Are Simple or Complex Carbs Good for Carb Loading?

December 15, 2025 •

4 min read

Athletes can store enough carbohydrates to fuel approximately 90 minutes of high-intensity exercise. Therefore, understanding whether simple or complex carbs are good for carb loading is key to endurance. The answer involves strategic timing and the specific type of carbohydrate to maximize muscle glycogen stores.

Quick Summary

This article discusses simple versus complex carbohydrates in the context of carb loading. It details the best timing for each type to optimize glycogen stores, providing a strategic look at how to structure carbohydrate intake before an endurance event.

Key Points

Complex Carbs for Main Loading: Prioritize complex, low-fiber carbohydrates in the 36-48 hours before an event to build up muscle glycogen stores steadily.
Simple Carbs for Immediate Energy: Use simple carbohydrates in the final hour before and during the race for a rapid, on-demand fuel source.
Reduce Fiber Before Race: Lowering fiber intake from complex carbs in the days leading up to the event helps prevent gastrointestinal distress on race day.
Timing is Everything: The key difference lies in the timing—complex carbs for long-term storage, simple carbs for immediate bursts.
Hydration is Crucial: Remember to increase your fluid intake alongside your carbohydrate consumption during the loading phase, as carbs store water.
Practice the Strategy: Always test your carb-loading plan during training to ensure your body responds well to your chosen foods and quantities.

The Science of Carb Loading: Maximizing Glycogen Stores

Carbohydrate loading is a dietary approach used by endurance athletes to increase the storage of glycogen in their muscles and liver. Glycogen is the body's primary fuel for high-intensity, prolonged exercise. When these stores are maximized, athletes can sustain their performance and delay fatigue. While carbohydrates serve this purpose, the type of carb—simple or complex—plays a distinct role depending on the timing relative to the event.

Complex Carbs: The Foundation of Carb Loading

For the main phase of your carb-loading strategy, which typically occurs 36-48 hours before an endurance event, complex carbohydrates are the primary choice. Complex carbs are made of longer chains of sugar molecules, and they take longer for the body to break down and digest. This provides a slow, sustained release of glucose into the bloodstream, which is ideal for steadily building up glycogen reserves without causing drastic blood sugar spikes and crashes. Foods rich in complex carbs include:

White rice and white pasta
Potatoes (without high-fiber skins)
Oats
White bread and bagels
Certain low-fiber cereals

It is important to note that many complex carb sources, like whole grains and fibrous vegetables, are high in dietary fiber. While fiber is crucial for general health, reducing intake in the final days before a race can prevent gastrointestinal (GI) distress during the event. This is why many athletes opt for refined, lower-fiber versions of complex carbohydrates, such as white pasta over whole-wheat pasta.

Simple Carbs: The Final Push and Race Fuel

Simple carbohydrates, composed of one or two sugar molecules, are digested very quickly, providing a rapid boost of energy. During the final hours before a competition, and particularly during the event itself, simple carbs are beneficial. They are rapidly absorbed to provide immediate fuel, helping to top off glycogen stores and provide energy during the race. However, relying solely on simple sugars too far out from an event can lead to energy crashes and sluggishness.

Strategically, simple carbs are most effective:

Immediately pre-race (30-60 minutes before): A small snack like an energy gel, a banana, or some sports chews can provide a quick, last-minute energy burst.
During the event: Energy gels, sports drinks, and easy-to-digest sugary treats are used to continuously replenish glycogen as it's burned.

Comparing Simple vs. Complex Carbs for Carb Loading


Feature	Complex Carbohydrates	Simple Carbohydrates
Digestion Speed	Slow and sustained.	Fast and rapid.
Energy Release	Steady and prolonged, avoiding crashes.	Quick burst of energy, can lead to energy spikes and crashes.
Nutrient Density	Often higher in vitamins and minerals (but lower-fiber options are preferred for loading).	Lower in micronutrients, often called "empty calories" outside of fruit.
Typical Timing	36-48 hours before the event.	Last hour before the event and during the event.
Ideal for	Maximizing long-term glycogen storage leading up to the race.	Providing immediate, on-demand energy during exercise.
Fiber Content	Can be high (reduce for loading).	Low, minimizing GI distress.

