Hi Zack,
Thanks for the generously kind words. Glad to hear your fueling game is a strength now. :)
There is no fixed limit to the rate at which you can consume kcal while exercising. Chrissie Wellington famously did 500+ kcal per hour on the bike leg of her final win at world champs almost 20 years ago, under the tutelage of Dr. Asker Jeukendrup. And a fair bit of that was
not carbs. Most was carbs, of course. But it's here in the forum somewhere. And IIRC there were close to 100kcal from fat and protein. I'm not sure if this was intentional, tbh.
Back to your question, yes, there is a balance of consumption and exercise rate where you can begin to out-consume your kcal burn. It sounds like you're already within 100kcal of that crossover, which is absolutely an advantage in a 40-hour continuous exercise feat. To maximize the kcal you can consume, minimize fiber for sure, and keep protein and fats near zero, too. Aim for just glucose and fructose sources.
For breakfast, yep, absolutely slam high-carb, high-palatability everything that you've consumed pre-training before race day.
In both cases - breakfast, and intra-race - hydration is a critical component of your gut tolerance and ability to digest large quantities of carbs quickly. A hydrated gut is a happy gut. This means it needs to be hydrated inside and out. The 'inside' hydration just means drinking fluid with carbs, always on race day. The "outside" aspect of gut hydration is just a reflection of your overall body hydration status. Get dehydrated and gut function is going to collapse substantially. It will hard to regain gut function once it's gone due to dehydration. It requires slowing down for a while, and pushing fluid and electrolytes sufficiently to regain hydration already lost on the trek. Not a good scenario.
If you find that you can get your fueling with 50kcal of race kcal burn rate, yeah you probably could perform almost identically with or without breakfast. I totally made that number up, and don't quote me. That said, here's an alternate strategy:
- Wake up to the softest alarm possible & no lights on, 2.5-3 hours pre-race. Eat a couple hundred grams of tasty carbs with 16oz water & 500-1000mg sodium.
- Go back to sleep immediately. Do not turn any lights on.
- Wake up to a second alarm much closer to race time. As close as possible if you're trying to maximize pre-race sleep.
- When your alarm goes off this second time, again consume carbs, water, and sodium, but this time, flip all the lights on immediately and don't stop consuming carbs, sodium, and water until you finish the race 40.5 hours later. :) Keep on sipping and consuming! Maybe an extra-big glug right before you dive in for your first real arm stroke in the swim leg. Goal: sustain your blood sugar, sodium and hydration as long through the swim as possible. :)
Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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