Does gastric absorption math work?
A little background: I have done 3 IMs and have definitely struggled with nutrition, facing nausea on every course and wondering if I would even finish 2 of my races. Then I joined EN, watched the nutrition webinar and decided to revamp my nutrition. I've been testing all the products suggested like Perform, gels, bloks, etc., and spending a ton of money on all this stuff.
As I've worked on my plan, I got curious about the math and found that I typically consume 48oz. of Perform during an hour workout on the bike. I consume about 2/3 of this or 32oz./hour when I run, mostly because I can't drink as much due to the intensity. Then I looked at some of the gastric absorption research and found that the stomach only clears from 20-40oz. of liquids per hour depending on the study and some of the characteristics of the liquid. Also, the stomach only has about a 32oz. capacity. So, my pea brain says if I drink 48oz., at best I will clear 40oz. and be left with 8oz. in my stomach at the end of the first hour. I am fine for 2-3 hours doing this, but after 4 hours, I now have 32oz. in my stomach. I can't drink any more period. I am all full and have to wait for my stomach to clear before I can put in any more liquids.
This has implications:
I could feel okay until the 5th hour; then I will start to feel sick because my stomach is at capacity.
High effort may reduce stomach clearing and bring on nausea sooner.
Starting the swim on a full or nearly-full tank is a good strategy for absorption.
Drinking right out of the water is a good strategy because the stomach is nearly empty.
I am completely clueless and am making a big boo boo.
Any thoughts?
Comments
I guess my first question to you is whether you had been taking in 48 oz of Perform in the past, or ever since watching the nutrition webinar and revamping nutrition? So is your question one where you are finding you need that much Perform for sodium needs, but that the math doesn't quite work out, and thus you are questioning the approach? How often do you need a bio break when consuming that much Perform?
I'd also say you'd start to feel sick before the 5th hour - I'd guess that even ~1/2 full (possibly less), the sloshing around would be noticeable.
Another note - starting the swim on a full tank or nearly full is probably not a good idea. Perhaps you meant to specify on an empty or near empty tank? One of the things RnP talk about RE: fueling immediately before the event is to take in some sports drink about 2-3 hours before the start, to give it time to work its way out of the stomach, but so that you still have topped off energy stores.
I guess my main question is: when you revamped your nutrition, what was it before, what did you hear/realize needed changing, and what is it now?
Sounds like you may do well with some solids vs all liquids.
I by do means will try to dive into the physiology of how the gastrointestinal system works but after 13 years of racing I have my race day nutrition down and it's at about 700 cals/hour!!! No joke. Solids, liquids, and a mix of Roctane. Not sure why Roctane specific but other GU's nausea me and this one hits me pretty rock solid. I did the Infinite for sometime but realized I could do fine with Petform and it was free all day long on the race course.
It's a trial and error thing my friend it truly is. I wish you the best and hope you find the answer your seeking.
Assuming a deficit of 8oz/hr., an athlete will easily lose 5.5 Lbs. or about 3.7% of their body weight over the course of an 11 hour IM under mild conditions. I must still be a noob because this is kind of a revelation to me. Okay, thanks for hearing me out. It helped me.
IMO doing a sweat test inside at 85% FTP is not going to give you the data to be applied to an IM bike that will be done outside and at 70-75%FTP. The sweat test should mimic the race conditions as close as possible. That will give you your baseline.
I think fluid replacement is like calorie replacement you really can't replace them 1 for 1 while racing or training without slowing down substantially. Experiment with both to see how many calories and how much fluid you can replace without it affecting your gut and performance too much.
http://home.trainingpeaks.com/races/ironman-world-championship-kona/2012.aspx
Our stomachs and GI systems don't do math. I wish they would. It would simplify a lot of things.
Fluid, calories, and sodium/electrolytes are three separate parts of your race nutrition plan. I'm presuming you are talking only about fluid.
I find that most of my athletes can take in 20 - 48 oz of fluid per hour. Yes, you'll probably become dehydrated but the goal is to minimize the dehydration over the race. Including carbohydrates and electrolytes in the fluid solution does increase the absorption rate.
You have to play with it to see what your body can and will take in fluid-wise and how that changes when you add carbohydrates and/or electrolytes.