How to Structure Your Carb Loading Strategy

A successful carb-loading plan uses a combination of both carbohydrate types at the optimal time. The general recommendation for endurance events is to increase carbohydrate intake to 8-12 grams per kilogram of body weight per day in the 24-48 hours leading up to the event.

Step 1: 36-48 Hours Before the Race

Focus on consuming complex, low-fiber carbohydrates. This is the main phase for filling your glycogen reserves. For a 70kg athlete, this could mean aiming for 560-840 grams of carbs per day. Meals should be centered around easily digestible sources like pasta, rice, and potatoes.

Step 2: The Night Before the Race

Keep it simple and familiar. A dinner rich in complex carbs, such as a pasta dish with a light, low-fiber sauce, is a common choice. Avoid overly spicy, fatty, or high-fiber meals that could upset your stomach.

Step 3: The Morning of the Race

About 3-4 hours before the event, have a breakfast rich in easily digestible carbs. Oatmeal or a bagel are excellent choices. For the final hour, a small amount of simple carbohydrates, like a banana or energy chews, can give you a final energy top-off without weighing you down.

Step 4: During the Race

During the event, your body needs a constant supply of quick-absorbing fuel. This is where simple carbs excel. Consume energy gels, sports drinks, or chews to maintain blood sugar levels and spare muscle glycogen stores, delaying fatigue.

Conclusion: Strategic Use is Key

So, are simple or complex carbs good for carb loading? Both are, but their effectiveness depends on strategic timing. Complex carbs are the workhorses for building up long-term glycogen stores in the days before an event, while simple carbs provide the quick, on-demand fuel needed immediately before and during intense exercise. By combining both types of carbs with a reduced training volume and adequate hydration, athletes can create a powerful nutritional strategy to optimize performance and reach their endurance goals.

Final Recommendations for Athletes

To nail your carb-loading strategy, remember these key points:

Practice your plan during training to see what works for your body and avoid race-day surprises.
Prioritize complex, low-fiber carbs in the 36-48 hours leading up to the event.
Reserve simple carbs for the final hour before and during the race for quick energy.
Hydrate consistently throughout the carb-loading period and during the race.
Experiment with different foods and quantities to find your personal optimal intake.

For more detailed sports nutrition advice, consulting an expert is always recommended. A great resource for general health guidance is the Cleveland Clinic, which provides thorough information on macronutrients and balanced diets.

For more information on nutrition, see this article about macronutrients on the Cleveland Clinic website.

Frequently Asked Questions

Yes, a pasta dinner with a light, low-fat, low-fiber sauce is an excellent choice for the evening before an event. However, it is a common mistake to rely solely on this one meal. Effective carb loading starts 36-48 hours in advance, so the night-before meal is simply part of a larger strategy.

For carb loading, it is generally better to opt for refined, low-fiber grains like white rice and white pasta over whole grains. The high fiber content in whole grains can cause digestive issues during a race, which is a major concern for endurance athletes.

No, older methods that involved a carb depletion phase are no longer considered necessary for trained athletes. Modern carb-loading strategies show that moving straight from a standard diet to a high-carb one 24-48 hours before the event is sufficient and less stressful on the body.

Yes, most sports drinks and energy gels are designed with simple carbohydrates (like maltodextrin or fructose) for rapid absorption. They are excellent sources of immediate fuel during an endurance event.

Recommendations typically range from 8 to 12 grams of carbohydrates per kilogram of body weight per day during the carb-loading phase, depending on the event and the athlete's body. For example, a 70kg athlete would aim for 560-840 grams daily.

Some athletes may experience mild bloating, especially when consuming a high volume of carbohydrates. To minimize this, focus on easily digestible, lower-fiber carbs and spread your intake evenly throughout the day. Drinking your carbs via sports drinks can also help.

Carb loading is generally not necessary for races shorter than 90 minutes, such as a 5K. The body's normal glycogen stores are sufficient for these shorter events. Focusing on a well-balanced diet and proper hydration is more important.

If consuming enough solid food becomes a challenge, particularly for those with a smaller appetite, incorporating simple carb drinks like sports drinks or fruit juices can be an effective strategy to increase overall carbohydrate intake without excess bulk.