Bottle mixology
Your sports drink works by osmosis: too concentrated, and it pulls water out of your blood instead of putting it back. We paid so you would know. Enter your recipe and the tool tells you whether it is fuel or an enema.
The science behind the tool
Osmolarity
What counts is the number of dissolved particles, not their mass. Your plasma runs at ~290 mOsm/L. Below that, the water in your bottle moves into the blood. Above it, your gut has to dilute first, using water from your plasma. You dehydrate yourself by drinking.
Maltodextrin
One maltodextrin molecule (~1800 g/mol) carries the energy of 10 glucose units for the osmotic pressure of a single particle. That is the hack that lets you put 60 g of carbs in a bottle that stays hypotonic.
The SGLT1/GLUT5 duo
Glucose goes through SGLT1 (~60 g/h max), fructose through GLUT5 (~30 g/h on top). To pass 60 g/h without blowing up your gut you need both. Hence the 2:1 and 1:0.8 ratios of the serious products (and of our presets).
Sodium
Its real job during exercise: keeping the water you drink. Plain water dilutes your blood, the kidney switches off the water-holding hormone and part of your bottle ends up in the toilet. Salted, the same drink stays in. As for driving SGLT1, the gut does that with its own sodium.
Potassium
Sweat takes out ten times less of it than sodium, and your body stores ~140 g. The link with cramps is not proven. We add little, at the level of commercial drinks: insurance for when your bottles switch to plain water, nothing more.
Hyponatraemia
Blood sodium crashing during long events. First cause: drinking more than you sweat, not a lack of salt. Even a well salted bottle is more dilute than your blood. The fix is drinking to thirst; salt slows the drop, it does not stop it.
Sources
Jentjens RL, Moseley L, Waring RH, Harding LK, Jeukendrup AE (2004). Oxidation of combined ingestion of glucose and fructose during exercise. J Appl Physiol · 96(4):1277-1284 · glucose + fructose oxidised beyond the glucose-only ceiling · 10.1152/japplphysiol.00974.2003
Jeukendrup AE (2010). Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Curr Opin Clin Nutr Metab Care · 13(4):452-457 · SGLT1 saturates around 60 g/h, GLUT5 adds its own route: where 90 g/h comes from · 10.1097/MCO.0b013e328339de9f
Rowlands DS, Houltham S, Musa-Veloso K, Brown F, Paulionis L, Bailey D (2015). Fructose–glucose composite carbohydrates and endurance performance: critical review and future perspectives. Sports Med · 45(11):1561-1576 · critical review of glucose-fructose blends and ratios · 10.1007/s40279-015-0381-0
Podlogar T, Wallis GA (2022). New horizons in carbohydrate research and application for endurance athletes. Sports Med · 52(Suppl 1):5-23 · the 1:0.8 ratio and intakes beyond 90 g/h · 10.1007/s40279-022-01757-1
Gisolfi CV, Summers RW, Schedl HP, Bleiler TL (1995). Effect of sodium concentration in a carbohydrate-electrolyte solution on intestinal absorption. Med Sci Sports Exerc · 27(10):1414-1420 · drink sodium barely changes glucose absorption: the gut supplies SGLT1 with its own · 10.1249/00005768-199510000-00010
Sutehall S, Muniz-Pardos B, Bosch AN, Di Gianfrancesco A, Pitsiladis YP (2018). Sports drinks on the edge of a new era. Curr Sports Med Rep · 17(4):112-116 · alginate and pectin hydrogel drinks · 10.1249/JSR.0000000000000475
Maughan RJ, Leiper JB (1995). Sodium intake and post-exercise rehydration in man. Eur J Appl Physiol · 71(4):311-319 · the saltier the drink, the less of it you urinate away · 10.1007/BF00240410
Shirreffs SM, Maughan RJ (1998). Volume repletion after exercise-induced volume depletion in humans: replacement of water and sodium losses. Am J Physiol Renal Physiol · 274(5):F868-F875 · volume and sodium together to hold on to the water · 10.1152/ajprenal.1998.274.5.F868
Maughan RJ, Watson P, Cordery PA, Walsh NP, Oliver SJ, Dolci A, et al. (2016). A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. Am J Clin Nutr · 103(3):717-723 · the beverage hydration index: salted rehydration solution retained better than water · 10.3945/ajcn.115.114769
Baker LB (2017). Sweating rate and sweat sodium concentration in athletes: a review of methodology and intra/interindividual variability. Sports Med · 47(Suppl 1):111-128 · sweat sodium varies several-fold from one athlete to the next · 10.1007/s40279-017-0691-5
Baker LB (2019). Physiology of sweat gland function: the roles of sweating and sweat composition in human health. Temperature · 6(3):211-259 · sweat composition, potassium included, small next to sodium · 10.1080/23328940.2019.1632145
Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS (2007). American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc · 39(2):377-390 · ACSM position stand: drinking, sodium, exercise duration · 10.1249/mss.0b013e31802ca597
Hew-Butler T, Rosner MH, Fowkes-Godek S, Dugas JP, Hoffman MD, Lewis DP, et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clin J Sport Med · 25(4):303-320 · consensus: exercise hyponatraemia comes first from drinking more than you lose · 10.1097/JSM.0000000000000221
Hoffman MD, Stuempfle KJ (2015). Sodium supplementation and exercise-associated hyponatremia during prolonged exercise. Med Sci Sports Exerc · 47(9):1781-1787 · in ultras, salt alone does not prevent hyponatraemia if you overdrink · 10.1249/MSS.0000000000000599
Schwellnus MP (2009). Cause of exercise associated muscle cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion? Br J Sports Med · 43(6):401-408 · the cramp / electrolyte link is weak, the neuromuscular explanation dominates · 10.1136/bjsm.2008.050401
EFSA NDA Panel (2016). Dietary reference values for potassium. EFSA Journal · 14(10):e04592 · 3.5 g of potassium a day for adults: the plate, not the bottle · 10.2903/j.efsa.2016.4592