How Many Grams of Carbohydrates for an Athlete During a Prolonged 3-Hour Event?

November 18, 2025 •

4 min read

Research consistently shows that inadequate carbohydrate intake during prolonged exercise can significantly reduce performance by as much as 30-40%. Understanding how many grams of carbohydrates are needed is crucial for any athlete competing in or training for a prolonged 3-hour event. This guide will detail the science-backed recommendations for optimal fueling and performance.

Quick Summary

Optimal carbohydrate intake during a 3-hour endurance event ranges from 60 to 90 grams per hour. Consuming multiple transportable carbohydrates, like glucose and fructose, improves absorption. Proper fueling and 'gut training' are vital to minimize gastrointestinal issues and sustain performance.

Key Points

60–90 Grams Per Hour: For endurance events lasting 2.5 to 3 hours, a target intake of 60 to 90 grams of carbohydrates hourly is recommended to maximize performance.
Multiple Transportable Carbs: To exceed 60 grams per hour, use products containing a mix of glucose and fructose. This utilizes different absorption pathways, allowing for higher intake without stomach distress.
Practice 'Gut Training': Your digestive system needs practice. Regularly consuming your race-day nutrition strategy during training will improve tolerance and minimize the risk of gastrointestinal issues.
Balance Fuel and Fluids: Your fueling plan should be balanced with a hydration strategy. Highly concentrated carbohydrate sources can slow fluid absorption, so integrate electrolyte sports drinks for optimal intake.
Personalize Your Plan: Individual needs and tolerances differ. Use the 60-90 g/h recommendation as a starting point, but test different products and amounts in training to find what works best for your body.

The Science Behind Mid-Event Carbohydrate Intake

For endurance events lasting over 90 minutes, such as a 3-hour race, carbohydrate consumption becomes critical for sustaining performance and preventing the dreaded 'bonk'. The body's natural glycogen stores are typically sufficient for about 60 to 90 minutes of high-intensity exercise. After this, exogenous (external) carbohydrates are needed to maintain blood glucose levels and fuel the working muscles.

Why 60–90 Grams Per Hour?

For events extending beyond two hours, the recommended carbohydrate intake increases from the standard 30–60 grams to a higher 60–90 grams per hour. This higher intake rate is primarily due to the intestinal absorption limitations of a single carbohydrate source, like glucose. Glucose is absorbed via a specific transporter, SGLT1, which can become saturated at an intake of around 60 g/h.

To overcome this limitation, combining different types of carbohydrates that use separate transporters is essential for higher intake rates. Multiple transportable carbohydrates, most notably a glucose-to-fructose ratio, allow for greater absorption and energy availability. Fructose is absorbed through the GLUT5 transporter, effectively creating a second pathway for carbohydrate entry into the body's system. For events exceeding 2.5 hours, using a multiple carbohydrate source is recommended for ingesting over 60 grams per hour.

The Importance of 'Gut Training'

The ability to tolerate and absorb high carbohydrate loads during exercise is not innate; it is a skill that can be developed through 'gut training'. Just as you train your muscles, you must train your digestive system to handle the increased intake of energy gels, drinks, and chews without causing gastrointestinal distress. Consistent practice with your planned race-day nutrition strategy during training will help reduce the risk of stomach problems. Starting with lower amounts and gradually increasing intake during longer training sessions is a proven method for improving gut tolerance.

Fueling Strategy for a 3-Hour Event

Planning a nutrition strategy for a prolonged event is essential. It requires not only knowing the target intake but also practicing how to achieve it through consistent, timed feeding.

A Sample Fueling Plan

Pre-Event: A carbohydrate-rich meal (1-4 g/kg of body weight) consumed 1 to 4 hours before the event to top off glycogen stores.
During: Consume 60–90 grams of carbohydrates per hour, beginning within the first hour of the event. This can be broken down into smaller, more frequent doses (e.g., 20-30 grams every 20-30 minutes) to manage blood sugar and prevent stomach upset.
Post-Event: Immediately after the event, consume 1.0–1.2 g/kg of high glycemic index carbohydrates within the first four hours to kickstart glycogen resynthesis.

