You want to take in fluid that is as salty as your sweat, right?
Yes. But most drinks like Gatorade, Skratch, etc. were designed to do this. For most people those should keep anyone from getting hyponatremia even during long events with lots of sweating. And there is sodium in most food and gels. I know someone who got lab sweat testing and he was sweating so much it was nearly impossible for him to replace all the fluid he would lose but even then the problem was absorbing enough water and not a sodium deficiency.
Expanding on @matthew.weigel question…can the body process it too?
My sweat test revealed I lose almost 1500 mg/hr of sodium. I only take in roughly 750 mg/hr using Precision Hydration tablets mentioned on the podcast and thought I read that’s about the limit the body can handle anyways.
Sure, but it’s also individual. This paper for example found a ten-fold range in sweat sodium concentration, and noted
the individual player who lost 30 g/d (15 teaspoons [75 g] of table salt) had the third highest SwtR (2.94 L/h) and the highest SwtNa+ (99 mEq/L). Amazingly, replacing 30 g of sodium with the average sports drink would require nearly 65 L; this is not only impractical, but it would add 13 742 kcal and 3848 g of sugar and would cause hyponatremia.
A 280 lb guy sweating 3 liters an hour at 99 mEq per liter of sodium is so far from normal it would apply to a few people on earth. But still, blood is 140 mEq/L so if he didn’t take in anything he would be hypernatremic because he is still losing more water than salt. Then we have to consider that human kidneys are very good at holding on to sodium so if he drank water and started to dilute his blood his kidneys would work hard to hold on to sodium.
But sure, in this case where someone sweats out half of their blood volume an hour they would need both a lot of water and sodium. But they would still need to replace more water than sodium compared to the total body water and total sodium they started with.
The initial question was whether someone biking in hot weather could sweat so much they would become hyponatremic and I would again say that can’t happen unless they drink too much plain water without taking in any sodium and it would still take hours and their kidneys would try very hard to prevent it. Could they become hypovolemic or dehydrated, sure. But it would be very difficult to get hyponatremic.
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