Simple vs. Complex Carbs: Which Should Endurance Athletes Eat & When?

January 14, 2026

An assortment of dry pasta varieties is spread out on a surface, with a wooden spoon resting on top.

As an endurance athlete, I’m preaching to the choir about the importance of carbohydrates. Unfortunately, there are still some who see simple and complex carbs as one and the same (all a form of energy).

Being a sports nutritionist, I talk to endurance athletes almost daily who leverage carbohydrates but aren’t truly sure about the importance of simple vs complex carbs.

Both simple and complex carbs play distinct roles in powering your performance, but choosing the wrong type at the wrong time creates energy crashes that sabotage your training. The core principle you must understand is this: different carbohydrate structures are digested at different rates and affect blood sugar in dramatically different ways.

This fundamental difference determines whether you experience steady, sustained energy or face the dreaded mid-workout crash.

There are four structured steps we’re going to look at in this article as they relate to simple vs complex carbs:

First, we will establish the chemical and metabolic distinctions between simple and complex carbohydrates.
Second, we will examine how glycogen in both your muscles and liver powers endurance performance.
Third, we will apply timing protocols for optimal carb selection before, during, and after training.
Finally, we will implement strategic carbohydrate loading while maintaining insulin sensitivity and lower rates of type 2 diabetes.

Disclaimer: This article is for informational purposes only and should not be used to treat or diagnose any condition. It is recommended that you speak with your doctor before starting any exercise program, making changes to your nutrition plan, or adding any new supplements into your current regimen.

Understanding the Difference Between Simple and Complex Carbohydrates
The Role of Carbohydrates in Endurance Performance
When to Eat Simple Carbs vs. Complex Carbs
How to Balance Carbohydrate Intake for Peak Performance
Choosing Quality Carb Sources for Sustained Energy

Understanding the Difference Between Simple and Complex Carbohydrates

Simple vs complex carbs don’t need to be overcomplicated.

Simple carbohydrates are composed of one or two sugar molecules. This short-chain structure allows rapid breakdown and absorption.

You find simple carbs in items such as table sugar, honey, candy, fruit juice, and sweetened beverages. Your digestive system processes these quickly, causing blood sugar spikes within 15 to 30 minutes of consumption.

This rapid glucose delivery creates a fast surge in energy. However, the spike triggers an insulin response that often leads to an equally quick drop in blood sugar levels. Added sugars found in processed foods such as desserts, soda, syrup, and refined grains like white flour or breakfast cereal all fall into this category.

Complex carbohydrates feature longer chains of three or more naturally occurring sugar molecules. These structures include starches and various types of dietary fiber.

According to research, up to 80% of endurance runners fail to consume adequate carbohydrates to support their training demands. This deficiency directly impairs performance.

You find complex carbs in brown rice, whole-wheat pasta, oats, legumes like lentils and chickpeas, beans, and seeds such as almonds. Vegetables like sweet potatoes and most fruits also provide naturally occurring complex carbohydrates. Whole grains retain fiber that significantly slows digestion.

This slower breakdown maintains steady blood glucose levels for extended training sessions. The presence of dietary fiber is what distinguishes most complex carbs from simple ones on a functional level.

Foods with a glycemic index below 55 are classified as low GI and cause gradual blood sugar increases. High GI foods, those scoring above 70, trigger rapid spikes. Simple carbohydrates typically rank high on the glycemic index, though not always.

For example, fructose from fruit is technically a simple sugar but digests more slowly than pure glucose. Complex carbohydrates usually have lower glycemic values, but processing methods matter. White rice, though technically complex, has a high glycemic index of 73, similar to pure glucose.

The American College of Sports Medicine recommends endurance athletes consume 6 to 10 grams of carbohydrate per kilogram of body weight daily for moderate to high-intensity training. A 70-kilogram runner requires 420 to 700 grams daily to support performance.

Both simple vs complex carbs serve critical roles when timed correctly. Simple carbs deliver quick fuel during races or intense efforts when you risk hypoglycemia. Complex carbohydrate foods supply lasting energy through slower absorption, helping maintain stable blood sugar during base training and daily activities.

Understanding this difference allows you to select the right fuel source for each training session.

The Role of Carbohydrates in Endurance Performance

Carbohydrates provide the primary fuel source for muscles during sustained, high-intensity exercise. Your body stores these carbs as glycogen in both your muscles and liver.