A Comparison of Common Fuel Sources


Fuel Source	Carbohydrate Content	Glucose:Fructose Ratio	Considerations
Energy Gel	~20–30g per gel	Varies (often 2:1)	Convenient, fast-acting. Should be consumed with water. May cause palate fatigue.
Energy Chews	~20–30g per serving	Varies	Solid food alternative. Easy to carry and portion. Requires chewing.
Sports Drink	~60g per liter	Varies (often 2:1)	Provides hydration and electrolytes along with carbs. A 6-8% concentration is optimal.
Energy Bar	~40–60g per bar	Varies	Provides solid food feel. Choose low-fat, low-fiber options to avoid digestive issues.
Dried Fruit (e.g., raisins)	~20g per 1/4 cup	Natural	Provides natural sugars but can be higher in fiber, potentially causing GI issues.

A Sample 3-Hour Fueling Plan

Hour 1: 1 Energy Gel (25g) + 500ml Sports Drink (30g) = 55g Total. Start with the sports drink early and take the gel at the 30-minute mark.
Hour 2: 1 Energy Bar (45g) + 500ml Sports Drink (30g) = 75g Total. Consume the bar in smaller bites throughout the hour, accompanied by consistent sips of your sports drink.
Hour 3: 2 Energy Gels (50g) + 500ml Sports Drink (30g) = 80g Total. Use gels for rapid energy as fatigue sets in during the final hour.

This is just an example; your actual needs will depend on factors like body weight, intensity, and personal tolerance. It is crucial to experiment with different products and quantities during training to find a strategy that works best for you.

Hydration and Electrolytes

Alongside your carbohydrate intake, maintaining hydration is vital. Sports drinks containing electrolytes, particularly sodium, can help replace what is lost through sweat. In high temperatures, sweat rates increase, and electrolyte losses become more significant. An effective fueling plan incorporates both carbohydrate and fluid intake, as highly concentrated carbohydrate solutions can slow gastric emptying and absorption.

Conclusion

Fueling a prolonged 3-hour athletic event requires a strategic and practiced approach. The science supports consuming 60 to 90 grams of carbohydrates per hour, using multiple transportable carbohydrate sources to maximize absorption and energy availability. Developing gut tolerance through training is a non-negotiable step to prevent gastrointestinal issues on race day. By planning your intake, practicing with your chosen fuel sources, and staying adequately hydrated, you can effectively manage your energy levels and sustain your performance throughout the entire event. Remember that individual needs vary, and what works for one athlete may not work for another, so testing and personalization are key to success.

Frequently Asked Questions

The body's primary glucose transporter, SGLT1, becomes saturated at around 60 grams per hour. To absorb more, you need a different carbohydrate like fructose, which uses a different transporter (GLUT5), enabling higher intake rates.

'Gut training' is the practice of repeatedly consuming your race-day fueling strategy during training sessions. This helps your digestive system adapt to and tolerate higher carbohydrate intake rates without causing gastrointestinal issues like bloating or nausea.

You can use a combination of sports drinks, energy gels, chews, and bars. For example, a sports drink providing 30g/hour paired with one or two energy gels or chews can help you reach your target intake.

No, recommendations for carbohydrate intake during exercise are not typically based on body weight because the limiting factor is the gut's absorption capacity, which is largely independent of weight.

You should start your fueling strategy early in the event, ideally within the first 30 minutes, to ensure a steady supply of energy and prevent glycogen depletion.

If you experience discomfort, you may be consuming too much too quickly or using a source your gut isn't adapted to. Slow your intake, use multiple transportable carbohydrates, and practice 'gut training' to improve tolerance.

This depends on personal preference and how your body reacts. Gels and drinks provide rapid energy, while solid foods like low-fiber bars can feel more substantial. Many athletes use a mix-and-match approach.