Carbs Aren’t the Enemy: Why Low-Carb Diets Hurt Endurance Athletes

Carbs. The most misunderstood macronutrient in endurance sports.

Some athletes fear them. Others avoid them. Many have been told that cutting carbs is the key to improved performance, fat loss, and metabolic efficiency. But let’s set the record straight: low-carb diets and endurance training don’t mix well for most athletes.

In fact, going low-carb can tank your training, slow recovery, and make you feel like you’re running through quicksand instead of crushing your workouts. Carbs are not the enemy—they’re the fuel that keeps your engine running.

Today, we’re diving deep into the science, common myths, my personal take, and action steps so you can fuel right and perform at your best.

The Big Carb Confusion: Why Are Athletes Avoiding Carbs?

Over the past decade, low-carb diets like keto and paleo have taken over the fitness world. These diets promise fat loss, better metabolic health, and increased fat-burning capabilities. And yes, for the average sedentary person, eating fewer refined carbs and processed junk can be a good thing.

But endurance athletes? That’s a different story.

When you’re running long distances, cycling for hours, or doing back-to-back training sessions, you need fuel that can keep up. And guess what? That fuel is carbohydrates.

Here’s why so many endurance athletes mistakenly cut carbs:

❌ They fear weight gain. (But carbs don’t inherently make you gain weight—overeating does.)

❌ They think fat-burning = better performance. (Fat is a slow fuel source, not ideal for race-day intensity.)

❌ They’ve been told, “carbs cause inflammation.” (Not true. Processed junk food does, but whole food carbs? Nope.)

❌ They hear about elite athletes experimenting with low-carb diets. (But those athletes are exceptions, not the rule. And even they cycle carbs strategically.)

The reality? Most endurance athletes who cut carbs end up exhausted, underperforming, and wondering why they feel like garbage in training.

The Science: Why Carbs Are

Essential for Endurance Performance

Let’s break this down:

1. Carbs = Your Body’s Preferred Energy Source

• When you eat carbs, they’re broken down into glucose and stored as glycogen in your muscles and liver.

• During workouts, your body taps into these glycogen stores for quick, efficient energy.

• The harder and longer you go, the more your body relies on carbs.

2. Endurance Athletes NEED High Glycogen Stores

• Research shows that depleting glycogen stores leads to early fatigue, reduced power output, and increased perceived exertion. (PubMed)

• A well-fueled endurance athlete will have higher muscle glycogen, meaning more stored energy for race day.

• Once glycogen is gone, your pace slows, your form suffers, and your brain begs you to quit.

  
  

3. Low-Carb = Increased Stress Hormones & Muscle Breakdown

• Low-carb training can increase cortisol (your body’s stress hormone), leading to poor recovery and higher injury risk.

• Without carbs, your body may start breaking down muscle tissue for fuel—which is the LAST thing an endurance athlete wants. (GSSI)

  
  

Low/No-Carb Diets For Some in Endurance Sports

It’s important to recognize that while low or no-carb diets (such as ketogenic or carnivore diets) are NOT optimal for endurance performance, they can be effective for certain athletes depending on their goals, body type, and sport.

Who Might Benefit from a Low-Carb or Ketogenic Diet?

✅ Ultra-endurance athletes: Some ultra-endurance runners, long-distance cyclists, or mountaineers use low-carb diets to become more "fat-adapted," relying more on fat for fuel during low-intensity, long-duration efforts.

✅ Athletes prioritizing weight loss: If weight management is a primary goal, lowering carb intake can help control appetite and improve metabolic flexibility.

✅ Athletes with metabolic conditions: Some athletes with insulin resistance or type 2 diabetes find that reducing carbohydrate intake helps regulate blood sugar and improves overall metabolic health.

Who Should Avoid a Low-Carb Diet?

❌ Athletes who need explosive power and speed (e.g., sprinters, triathletes, marathoners, swimmers)

❌ Athletes doing high-intensity training or interval work

❌ Anyone struggling with low energy, poor recovery, or declining performance

While some endurance athletes have successfully adapted to low-carb diets, research shows that high-intensity performance is still impaired without adequate glycogen. A meta-analysis found that ketogenic low-carbohydrate, high-fat diets do not improve endurance performance and often decrease exercise efficiency. (PubMed)

How to Fuel Right: My Endurance Carb Strategy

🥯 Daily Carb Intake:

• 6–10 g per kg of body weight per day for endurance athletes. (GSSI)

  • This would be 2-5 g per lb of body weight.

• Adjust based on training volume—longer/harder days need more carbs.

  
  

🍚 Pre-Workout (1-3 Hours Before):

✅ Oatmeal + banana + peanut butter

✅ Whole wheat toast with honey & almond butter

✅ Rice + eggs + avocado

⚡ During Long Runs/Rides (>60 min):

✅ 60-90g of carbs per hour

✅ Options: Energy gels, sports drinks, bananas, dried fruit

🥩 Post-Workout Recovery (Within 30 Min):

✅ Carbs + Protein = Optimal Recovery

✅ Chocolate milk, protein shake + fruit, rice + lean meat

My Personal Take on Carbs & Endurance Training

As a coach, I HATE seeing athletes struggle because of misinformation.

🔴 I’ve worked with runners and triathletes who were stuck in constant fatigue, slow race times, and poor recovery—all because they weren’t fueling properly.

🔴 They were afraid of carbs, thinking they needed to be leaner or more “fat-adapted.”

🔴 Once we reintroduced strategic carbs, their energy skyrocketed, their paces improved, and their training felt easier.

Carbs are NOT the enemy.

✔️ They are the difference between struggling through training vs. thriving in it.

✔️ They fuel your endurance, speed, and recovery.

✔️ They help you run faster, push longer, and feel stronger.

If you’ve been limiting carbs and wondering why training feels WAY harder than it should, I challenge you:

🔹 Add more quality carbs to your diet.

🔹 Track your energy levels, performance, and recovery.

🔹 Notice the difference. I promise, your body will thank you.