Muscle glycogen supplies energy directly to working muscles. Liver glycogen maintains blood glucose levels, feeding your brain and central nervous system during exercise.

During endurance activities like distance running or cycling, you burn through glycogen stores at rates approaching 1 gram per minute during moderate-intensity work. Research shows that glycogen depletion strongly correlates with fatigue development. Running low leads to what we call “hitting the wall” or “bonking.”

Studies using muscle biopsy techniques reveal that after 60 minutes of exercise at 61% of VO2max, glycogen breakdown occurs in all type I muscle fibers and approximately 65% of type IIA fibers. At higher intensities, depletion accelerates dramatically.

When muscle glycogen drops below critical levels, performance suffers measurably. A 2025 study found that glycogen-depleted muscles experienced 60 to 80% depletion, leading to significant performance decreases. Your pace slows, perceived exertion increases, and mental fatigue sets in.

Optimal carbohydrate intake depends directly on training intensity and duration. The Gatorade Sports Science Institute recommends consuming 1 to 4 grams of carbohydrate per kilogram of body mass in the 1 to 4 hours before exercise lasting more than 60 minutes.

During endurance events lasting one to three hours, you need 30 to 60 grams of carbs per hour. Common sources include bananas, honey packets, raisins, potatoes, or sports nutrition products like EndurElite Fuel Elite that utilizes a blend of carbohydrates, electrolytes, and amino acids.

When to Eat Simple Carbs vs. Complex Carbs

Timing your carbohydrate intake correctly transforms how your body responds to training and competition. The following protocols represent current best practices:

Timing	Carbohydrate Type	Purpose	Examples (Meal or Snack)	Pro Tips
1-3 Hours Before Training or Competition	Complex Carbohydrates	Provide slow, steady energy release Support stable blood sugar Optimize muscle glycogen stores	Oatmeal with banana slices Brown rice with roasted sweet potato Whole-grain bagel with peanut butter	Avoid high-sugar foods pre-race to prevent energy crashes Limit fiber intake within 1 hour of exercise to reduce gastrointestinal distress
15-30 Minutes Before Workout	Simple Carbohydrates (Small Amounts)	Deliver a rapid glucose boost for last-minute energy Prime muscles for intense effort	Half a banana Small handful of raisins Energy chews or powders like EndurElite Carb Elite	Keep portions small to avoid stomach upset Test different foods during training, never on race day
During Long Training Sessions or Races (60+ minutes)	Simple Carbohydrates	Offer instant energy to delay fatigue Help maintain intensity and mental sharpness	Sports drinks with maltodextrin and fructose Energy gels, chews, or EndurElite Fuel Elite	Aim for 30-60g carbs per hour for sessions exceeding 60 minutes Ultra-endurance athletes may tolerate up to 90 grams per hour using glucose-fructose combinations
Immediately After Exercise (Within 30 Minutes)	Simple + Complex Carbohydrates	Speed glycogen recovery at rates of 1.0 to 1.2 g/kg/hour Kickstart muscle repair Reduce muscle soreness	Chocolate milk White rice with grilled chicken Fruit smoothie with oats and protein powder	Pair carbs with protein in a 3:1 or 4:1 ratio for optimal recovery Your muscles absorb carbs most efficiently within the first 30 minutes post-exercise
Main Meals Throughout the Day	Complex Carbohydrates	Support all-day energy and metabolic health Boost fiber and micronutrient intake	Quinoa salad with beans Whole-wheat pasta with tomato sauce Sweet potato bowl with vegetables	Fill half your plate with whole grains, legumes, and vegetables These foods provide 30 grams of dietary fiber daily, supporting heart health and digestive function

It is advised that you test your fueling strategy during training sessions (never during a competition).

Many elite athletes follow a structured pattern: a complex carbohydrate breakfast 2 to 3 hours before training, simple carbs from energy products during strenuous efforts, and a combination of simple and complex carbs with protein immediately after.

This approach optimizes both performance and recovery.

How to Balance Carbohydrate Intake for Peak Performance

Strategic carbohydrate management of simple vs complex carbs requires precision and consistency. The following protocols will help you optimize carb intake across different training phases.

Daily Carbohydrate Targets

Target 45% to 65% of daily calories from carbohydrates. For most endurance athletes, this translates to 6 to 10 grams per kilogram of body weight daily.

A 70-kilogram athlete requires 420 to 700 grams depending on training volume. Ultra-endurance athletes training 4 to 5 hours daily may need 8 to 12 grams per kilogram to maintain performance.

