Why a long distance runner requires carbohydrates and fats in their diet

December 15, 2025 •

3 min read

Endurance athletes who follow a high-carbohydrate diet have been shown to run faster and longer in races lasting over 45 minutes. This is just one of many reasons why a long distance runner requires carbohydrates and fats in their diet to maximize performance, endurance, and overall health.

Quick Summary

Long-distance runners need a balanced intake of carbohydrates and fats to optimize performance, manage energy, and aid recovery. Carbohydrates provide quick energy, while fats offer a dense, sustained fuel source for endurance. These macronutrients are crucial for supporting the physiological demands of prolonged exercise.

Key Points

Carbohydrates are the primary fuel for high-intensity running: Stored as glycogen, they offer the quick energy needed for faster paces and intense efforts, delaying fatigue.
Fats are the power source for endurance: Providing a dense, sustained fuel supply, fats are primarily used during lower-intensity, longer runs, helping to preserve precious carbohydrate stores.
Timing your fuel intake is critical: Strategically consuming carbohydrates before, during, and after runs, while focusing on healthy fats daily, optimizes energy availability and recovery.
The body adapts to burn fat more efficiently with training: Consistent endurance training enhances the body's metabolic machinery, improving its ability to use fat as an energy source.
A balanced diet ensures sustained performance and health: Relying on both carbohydrates and fats, alongside protein and micronutrients, is essential for a runner's overall health, injury prevention, and peak athletic performance.

The Dual Fuel System: Why Runners Need Both Carbs and Fats

For a long-distance runner, the body utilizes both carbohydrates and fats for energy. Carbohydrates offer quick fuel for intense running, while fats provide a sustained energy source for longer efforts. Efficiently using both is essential for maintaining performance and preventing fatigue.

The Role of Carbohydrates: The High-Intensity Fuel

Carbohydrates are the body's preferred energy source for high-intensity exercise. They are converted to glucose and stored as glycogen in muscles and the liver.

Quick Energy: Glycogen is readily available to produce ATP, enabling higher intensity running.
Glycogen Sparing: Consuming carbohydrates during exercise helps preserve muscle glycogen, delaying fatigue and allowing a faster pace for longer.
Cognitive Function: Glucose powers the brain, preventing mental fatigue during long efforts.
Recovery: Post-exercise carbohydrate intake is crucial for replenishing glycogen stores, supporting muscle repair and preparing for future training. A 3:1 carb-to-protein ratio is often recommended for recovery.

The Importance of Fats: The Endurance Engine

Fats are vital for endurance, providing a concentrated, sustained energy source (9 calories per gram). They are the primary fuel during lower-intensity, longer runs, conserving precious glycogen.

Long-Lasting Energy: Fats offer a dense and sustained energy source for prolonged exercise.
Hormone Production and Absorption: Healthy fats support hormone production and the absorption of fat-soluble vitamins (A, D, E, K), important for immune and bone health.
Inflammation Reduction: Omega-3 fatty acids in unsaturated fats can help reduce muscle soreness and aid recovery.
Increased Fat Oxidation: Endurance training improves the body's efficiency in using fat for fuel, reducing reliance on carbohydrate stores during longer efforts.

Strategic Timing for Optimal Performance

Proper timing of carbohydrate and fat intake is key for smart fueling.

Daily Diet: Aim for 55-65% of daily calories from carbohydrates and 20-35% from healthy fats to build glycogen stores and support overall health.
Pre-Run Fuel: Consume easily digestible carbohydrates 1-4 hours before a run to top off glycogen. Avoid high-fat meals pre-run due to slow digestion.
During Long Runs: For runs over an hour, consume 30-90 grams of carbohydrates per hour to maintain blood glucose and spare glycogen.
Post-Run Recovery: Replenish glycogen with carbohydrates and protein immediately after a run to aid muscle repair.

Carbohydrates vs. Fats for Long-Distance Running


Feature	Carbohydrates	Fats
Energy Source	Primary fuel for high-intensity exercise	Primary fuel for low-to-moderate intensity exercise and recovery
Energy Density	~4 calories per gram	~9 calories per gram
Energy Release Rate	Fast; readily available	Slow; sustained release
Body Storage	Limited (glycogen)	Vast (adipose tissue)
Metabolic Efficiency	More efficient, uses less oxygen for same energy	Less efficient, uses more oxygen for same energy
Best for...	Maintaining speed and avoiding the 'bonk'	Sustaining prolonged, sub-maximal effort
Timing for Consumption	Before, during, and after runs	Daily intake; avoid immediately pre-run

Conclusion: A Synergistic Approach

A long-distance runner's diet requires both carbohydrates and healthy fats. Carbohydrates provide quick energy for intense efforts and recovery, while fats offer dense, long-term fuel for endurance. Managing the intake and timing of these macronutrients fuels the body, delays fatigue, and supports a strong finish. A balanced nutrition plan utilizing both fuels is crucial for peak performance and a competitive edge.

Frequently Asked Questions

A low-carb diet is generally not recommended for long-distance runners because carbohydrates are the most efficient fuel for high-intensity efforts. Significantly reducing carbohydrate intake can impair performance, reduce muscle glycogen stores, and hinder recovery.

When a runner's carbohydrate stores (glycogen) are depleted, they experience a phenomenon known as 'hitting the wall' or 'bonking.' This results in profound fatigue, a significant drop in pace, and potential mental fog.

For runs lasting over 60 minutes, a runner should aim to consume 30-90 grams of carbohydrates per hour. This helps maintain stable blood sugar levels and spares muscle glycogen.

Runners should prioritize healthy, unsaturated fats such as monounsaturated and polyunsaturated fatty acids. Good sources include avocados, nuts, seeds, and fatty fish.

Healthy fats, particularly omega-3s, have anti-inflammatory properties that can help reduce muscle soreness and inflammation after a tough run, aiding in the recovery process.

Fats are more energy dense, providing approximately 9 calories per gram compared to the 4 calories per gram from carbohydrates and protein.

Yes, regular endurance training increases mitochondrial density and upregulates fat-metabolizing enzymes, improving the body's ability to use fat as an energy source.