“I was in this vicious cycle of my stomach being upset, not wanting to take carbs, and just forcing my carbs down because my legs were dying.”
If you’ve been there, you know exactly what that feels like. Your legs are begging for fuel, your stomach is refusing it, and every sip feels like a negotiation. Another athlete put it more simply after a long race: “I don’t think I’ve ever felt so bloated in my life.”
The usual conclusion is “I just have a bad stomach.” More often than not, that isn’t what’s going on.
In How Many Carbs Per Hour Do You Actually Need? we talked about carbs having to get through a door from your gut into your bloodstream, and how a line forms when you send more than the door can handle. This post picks up right there. What’s actually happening on the gut side of that door when the line backs up, and what you can do about it?
It comes down to concentration
I like to think of carbohydrates as Lego pieces. Your body wants to use single Lego pieces for energy, and your gut is constantly paying attention to how many pieces are floating around in a given amount of fluid. That’s called osmolality: how many pieces are in a certain volume.
Your body likes things at a fairly steady concentration on both sides of that door. So if all of a sudden one side is way too concentrated, your body will try to pull water in to dilute it and bring it back to where it wants to be. Go from two pieces to 40 pieces really quickly, and that’s exactly what happens.
That’s where the GI distress comes from. All of a sudden there’s a ton of water in your gut with a ton of stuff in it. That’s the bloating, the sloshing, the cramping in your stomach and, for some people, the emergency porta-potty stop.
Fluid and sodium are the delivery system
Here’s the part people tend to forget. Carbs don’t get from your stomach to your muscles on their own. They need enough fluid, and enough blood volume, to get where they’re going.
Sodium plays a big role here too. I think of sodium almost like the glue that keeps water in your system. People forget that one of the jobs of sodium in helping you hold on to water is so that water can help digest everything a little bit easier.
So if there’s a lot of carbohydrate and not a lot of sodium or fluid, things just kind of sit there. They aren’t really moving, and a stomach full of carbs that aren’t moving is not a happy stomach.
The flip side
It works in the other direction too. If you’re taking in a ton of fluid and sodium but not a lot of carbohydrate, you can end up with that same bloated, sloshy feeling.
That’s why “too many carbs” isn’t quite the right way to think about it. The problem is usually the ratio. Carbs, fluid and sodium work as a team, and when one of them gets way ahead of the others, your gut is the first to let you know.
Why it shows up late, and in the heat
Most athletes don’t have stomach trouble in the first couple of hours. It creeps in later. When things get past that five or six hour mark is when the stomach is most at risk of going, and heat makes it worse.
There are a couple of reasons for that. At high intensity, or in the heat, your body stops prioritizing breaking down food. Blood gets sent to your working muscles and to your skin to cool you off, so your gut is running on a skeleton crew. On top of that, you’ve been sweating for hours, so the fluid and sodium that help move carbs along are running low right when you need them most.
That’s why the heat version often doesn’t look like throwing up. It’s more of a queasiness that won’t go away until you stop wanting to eat altogether. In the heat, that’s usually a fluid and sodium story before it’s a stomach story.
What this looks like in real life
One athlete I worked with was mixing bottles at around 180 grams of carbohydrate each, on top of gels and food. They were already suspicious of it: “I’m assuming that I probably am loading my bottle so much that my body probably isn’t getting the hydration or the salt that it can because there’s too much fuel in the bottle.”
They were right. Those bottles were a little too concentrated, especially on top of all the other grams of carbs they were taking in. It wasn’t that their stomach couldn’t handle fuel. It was that one bottle was trying to do three jobs at once, and doing all of them at a concentration their gut had to fight.
What to do about it
- Look at carbs, fluid and sodium together. Instead of asking “how many carbs am I getting per hour,” ask how many carbs, how much fluid and how much sodium you’re getting per hour, and whether those three make sense together.
- Stop treating your bottle like something you have to finish. One of the most common mistakes I see with carb-heavy drink mixes is athletes arbitrarily finishing the bottle because they need to get the carbs in, while ignoring their thirst cues. If your bottle is carrying all your carbs, you’re drinking to a number instead of drinking to thirst. Moving some of those carbs into gels, chews or a flask lets your bottle go back to being something you can actually drink.
- When your stomach starts to turn, reach for salt before you reach for less. A lot of times with GI distress, adding a little extra electrolytes can be really beneficial. Sometimes the carbs are fine and they just need more help getting where they’re going.
- Keep some plain water on hand. Rinsing out your mouth or taking a few sips of water can take the edge off when everything starts tasting too sweet. It’s also great for pouring over your head in the heat.
- Never debut a new bottle on race day. If you want to try a more concentrated mix, test it on long training days first. Ideally some of those days should be hot, and some should be long enough to get past that five or six hour mark.
Your gut isn’t broken
If you’ve had a race fall apart because of your stomach, it’s easy to decide your gut just can’t handle fuel. Most of the time, it’s the mix, not the gut.
Figuring out the right ratio of carbs, fluid and sodium for the way you train and race is exactly what we work on inside the Gravel Performance Nutrition Course and in 1:1 sessions. If you’re tired of the vicious cycle, that’s a great place to start.