Pre-Training and Competition Nutrition

For breakfast or pre-training meals, have them 1 to 3 hours before exercise. Choose whole-wheat bread, oats, or other starchy carbohydrates rich in dietary fiber. These provide longer-lasting energy without causing rapid blood sugar spikes.

A 2024 study of marathon runners found that most consumed only 1 gram per kilogram in their pre-race meal, falling well short of the recommended 1 to 4 grams per kilogram. This deficiency directly impacts race performance.

Carb-load one to three days before major competitions using plant-based foods like sweet potatoes and beans. Research published by the Gatorade Sports Science Institute recommends 10 to 12 grams per kilogram of body mass daily for 36 to 48 hours before events lasting more than 90 minutes.

Recovery Protocols

Pair carbohydrates with protein immediately post-workout. This combination supports muscle repair, boosts satiety, and prevents sudden blood glucose swings.

Aim for a 3:1 or 4:1 ratio of carbs to protein, as this ratio can optimize glycogen resynthesis while providing amino acids for muscle repair.

Adjusting for Training Load

On rest or taper weeks, reduce simple carbs such as candies, sweets, corn syrup, and raw sugar. Reduced activity lowers energy needs proportionally.

Maintain complex carbs from fruits, vegetables, and whole grains to help keep blood sugar steady. High-fiber foods help protect against diabetes and cardiovascular disease risks even during lower-volume training periods.

If you experience symptoms of carbohydrate malabsorption, such as constipation or diarrhea, consult a sports dietitian. This has actually happened with a few of my athletes and caused me to make changes to their nutrition protocol. For instance, it may require temporarily limiting certain sugars, such as fructose or sucrose.

I also recommend that all my athletes avoid excessive intake of simple carbohydrates outside of training windows.

Choosing Quality Carb Sources for Sustained Energy

Food quality matters as much as quantity. Select carbohydrate sources that provide sustained energy, essential nutrients, and optimal digestive tolerance. Let’s dive even deeper into simple vs complex carbs.

A container of EndurElite Carb Elite sits on the muddy rear tire of a mountain bike outdoors.

High-Quality Complex Carbohydrates

Focus on whole food sources like old-fashioned oats, brown rice, barley, and millet. These options contain fiber, which helps stabilize blood sugar levels during long training sessions.

Global grains such as quinoa and bulgur add nutritional diversity. They provide complete amino acid profiles along with their carbohydrate content.

For convenience, you can even use cluster dextrin, which is technically a complex carbohydrate, but its unique structure allows it to be digested and absorbed quickly, providing a steady release of energy. EndurElite Carb Elite contains cluster dextrin, which I recommend to all my athletes.

Fill your plate with fruits, sweet potatoes, peas, legumes, and non-starchy vegetables. Most of these have a glycemic index of 55 or below. This means they cause only gradual increases in blood glucose rather than sharp spikes.

The American Heart Association recommends choosing whole-grain pasta or bread over refined white flour products. This simple swap increases your intake of vitamins, minerals, and heart-protective nutrients.

Simple Carbs for Training Windows

Reserve simple, refined sugars or processed snacks for specific training applications. Use them during events when you need rapid energy delivery.

Bananas, raisins, and honey packets travel well for mid-competition fuel. These whole food sources provide quick glucose without artificial additives. You can also use something like EndurElite Fuel Elite.

Skip sugar substitutes like sucralose or Splenda during training. These nonnutritive sweeteners provide no fuel and may disrupt gut bacteria that support performance.

Conclusion

Simple vs complex carbs shouldn’t be an either/or. It’s more about timing them appropriately for training and competition. The goal should be lasting performance.

Use simple carbs like dextrose for quick energy immediately before or during long workouts. Focus on complex carbs to maintain steady energy release.

For the best results possible, combine whole foods with supplements, like those from EndurElite that are designed specifically for endurance athletes pursuing peak performance at every distance.

FAQs

Are simple carbs always bad for endurance athletes?

No, simple carbs are beneficial before or during workouts when fast energy is needed.

How do complex carbs help with endurance?

They provide slow, consistent energy that supports longer training sessions and reduces fatigue.

What’s the best pre-race meal for endurance athletes?

A balanced meal rich in complex carbs like oatmeal or rice, paired with lean protein and limited fat.

Why choose EndurElite for endurance nutrition?

EndurElite’s clean, transparent formulas support optimal energy metabolism, muscle recovery, and endurance performance.