Fiber for Runners: Benefits, Best Practices, and Race Day Tips

Fiber is a crucial part of a healthy diet, but for runners, it can be a double-edged sword. While it supports digestion and overall well-being, consuming too much at the wrong time—especially before a run—can cause stomach discomfort and unexpected pit stops. How do you strike the right balance? Here’s everything you need to know about fiber intake for runners, including how to adjust it around races.

Why Is Fiber Important for Runners?

Fiber is a type of carbohydrate—specifically a polysaccharide (cellulose)—that the body doesn’t fully digest. It comes in two forms:

• Insoluble fiber: Speeds up digestion by adding bulk to stool.
• Soluble fiber: Dissolves in water and ferments in the gut, supporting gut bacteria and digestion.

A fiber-rich diet is linked to better heart health, lower cancer risk, improved blood sugar control, and digestive health.

For runners, fiber helps maintain regular digestion, ensuring proper nutrient absorption and reducing the risk of constipation.

Additionally, fiber-rich carbohydrates—such as whole grains, fruits, and vegetables—are packed with micronutrients that support training. Unlike simple carbs, they provide sustained energy and keep you feeling full longer.

How Much Fiber Should Runners Eat?

The recommended fiber intake for runners is 20 to 35 grams per day, depending on overall calorie needs.

You can meet this target by eating:

• Vegetables (spinach, carrots, peppers)
• Fruits (berries, apples, oranges)
• Whole grains (brown rice, oats, whole wheat bread)
• Legumes (beans, lentils, chickpeas)
• Seeds and nuts (chia, flaxseeds, almonds)

However, more fiber is not always better. Exceeding 35 grams per day may cause:

• Gastrointestinal distress (bloating, gas, stomach cramps)
• Frequent bathroom trips during runs
• Reduced calorie intake due to feeling too full

Adjusting Fiber Intake Before a Race

While fiber is beneficial for long-term health, consuming it too close to a run or race can lead to GI distress.

Since fiber slows digestion and draws more water into the intestines, it may cause bloating, gas, or urgency to use the bathroom while running.

A 2018 study in Medicine and Science in Sports and Exercise found that runners who reduced fiber intake before a race (specifically FODMAPs, high-fiber foods that ferment in the gut) experienced fewer digestive issues.

To minimize the risk of GI problems on race day:

• Reduce fiber intake the day before the race, especially gas-producing foods like legumes and cruciferous vegetables (broccoli, cauliflower, Brussels sprouts).
• Stick to low-fiber carbohydrates for breakfast before the race.
• If you have a history of GI issues, start lowering fiber two days before the race.
• Avoid increasing fiber intake during carb loading before a race.

If eating within two hours of a run, opt for low-fiber foods since fiber takes about two hours to digest.

Best Low-Fiber Foods for Runners

Before a run or race, choose easy-to-digest, low-fiber carbohydrate sources to prevent stomach discomfort:

• White bread/bagel
• Graham crackers
• Fruit juice
• Pretzels
• White rice
• Fig bars or breakfast bars
• Applesauce
• Low-fiber cereals

For the day before a race, make these low-fiber substitutions we recommend to eat some carb-rich foods.

Why Fiber Timing Matters for Runners

Fiber delays digestion and increases stool bulk, which is great for gut health but not ideal before intense exercise. While fiber helps promote regularity, excessive fiber right before a run can lead to:

• Bloating and stomach cramps
• Frequent bathroom breaks
• Reduced carbohydrate availability, impacting performance

That’s why fiber-rich meals are best consumed after running, rather than before.

Final Thoughts: How Runners Should Approach Fiber

Fiber is an essential part of a balanced diet, and runners should not avoid it completely. Most of the time, it’s best to choose fiber-rich foods for their health benefits and nutrient density. However, adjusting fiber intake before runs and races can prevent digestive discomfort.

Key Takeaways:

- Fiber supports digestion and overall health but can cause issues if consumed too close to running.
- Daily fiber intake for runners should be 20-35 grams, mainly from whole foods like vegetables, fruits, whole grains, and legumes.
- Reduce fiber before races and key workouts to avoid stomach issues.
- Eat low-fiber carbs before runs to ensure smooth digestion.

By managing fiber intake wisely, you can support both your training and digestive health, ensuring a strong performance on race day.