Fueling for the Win: What is the Ideal Carb Load?

October 7, 2025 •

4 min read

Effective carb loading has been shown to improve endurance performance by 2-3% in events lasting longer than 90 minutes. To achieve this edge, athletes need to understand precisely what is the ideal carb load and how to execute it effectively without feeling sluggish or bloated on race day.

Quick Summary

Carb loading is a proven strategy for endurance athletes to maximize muscle and liver glycogen stores before a long-duration event. It requires calculating personal carbohydrate needs based on body weight and strategically adjusting diet and exercise in the final days before a race.

Key Points

Calculate by Weight: Use the guideline of 8-12 grams of carbs per kilogram of body weight to determine your daily intake for carb loading.
Start 24-48 Hours Early: Begin increasing your carbohydrate intake and reducing training volume in the one to two days leading up to your event.
Choose Low-Fiber Carbs: Opt for easily digestible options like white pasta, rice, and potatoes to prevent gastrointestinal distress on race day.
Hydrate Well: Drink plenty of fluids during the carb-loading period, as glycogen binds with water in the muscles.
Practice Your Plan: Always test your carb-loading strategy during your long training runs to know how your body will react on race day.
Don't Overeat Fat or Fiber: Reduce fat and fiber intake during the final days to leave room for more carbohydrates and aid digestion.
Avoid the Depletion Phase: Forget the outdated practice of depleting your glycogen stores before loading; modern approaches are more effective and less taxing.

Understanding the Science of Carb Loading

Carb loading, or carbohydrate loading, is a strategic dietary approach used by endurance athletes to maximize the amount of glycogen stored in their muscles and liver. Glycogen is the body's primary fuel source during high-intensity and prolonged exercise. Our bodies can typically store enough glycogen to fuel about 90 minutes of intense activity. For events lasting longer, such as a marathon, long-distance cycling race, or triathlon, these stores become depleted, a phenomenon known as "hitting the wall". By super-saturating the body's glycogen reserves in the days leading up to an event, athletes can delay fatigue and maintain peak performance for longer periods.

Calculating Your Ideal Carb Load

Determining your specific carb-loading needs is based on your body weight and the event's duration and intensity. For endurance events lasting over 90 minutes, the general recommendation for carbohydrate intake is between 8 and 12 grams per kilogram (kg) of body weight per day. This needs to happen over a period of one to three days, typically in conjunction with a reduced training load, or taper, to ensure maximum storage.

Let's put this into perspective. For a 70kg (approx. 154 lbs) athlete, the target intake would be between 560 and 840 grams of carbohydrates per day. Spreading this intake across multiple meals and snacks, and potentially using liquid carbohydrates, is often necessary to comfortably consume such a large quantity.

The Carb Loading Timeline

Modern carb-loading protocols have simplified the process significantly, moving away from the outdated "depletion phase" that involved intense exercise and low-carb dieting. Here's a typical modern timeline:

36 to 48 Hours Before the Event: This is the key window for increasing carbohydrate intake to the recommended 8-12 g/kg/day range. Simultaneously, reduce your training volume to a minimal level to ensure the carbohydrates are stored as glycogen instead of being burned for fuel.
The Day Before the Event: Focus on easily digestible, low-fiber, carb-rich foods to avoid gastrointestinal issues on race day. Reduce fat and protein intake to make room for more carbohydrates.
Race Day Morning: Consume a carb-rich breakfast 2-4 hours before the start. This meal replenishes liver glycogen stores, which can be depleted overnight. Stick with foods you've practiced with during training.

