---
title: "Dehydrated? Your carbs are working ~16% less hard."
date: 2026-08-02
categories: ["Fuelling","Hydration & heat"]
url: https://www.semiprocycling.com/digest/dehydrated-your-carbs-are-working-16-less-hard
author: Damian Ruse (SEMIPRO Cycling)
---
# Dehydrated? Your carbs are working ~16% less hard.

[Listen to this issue as a podcast](https://www.buzzsprout.com/6262/episodes/19583844)

You have packed the gels, you are taking in around 60 g of carbohydrate an hour, and an hour into the ride the fuel still feels like it is not landing. The instinct is usually to reach for another gel. The missing part may be fluid.

A new study had nine trained male cyclists and triathletes complete two 160-minute rides. Carbohydrate intake was matched at 60 g/hr. The difference was fluid intake: riders finished one trial at roughly 0.2% body-mass loss and the other at roughly 2.8%.

When dehydrated, riders oxidised about 16% less of the glucose they had ingested. Average exogenous glucose oxidation fell from 0.61 to 0.51 g/min, and the gap began opening after around 60 minutes at only about 1% body-mass loss.

That does not mean more water fixes everything, or that more carbohydrate compensates for under-drinking. It means the two plans cannot be separated. Fluid helps determine how much of the fuel you swallow becomes usable fuel.

**For the time-capped rider:** on warm rides longer than an hour, do not skip the bottle because the ride feels short. Protect the carbohydrate you already paid for.

**For riders over 50:** treat hydration as part of the fuelling plan, not a comfort extra.

**For performance-focused riders:** rehearse fluid alongside higher carbohydrate intakes. Raising carbs without matching fluid does not guarantee more usable fuel.

**One-line takeaway:** under-drink and you are paying full price for carbs that only half-arrive.

*Source: Macrae HZ et al. Exercise-induced dehydration decreases exogenous glucose oxidation during prolonged cycling in a temperate environment. J Appl Physiol. 2026. PMID 42420769.*

## On my mind: Eat and drink for the work in front of you

The conversation I keep having with riders is about the meal before the ride: too much protein, not enough carbs, and hydration treated as something you will sort out on the bike.

Protein is a repair agent. Before the ride, your body wants glucose topped up before you start burning through it, and it wants fluid on board while it uses it.

Carbs and fluid are not two independent boxes. This study is a clean reminder that at around 1% body-mass loss you may already be leaving carb work on the table, even when the dose is right.

Nudge for the week: pick one long ride and plan the fluid exactly as you plan the fuel. Bottles counted, timings set, next to the gels rather than underneath them.

— Damian