Fuel When It Matters: Why Carbs and Quick Sugars Still Win in Performance
As a coach, I’ll be the first to state: you don’t need carbs all the time—but when you need them, you really need them.
There’s a growing trend toward low-carb and fat-adapted training, and yes, there’s a place for metabolic flexibility. But when intensity rises—whether that’s a hard climb, a surge in a race, or a finishing kick—your body doesn’t reach for fat. It reaches for carbohydrate.
And if you don’t have it available, performance drops. Fast.
Carbs = High-Octane Fuel
At moderate to high intensities, carbohydrates are the preferred fuel source for working muscle. Glycogen stored in muscle and liver is what allows you to sustain pace, produce power, and respond to changes in effort. (PMC)
When you train or race without adequate carbohydrate availability, you limit your ability to:
Maintain intensity
Produce repeat efforts
Finish strong
This is why carbohydrate intake during endurance exercise consistently improves performance and capacity—especially in sessions longer than 90–120 minutes. (PubMed)
Even more simply: carbs let you use the fitness you’ve built.
Quick Sugars: Not the Enemy—A Tool
There’s a difference between daily nutrition and performance fueling.
Quick-acting sugars—glucose, sucrose, maltodextrin—get a bad reputation in general health conversations. But during training and racing, they’re exactly what you want.
Why?
Because they:
Maintain blood glucose levels
Spare muscle glycogen
Delay fatigue
During prolonged exercise, consuming 60–90g of carbohydrates per hour allows you to sustain higher output and avoid the drop-off that comes with glycogen depletion. (PubMed)
And when glycogen runs low, fatigue isn’t subtle—it’s a wall.
The Hidden Cost of Going Too Low-Carb
Let’s talk about what happens when carbs are chronically too low for your workload.
1. Reduced Performance Capacity
Low-carb intake reduces glycogen stores. That means less available fuel for higher-intensity work, which directly limits endurance performance. (ScienceDirect)
You might feel “fine” at easy pace—but you’ve taken away your top gear.
2. Elevated Cortisol and Stress Load
Training is already a stressor. When carbohydrate intake is insufficient, the body compensates by increasing stress hormones—especially cortisol.
Research shows that carbohydrate ingestion during exercise can significantly blunt cortisol response, meaning less physiological stress for the same workload. (PMC)
Chronically elevated cortisol leads to:
Poor recovery
Increased fatigue
Hormonal disruption
That’s not a badge of honor—that’s a performance ceiling.
3. Muscle Breakdown and Loss
When glycogen is low, your body still needs fuel. One of the ways it compensates is by increasing protein breakdown.
In plain terms: you start burning muscle to support training.
Low carbohydrate availability has been shown to increase protein oxidation and impair muscle protein synthesis, which can limit recovery and adaptation. (PMC)
So while you think you’re getting leaner or more “efficient,” you may actually be losing the very tissue that makes you stronger and more durable.
4. Increased Injury Risk
Now connect the dots:
High cortisol
Poor recovery
Muscle breakdown
Reduced training quality
That combination leads to one place: injury.
When you can’t recover, tissues don’t remodel properly. When you can’t hit intensity, mechanics change. When you’re under-fueled, resilience drops.
You don’t just lose performance—you lose consistency. And consistency is everything.
The Smarter Approach
This isn’t about eating carbs all day.
It’s about using carbs strategically.
Low intensity day? You can go lighter on carbs.
High intensity session or long effort? Fuel it.
Race day? Don’t gamble—bring the carbs.
Carbohydrates before, during, and after exercise help maintain blood glucose, preserve glycogen, and support recovery between sessions. (PMC)
That’s how you train hard, recover fast, and show up again tomorrow ready to go.
Coach’s Bottom Line
You don’t win races—or even workouts—by proving how little fuel you can survive on.
You win by having the right fuel at the right time.
Carbs are not the enemy. Misusing them is.
Use fat for efficiency. Use carbs for performance.
And when it’s time to go—make sure you’ve got the fuel to actually go.
Train smart and go fast!
Joe
References
Cermak & van Loon (2013). Carbohydrates as an ergogenic aid. (PubMed)
Henselmans et al. (2022). Carbohydrates and performance. (PMC)
Clinical Nutrition ESPEN (2025). Carbohydrates and endurance performance. (ScienceDirect)
American Journal of Clinical Nutrition. Glycogen and endurance. (ScienceDirect)
Puta et al. (2023). Carbohydrates and cortisol response. (PMC)
Nutrients Journal (2023). Carbohydrate timing and endurance. (PMC)