The Best Foods for Carb Loading

Choosing the right foods is crucial for effective carb loading and avoiding digestive discomfort. The goal is to consume high-carb, low-fiber options that are easy on the stomach. Here are some examples:

White Rice and Pasta: Simple, low-fiber versions are easily digestible and calorie-dense.
Potatoes: Mashed or baked potatoes without the skin are excellent choices.
White Bread and Bagels: These provide a quick and easy source of carbohydrates.
Oats: Quick-cooking or rolled oats can be good, but monitor how the fiber affects you.
Fruits: Bananas are a great, low-fiber option. Be mindful of higher-fiber fruits.
Sports Drinks and Juices: Liquid carbohydrates are an easy way to meet high intake goals, especially when solid food feels too bulky.
Energy Gels and Chews: Can be used to supplement intake, especially for a final top-up.

What to Avoid During Carb Loading

Excessive Fiber: Foods like whole grains, beans, and high-fiber vegetables can cause bloating, gas, and digestive upset.
High-Fat Foods: Fats slow digestion and can make you feel full too quickly, preventing you from consuming enough carbohydrates.
New or Unfamiliar Foods: Sticking to a tested and proven diet is key to avoiding race-day surprises.
Overeating: Carb loading is about adjusting macronutrient ratios, not just increasing total calories. While you might feel full, aim for frequent, moderate portions.

Practice Makes Perfect

Just like training your muscles, you need to train your gut. Always test your carb-loading plan during long training sessions before using it for a major race. This helps you identify which foods and timing strategies work best for your body, minimizing the risk of GI issues on the big day.

Comparison of Carb Loading Strategies


Strategy	Timeline	Recommended Carb Intake	Key Features	Best For
Modern High-Carb	24-48 hours before event	8-12 g/kg of body weight per day	High-carb, low-fiber diet with reduced training.	Most endurance athletes competing for >90 minutes.
Classic Depletion	6 days total (depletion + loading)	~5 g/kg carbs, then 10-12 g/kg carbs	Low-carb diet with intense exercise, followed by high-carb diet with rest.	Outdated, often leads to fatigue and distress.
Single-Meal Load	1 big meal the night before	Not effective for maximizing stores	Relies on one meal to do the work of several days.	Not recommended for endurance events.
No Carb Load	N/A	Normal diet	Standard eating patterns without adjustment.	Events under 90 minutes; no performance boost.

Conclusion: Your Ideal Carb Load is a Personal Strategy

Determining what is the ideal carb load is not a one-size-fits-all solution but a calculated and practiced strategy. By focusing on your body weight, event duration, and choosing the right easily digestible foods, you can effectively maximize your glycogen stores. Remember to practice your strategy well in advance of a competition to fine-tune it for your individual needs. By doing so, you can ensure you show up at the starting line fully fueled and ready to perform at your best, avoiding the dreaded energy crash.

For more detailed sports nutrition guidelines, consult resources from reputable organizations such as the Sports Dietitians Australia.

Frequently Asked Questions

The main purpose of carb loading is to maximize the amount of glycogen stored in your muscles and liver. This increases your energy reserves, delaying fatigue during long-duration endurance events.

Carb loading is most beneficial for endurance athletes competing in events lasting 90 minutes or longer, such as marathons, triathlons, and long-distance cycling. It is not necessary for shorter events or for general, less intense workouts.

A modern carb-loading protocol typically takes place over 24 to 48 hours leading up to the race. This window is sufficient for maximizing your glycogen stores without the need for longer, multi-day strategies.

During carb loading, focus on low-fiber, high-carbohydrate foods that are easy to digest. Good options include white rice, pasta, bread, potatoes, sports drinks, and fruit juices. Avoid high-fat and high-fiber foods.

During carb loading, for every gram of glycogen stored, your body also stores extra water. This can lead to a temporary weight gain of 1-2 kilograms and a feeling of being a little heavier, which is a normal and beneficial part of the process.

Yes, you should still include some protein and healthy fats, but in smaller quantities. During the carb-loading phase, carbohydrates should make up the majority of your caloric intake to prioritize glycogen storage.

While a pasta dinner is a classic pre-race meal, relying on a single, oversized meal is not recommended. It can cause digestive distress and is not enough to maximize glycogen stores. It's more effective to spread your carb intake across smaller, frequent meals and snacks over the 24-48 hours prior.