Unpublished Letter to Triathlete Magazine

The advice in the July issue of Triathlete assumes that all fluid lost needs replacement.  The article ignores the fact that water is a byproduct of glycolysis, as has been pointed out by Tim Noakes, MD.[1]  Effectively two molecules of H2O for every molecule of glucose in glycolysis and an additional two molecules via the citric acid cycle.[2]  In the small samples cited in the magazine article one wouldn’t expect much statistical significance, but they were correct that individuals must determine their own needs.   Polymorphisms of genes such as GH1 have been shown to be associated with different sweat rates.[3]

While dipsogenic genes modulate hydration status including fluid intake, the practical conclusion from prospective and retrospective evidence is to consume fluids and electrolytes ad libitum.[1,4]

1. Noakes MD, Tim.  Lore of Running.  Champaign, IL:  Human Kinetics, 2003.
2.  Nelson, David L. and Cox, Michael M.  Principles of Biochemisty.  Worth Publishers, 2003.
3.  Walpole B, Noakes, TD, Collins M.  Growth Hormone 1 (GH1) gene and performance and post-race rectal temperature during the South African Ironman triathlon.  Br J Sports Med 2006;40:145-150.
4.  Saunders CJ, di Milander L, Hew Butler T, Xenophontos SL, Carioulou MA, Anastassiades LC, et al.  Dipsogenic genes associated with weight changes during Ironman Triathlons.  Human Mol Genet.  2006 Oct 15;15(20):2980-7. Epub 2006 Sep 1.

In hindsight the above could have been more refined; but, the bottom line is chemical equations need to be balanced.  One can expect fluid lost in sweat is partly a byproduct of glycolysis.  Enough with the dangerous medical advice.