Yesterday I rode a beautiful session. 2h30 of “Cornerman Protocol” on Zwift. Sweet spot blocks at 185 watts, when I was scraping to hold 170W last week. Legs on fire. Head made of steel. I felt untouchable.
Then I got off the bike. And I ran to the toilet.
What happened next stays between me and the porcelain, but let’s say I repainted the bowl in Jackson Pollock spray mode. No stomach pain, no nausea. Just water. Water under pressure.
Why? Because I played chemist with my own drink mix, and I lost.
The autopsy: 150g of brown sugar
I was making my “Poor Man’s Fuel”.
- 1.5 litres of water.
- 150g of brown sugar, because the caramel taste is good.
- A pinch of salt, eyeballed.
On paper that’s 100g of carbs per litre. Heavy, but the pros do it, right? Except I’m not a pro, and brown sugar is not maltodextrin.
Mistake 1: the osmolarity red zone
150g of sugar in 1.5L is a 10% concentration. The physiological ceiling for fast gastric emptying sits between 6 and 8%. Above 8%, your drink turns hypertonic.
When that syrup landed in my gut, my osmoreceptors screamed. It was far more concentrated than my blood. To restore the balance, my body did the exact opposite of what I wanted: instead of absorbing the water from the bottle, it pulled water out of my blood and into my gut to dilute the sugar (see the piece on hydration).
I flooded my own colon with my own plasma water. Hence the pressure washer.
Mistake 2: brown sugar, the laxative
Brown sugar carries mineral impurities that push the osmotic load higher still. On top of that it’s pure sucrose (glucose + fructose, bonded). Hydrolysis needs water. More water stolen from my blood.
Mistake 3: not enough salt
I used “a pinch”. That was ridiculous. Without enough sodium, the SGLT1 transporters, the ones that carry glucose and water into the blood, run at idle. The sugar stays in the pipe. The water stays in the pipe. And all of it leaves through the emergency exit.
The double penalty: 17% cardiac drift
The worst part? Not the toilet run. What it did to my performance.
On the Zwift file it’s blatant: 185W at 145 BPM at the start of the session, 185W at 168 BPM at the end. A 17% cardiac drift. That’s massive.
Why was my heart beating that fast? Because my blood volume had dropped. Part of my plasma was busy diluting brown sugar in my belly. Less blood = less stroke volume = the heart pumps faster to hold cardiac output.
I finished the session on willpower alone. Physiologically, I was tearing myself apart.
The repair protocol
Done playing. Here’s the recipe the science validates (and now my gut too):
- White sugar (or malto): no brown sugar, no honey, no “natural” stuff that ferments. Refined.
- Dose: max 60g to 80g per litre (6-8%). Want more carbs, eat them on the side. Don’t load the bottle.
- SALT: non-negotiable. 1.5g of salt per litre. It has to taste faintly salty. That’s the key that opens the cell door.
Conclusion
You’re not a pro because you have watts. You’re a pro when you can run your own internal chemistry. Yesterday I had the watts. I also had the chemistry of a four-year-old mixing everything he finds in the kitchen.
Next time you feel like playing chemist, respect the doses. Or get the toilet paper ready.
Cornerman, out.