Rethinking Carbs: The Dirty Secret Behind Endurance Nutrition
- Dr. Scott Christie
- Jul 25
- 4 min read
How Much Carbohydrate Do You Really Need for Endurance Training?
When it comes to fueling long training sessions or races, most athletes hear the same advice: eat carbs, and keep eating them. But the real story is more nuanced. While carbohydrates are a primary energy source, your body also relies heavily on fat. And in many cases, training your body to efficiently use fat should be a higher priority.
Let’s unpack what the latest research, especially from the past decade, reveals, and how it impacts both performance and long-term health.
Your Body Runs on Two Fuels
Whether you're running, cycling, swimming, or rowing, your body depends on two primary fuels: fat and carbohydrates. Carbs deliver quick energy but are stored in limited supply. Fat, on the other hand, is abundant, even in lean athletes, and can power hours of steady effort.
The more efficient your fat metabolism, the less dependent you’ll be on external fueling during workouts. Building this metabolic flexibility should be one of your main training goals. It involves developing your aerobic base, aligning nutrition with your training, and using carbohydrates strategically, not reflexively.
When Carbohydrates Help Performance
Carbs definitely enhance performance during long or high-intensity sessions, but only when used wisely. According to research from Jeukendrup, Thomas, and others, here’s a general guide to carbohydrate needs based on workout duration:
These are guidelines, not hard rules. Use the smallest effective amount depending on your pace and effort level.
Individual Needs Vary
Some athletes perform well on lower carbohydrate intake, especially those who’ve trained their bodies to burn fat more efficiently through consistent Zone 2 work and lower-sugar diets. Others, especially those doing very intense efforts, may require more.
Still, many athletes overestimate their carbohydrate needs. For sessions under 90 minutes, especially at moderate intensity, your stored glycogen is often more than sufficient.
Carbs and Gut Issues
Gastrointestinal distress is common in endurance athletes during long events. Symptoms like nausea, cramps, bloating, and diarrhea affect 30 to 60% of athletes. Why? During intense efforts, blood flow shifts away from the digestive tract, making nutrient absorption harder.
Some athletes also have difficulty absorbing sugars or have underlying gut sensitivities. One study found 70% of runners struggled to absorb sugars during extended activity. In rare cases, high-carb intakes can trigger gut inflammation or even bleeding.
The upside? Like muscles, your digestive system can adapt. "Gut training", gradual exposure to fuel during workouts, can reduce symptoms over time.
Can Too Many Carbs Harm Your Health?
Here's where things get serious. Carbs may help performance, but overusing them, especially simple sugars, can lead to health issues, even in fit athletes.
A 2023 study by Dr. Tim Noakes found that 3 in 10 middle-aged endurance athletes developed prediabetic fasting glucose levels after just 31 days on a high-carb diet. When switching to low-carb, both blood sugar and fat metabolism improved significantly.
This wasn’t a fluke. Other studies show similar trends. Some athletes using continuous glucose monitors show disrupted glucose control, even while training consistently and appearing healthy.
The concern isn’t about carbs alone, but about chronic overconsumption of fast-digesting carbs outside of training. Being fit doesn’t always equal being metabolically healthy.
Smarter Carbohydrate Strategy
Cutting carbs isn’t the goal, metabolic flexibility is. That means being able to efficiently burn fat most of the time, while still tapping into carbs when needed.
Here are some practical tips:
Use carbs during long races or high-intensity workouts, not for every session.
Occasionally train in a fasted state to enhance fat-burning ability.
Match your carb intake to your training volume, rest days don’t require racing-level fuel.
Favour complex carbs like oats, lentils, and berries when not training.
What This Means for You
If you train for endurance events regularly, understand that more carbs aren’t always better. You need a smart balance, one that supports both performance and long-term health.
We now know that up to one-third of athletes may show early signs of blood sugar issues when carbs are overused, especially with age or during off-season periods when training volume drops but diet doesn’t adjust.
The Bottom Line
Carbohydrates are performance tools, not requirements for every session. Prioritize fat-burning, use carbs strategically, and fuel in sync with your actual training needs. It’s a balanced, sustainable approach that supports your performance goals and protects your metabolic health for the long haul.
Ready to Train Smarter, Not Just Harder? Start optimizing your fuelling strategy today.
Book your Free Consultation with us to discuss metabolic flexibility and learn how to balance carbs and fat for peak endurance and long-term health.
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