Looking for a little science to back this up. If I mix in 60g of carbs into a 1 litre bottle does that diminish the hydrating effects of the drink? I’ve read that Isotonic (6-8%) don’t hydrate. Which kind of surprised me.
Are you adding additional sugar into a isotonic drink mix?
glucose is hypertonic, so if you add it to a 6% drink mix you’re ending up probably over 10%. So very much not hydrating
Your drink mix contains 60g of carbs?
I only have some SIS hydration drink mix, and that has only 36g of carbs per 500ml for 6% tonicity. So you’d probably be looking at similar figures, ie. drink your 60g of carbs with 1000ml of water and some salt.
No. 1 litre water + sodium + 40g maltodextrin + 20g fructose = 6%. = isotonic. Question is will only drinking that mixture suffice or will I get dehydrated ( when compared to drinking the Same volume sans carbs.
Anyways, assuming the sodium level stays constant, removing the sugars will turn your drink into a hypotonic mix, which is hydrating.
Once you add back the carbs. the osmolarity goes up, first into the isotonic range, and then hypertonic - which is when it stops being hydrating. However, note that glucose does aid in the absorption of salt so having some carbs is going to be more hydrating than just a pure saline drink.
Finally, hydration isn’t purely about the tonicity of the drink. The idea is to replace what was lost, so if a lot of sodium was lost via sweating, then that should be top priority.
I add a ton of salt as I tend to be a salty sweater. Right now I have the mix right with just electrolytes and water, I just want to make sure adding the carbs won’t adversely effect my hydration. I used the calculator and the result was;
Osmolarity (mOsmol/L) 155 (<295) Hypotonic
But I’m not sure if lower means more or less hydrating. Yeah, I’m not that bright.
Yup it’s still hydrating. As long as the osmolarity is below 295, it’s still hydrating. Sorry it’s so complicated, but I think the details are quite useful because often we want as much carbs as possible as fuel while still keeping it’s ability to hydrate.
if lower means more or less hydrating
It’s sort of a hard cutoff. Below 295, it is hydrating, above it, it’s going to cause water to come out of your cells.
A lower number doesn’t mean it’s more hydrating than a higher number. Pure water is 0, and it’s not the most hydrating drink. In the podcast I linked above, Peter mentions that the most hydrating drink contains a 2:1 ratio of glucose to sodium (in millimole concentration).
So using your 40g maltodextrin + 20g fructose formula, that’s around 1200mg of sodium. But that’s just a number, and if you lose a lot of salt by sweating and you’re only carrying two bottles, then it’s probably more important to replenish the salt than creating the most optimum drink.
First off thanks so much for taking the time to help me understand! You’ve been so helpful. In regards to sodium I typically use 1000mg total across four 1 litre bottles on a 4 hour ride. I’ve just started playing with the carb in bottle thing. Mainly to cut costs on gels and to try and up my carb intake. How did you come up with the 1200mg number? Or will it become clear when I listen to the podcast?
Awesome! Which site is that? I’d love to check it out. Also, I’ve heard jonathan talking about sodium citrate, what’s the benefit of difference over table salt? Thanks again! Oh and I need to find some lemon crystals.