April 21, 2026 · 5 min read

Fizzy Drinks and Cycling Training — Why It's Worth Giving Them Up

Fizzy drinks before and during a bike workout put CO2 into your stomach, which — in a cycling position (torso bent forward, pressure on the diaphragm) — makes it harder to breathe fully and encourages burping and bloating. In practice this means less comfort during efforts above the aerobic threshold and a real, though hard to measure directly, drop in available power.

What CO2 does in your stomach during exercise

The carbon dioxide dissolved in the drink is released in your stomach and stretches its walls. At rest, that is just discomfort. On the bike, where your torso leans forward and the diaphragm has less room to work, the same gas takes away breathing capacity you would otherwise use for full breaths at a high breathing rate (30+ breaths/min at an intensity close to FTP).

Does a fizzy drink really lower your power on the bike?

Directly — there are no studies counting the watts lost to CO2. Indirectly — yes: shallower breathing at the same intensity raises your perceived exertion (RPE) and shortens the time before you drop off the target power. If your trainer data shows power fading in the second half of an interval despite a steady heart rate, it is worth checking what you drank 20–30 minutes earlier.

Sugar and phosphoric acid — the second problem

A classic cola has about 10.6 g of sugar per 100 ml — in a 500 ml bottle that is over 50 g, as much as a good energy gel, but without electrolytes and with added phosphoric acid, which in some people makes reflux worse in a bent-over position. A sugar-free diet drink solves the energy problem, but not the gas problem.

Is a sugar-free (zero/light) drink safe on the bike?

In terms of energy, yes — it provides no carbohydrates, so it will not disrupt your fuelling plan for the session. In terms of stomach comfort, no — it is still carbonated, so the bloating and burping problem remains.

When a fizzy drink actually hurts your results

• Threshold and VO2max intervals — every restricted breath at a high breathing rate matters more than at an easy tempo.
• Long rides in the heat — gas and sugar slow gastric emptying, which gets in the way of taking in carbohydrates regularly every 20–30 min.
• Races and FTP tests — stomach discomfort during a 20-minute test can lower your result by a few percent, because you shorten your breath instead of deepening it.

What to drink instead

On short, easy rides — plain water. On longer and harder ones — an isotonic drink or water with electrolytes and liquid carbohydrates, without the fizz. If you want sugar + caffeine before a race, a gel or a ready-made sports drink will work better than a cola straight from the fridge just before your warm-up.

How long before training should you stop drinking fizzy drinks?

At least 60–90 minutes, so the gas has time to partly leave your stomach before the warm-up. If you drink it during the ride — simply switch to the still version of the same drink or to an isotonic.

How to check it in your own data

A single bad session proves nothing — too many variables (sleep, TSB, temperature) affect power on any one day. To check the real effect, compare series of workouts with a similar structure and intensity with and without a fizzy drink beforehand, looking at how well you hold power in the second half of an interval relative to the first. If the difference is systematic rather than random, you have your answer without guessing.

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