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Sep 2019
12:08pm, 9 Sep 2019
8,579 posts
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larkim
Do we absorb all the calories we eat? Just using the slightly unpleasant picture of a sweetcorn input, I'm pretty damned sure that no matter how many calories are in a kernel of sweetcorn, much of it remains utterly undigested and leaves my body unused.
Does such a thing happen to other calories / carbs that we consume?
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Sep 2019
12:54pm, 9 Sep 2019
5,406 posts
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Northern Exile
You're dead right. Our bodies leave a lot of food unprocessed, particularly if you overdo it on red meat etc. People who have GI tract issues quite often take [expensive] supplements that contain enzymes that help break down food more easily. I've often wondered if these would be useful in a ultra-distance scenario.
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Sep 2019
12:57pm, 9 Sep 2019
1,196 posts
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oumaumau
You'll digest what you can larkim - sweetcorn, like tomato skins is made of cellulose and since we don't use our appendix anymore we can't break it down. Readily available calories such as sugars are digested readily, but if you take in more than you have capacity (functional receptors in the gut) for, you'll bloat.
Whether you would eventually pass it without digesting, I don't know.
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Sep 2019
1:00pm, 9 Sep 2019
8,581 posts
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larkim
How does that factor into carb calcs then? If a triple whammy of three gels in an hour gives 60g of carbs, and our bodies can "in theory" absorb 60g of carbs per hour, are we inputting 60g only to make just (sa) 90% / 54g of carbs actually useful?
I imagine also when GI issues arise, far fewer of the carbs are absorbed too? Hence my approach has always been to fuel early in a marathon, when my gut is still unstressed and welcoming, rather than later on when I might feel I need extra fuel, but my body has already started shutting down bits of the GI system which would mean I either don't absorb as well, or I just waste it as it exits the northern or southern route (!) without being digested at all.
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Sep 2019
1:02pm, 9 Sep 2019
8,582 posts
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larkim
Agreed about the sweetcorn - but the nutirion calcs will be on the basis of a lab experiment validating the energy store of corn as a whole etc. So there will necessarily be a difference between what I eat and what I reject. Clearly far less relevant for simple sugars / carbs etc, but for more complex foodstuffs it becomes more of an issue when trying to do the calculations for how much food to take with you, presumably?
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Sep 2019
1:37pm, 9 Sep 2019
1,197 posts
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oumaumau
To the first part of the first post, nope. It means if you have 60g of carbs, you're going to need 600 ml + of water to make it digestible. Apparently 'elites'/outliers can handle 10%+ (full sugar coke is 14% apparently) without gi distress.
Second part of the first post, I suppose that makes sense. You've probably got more water in your stomach/gi tract at the start of an event too ;).
Second post. Yes, calorie counts for food are done by burning (think the milican specific heat experiment form school)- not that close to digestion. It also doesn't account for the esters created by your gut bacteria as they digest the food you don't...
I don't plan based on this though, I have a fair idea from experience what I'll want to eat and when so use that knowledge. Doesn't always stop me carrying gels/food that I just didn't fancy on the day from the beginning to the end.
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Sep 2019
1:42pm, 9 Sep 2019
1,198 posts
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oumaumau
And form the previous page, there is no hope of eating to keep up with energy use - you'll always be in deficit. If you're running hard then it's important to take on sugars to feed your brain which should keep you focussed, while you can feed you muscles with a higher percentage of fat.
Fat takes around twice as much oxygen to provide fuel, and is pretty poor food for your brain.
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Sep 2019
1:50pm, 9 Sep 2019
5,408 posts
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Northern Exile
Wise words ..... starting to like this thread a lot!
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Sep 2019
1:56pm, 9 Sep 2019
8,587 posts
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larkim
Grand stuff! I'd never put the liquid + carbs stuff together in my head as being so related - I'd (daftly!) assumed that the carbs were fuel and the water was for hydration, but it makes perfect sense that they work hand in hand to transport the nutrition into the system.
I've only rarely (twice) raced longer than 3hr30, and never longer than 6hrs so I know I've always got plenty in reserve, compared to those who do 24+ hour events. I don't even want to consider what that feels like from a nutrition perspective!!
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Sep 2019
2:13pm, 9 Sep 2019
1,199 posts
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oumaumau
It's probably not as key to get the balance perfect for shorter faster stuff larkim, most will feel fairly crap for the last (half) hour of a fast marathon but can still get it finished, then deal with the consequences later (hot snakes etc.).
For longer events the hole just gets deeper (calorie deficit), but the slower pace means you can recover from one pie too many by having one less in the next hour or two..
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Amount of salt to put in some water for a long run
Jul 2020
