. Allanson, Joanne N. Caldwell Odgers, Michelle M. Cort, Ricardo J.S. Costa, Gregory R. Cox, Siobhan T. Crawshay, Ben Desbrow, Eliza G. Freney, Stephanie K. Gaskell, David Hughes, Chris Irwin, Ollie Jay, Benita J. Lalor, Megan L.R. Ross, Gregory Shaw, Julien D. Périard, and Louise M. Burke

alone, via increased ad libitum fluid intake subsequent to increased osmotic thirst drive ( Hoffman et al., 2019 ), reduced diuresis, and/or movement of fluid from the intracellular to extracellular space ( Sanders et al., 2001 ). However, the influence on [Na + ] plasma is minor ( Hew-Butler et

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Louise M. Burke, John A. Hawley, Asker Jeukendrup, James P. Morton, Trent Stellingwerff, and Ronald J. Maughan

–80% fat. • Popular K-LCHF book ( Volek & Phinney, 2012 ) recommends electrolyte supplementation to combat sodium diuresis associated with this diet. • Adaptations achieve extremely high rates of fat oxidation during exercise (up to 1.8–2 g/min; Burke et al., 2017a ; Volek et al., 2015 ). • While