Does fueling strategy need to change as you become increasingly dehydrated in ultra-events?

You know where you feel nauseous because there is too much sugar in your system and not enough water and you get that sort of reverse osmosis thing happening?

How do you avoid that when it’s too warm and you’re sweating profusely. Say it was an indoors ultra event so you had access to as much water as you wanted, food types etc, but the temperature is much warmer than you’re used to. And say the strategy had to work no matter 10 hours or 30 hours.

Is there a specific strategy to deal with this as opposed to fueling in temperatures you’re used to?

I hesitate to call it a strategy, but with a long rides + variable temperatures you need to uncouple your fuel and fluids. What I mean is you want to keep your calorie intake roughly constant for each hour (up to max you can tolerate), but vary the amount of water you’re taking. If it’s really hot out, you might have to mix up your bottles at a weaker concentration of mix to make up for the fact you need to drink more bottles per hour. Or go from 2 bottles of mixed, to 1 bottle mix at your “normal” concentration and 1 bottle water (still have to drink more bottles per hour).

Conversely, in cold events where sweat losses are lower you might need an insanely concentrated mix to keep enough energy coming in without overhydrating having to stop and pee every 10 minutes.

Also keep in mind, sometimes the nausea is just your palette getting sick of the drink mix flavor, or even cravings for solid foods. When looking at several hours+, I think you need to look beyond purely carbs and get some protein. 30 hours? Something resembling a real meal or 2. The specific foods end up being very individual. One tactic is to have a large variety of snack foods available so you can pick and choose depending on what sounds good at the moment.

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Do you think using gels instead of mixing powder into the water would be better?

It would make tracking simpler, for sure. X gels per hour. And vary your water intake as needed. Done. No need to do math to titrate the new bottles based on the carbs/hour you’ve recently been drinking. If it’s a purely indoor event, I like to use a weight-scale to determine my dehydration rate (which various with effort, temp, and humidity).

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This might sound crazt, but for years, when I would spend long 8-12 hour days ice and alpine climbing, I didnt want much water, for the reasons stated above, but still needed massive amounts of calories. I found that the only thing that didn’t turn into a frozen rock were Little Debbie Cosmic Brownies. Cosmic Brownies | Little Debbie. They are so cheap, they are almost free, and have 270 kcal each. Granted they have fat, and a smidge of protein. They dont quite ever freeze, until below -10 deg F. And a couple in your pocket would keep them from freezing. They don’t taste to terrible either.
As has already been said, experiment and find whst works for you. Try not to get dehydrated though. Gels freeze if its cold. :cold_face:


This makes no diff, FYI.

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I’m just back from about 80hrs riding in 8 days. Had water only in my bottles but added a half tab of electrolyte to one occasionally.
Fueled with chocolate bars, petrol station sandwiches, biscuits and at least one 1000 calorie freeze dried meal each day. These big meals gave a massive lift to my energy levels. They’d tide me over for another few hours with the occasional snack.
Drink mix or gels would have worn thin very quickly.

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Yes. Maximize fluid intake and retention by consuming maximum absorbable amount of water and sodium, that doesn’t pose GI distress, from onset of exercise.

Maximizing water intake per gut limits is key.
Maximizing sodium intake per gut limits is also key.
One without the other leads to hyponatremia or GI distress.
Without doing both, you can’t be optimally hydrated.

Optimal hydration is required for exogenous sugar/carb absorption.

Sometimes, it’s physically impossible to stay sufficiently hydrated to sustain max carb intake rates. It becomes an optimization problem. The RP Diet for Endurance goes into this.

The literature suggests that 1-1.2L fluid per hour, plus 1000-1500mg sodium per hour is probably the maximum absorbable, on average, during exercise.

I had heard that @Nate_Pearson frequently drinks 1.5-2.0L per hour.

While I was MTB’ing in Tucson in April, I was happily consuming 1.6L per hour + 2400mg sodium per hour, and feeling no GI distress, not to mention wanting more fluid and sodium. Context: Average power for these rides was very low end of aerobic with normalized power of mid-Z2. Full sun, 95 degrees. Relative exertion affects absorption capability of guts. I’m 6’1", 210.

I have not looked into evidence for linking body size to max fluid absorption ability.

There is little, if any, link between body size and carb absorption ability during exercise.

These two anecdotes lead me to believe that my water & sodium recommendations in The RP Diet for Endurance may be slightly too modest or at least too narrow, for some folks in very hot/humid environments, and that the inter-individual variability in fluid absorption rate and gut tolerance is high and probably trainable.

Holding carb consumption rate constant throughout event is likely not optimal.

Higher carb intake is possible while well-hydrated. Take advantage, so long as it doesn’t compromise hydration maintenance ability. Solutions of 8-10% carbs do little to slow down absorption ability compared to 6-8%. Since fluid volume consumption will be high, there is no need to exceed 10% carb solution. Getting close to it, in first 3-8 hours may be optimal.

It is unlikely that 10% carb solution will be optimal 10-30 hrs later when >2% body water loss is likely to have taken place. 6-8% carb solution is wise, at that point.


Aha thanks Doc, that’s the crux of it there. How did you get your sodium?

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Sodium Citrate

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Sounds great! What have you done?




Agree, he’s been fantastic anytime I’m searching for something. Completes nails it.

Ordered the sodium citrate now thanks by the way, going to do a little practising and see how far I can push it without taking a proper break…


Thanks guys. Happy to help.

I’ll be waiting for my wife to complete something silly like a double or triple Everesting challenge before we can tell you what happens to one’s body when consuming only carbs, caffeine, sodium and water for >30hrs of exercise.

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Funny you say this because that’s exactly what I’m trying to crack fuelling wise. A double to triple vEveresting.

I think in a well cooled room, or even setup outdoors in a moderate climate like a regular Everesting it becomes much more straightforward, especially if you’re planning on decent breaks.

If doing this and only using descents as ‘rest’ then it becomes much more weighted towards intelligent fuelling. You can be as strong as you like and as mentally game - but once your gut shuts down it does so catastrophically fast and you go from hero to zero in literal minutes, as I’ve recently discovered hence popping in here to mine your brain :smiley:

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