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If you’ve heard of fiber, you’ve probably heard that it’s a nutrient that fills you up—and sends you to the bathroom. But what you might not know is that most Americans (runners included!) don’t get enough fiber in their diets. That’s a problem not only for your gut, but for your overall health and performance.
We spoke to two registered dietitians and dug into the research to find out exactly what is fiber, why it’s so important, and how runners can incorporate high-fiber foods into their diets without disrupting their training.
What is fiber?
All the yummy, energizing fruits and veggies that we love contain carbohydrates, and fiber is one of them. Fiber is a type of carbohydrate that plays a role in maintaining overall health, and it comes in three different forms—soluble, insoluble, and functional. Each type plays a different role in keeping you healthy.
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“Soluble fiber is the type that dissolves in liquid and that includes the liquid in our stomach and our gastrointestinal tract,” Kelly Jones M.S., R.D., C.S.S.D., sports dietitian and professor of nutrition and exercise at Bucks County Community College tells Runner’s world. When soluble fibers dissolve, it forms a gel-like texture that helps your body absorb other nutrients and slows down digestion, she says.
Insoluble fibers are the opposite. Kristin Kabay, M.S., R.D., C.S.S.D., sports dietitian and marathon runner explains, “they’re not dissolved in water. They kind of act like a broom—combing through your intestines, and just sweeping everything out.” This type of fiber is the one that clears your body of toxins, regulates bowel movements, and prevents constipation.
Lastly, functional fibers are supplements added into packaged foods by manufactures, likely to help some people kick up their fiber intake, Kabay says. You can spot some of these additive ingredients—like soluble corn fiber or enriched wheat flour—on the nutrition label of some packaged foods.
Eating foods overloaded with functional fiber, especially if you have a sensitive digestive tract, can cause constipation or bloating, says Jones. “If you’re seeing that one type of fiber was added to a product, and you’re not seeing other whole plant foods on your ingredient list, then you know that that might be an overload of the type of fiber that can impact your digestive health,” she adds.
Luckily, fruits and veggies are rich in soluble and insoluble fibers, Kabay says, so you don’t have to track how much of each fiber you eat.
Why is fiber so important?
Eating the right amount of fiber each day—31 grams for men and 25 grams for women according to the USDA—can yield a ton of different health benefits. The number-one reason fiber is so important, Kabay says, is because it can be incredibly beneficial to lots of different organ systems through the body, including your gut and heart.
Research backs up fiber’s many benefits. For starters, a recent study published in the journal American Society for Microbiology found an association between a high-fiber diet and fewer antibiotic-resistant microbes in the gut. This shows that fiber may help fight antibiotic resistance which is what prevents bacteria, viruses, and fungi from effectively responding to antibiotics.
In terms of heart health, a recent prospective study published in the journal Nutrients found eating natural sources of dietary fiber, such as legumes, fruits, vegetables, and nuts had a protective effect against cardiovascular disease. Plus, a meta-analysis published in the Journal of Diabetes Investigation associated a higher intake of fiber with lower risk for type 2 diabetes with an emphasis on the protective effects of berries, green leafy vegetables, yellow vegetables, and cruciferous vegetables.
What’s more, Kabay says upping your intake of fiber can help lower cholesterol and blood sugar levels, as well as decrease your risk for colon cancer. Also, Jones points to research that shows increasing your fiber intake can improve your mental health.
What happens if you don’t get enough fiber?
If you don’t eat enough fiber in your diet, Jones says, you may experience the following symptoms:
- Irregular bowel movements
- Constipation and digestive distress
- Poor gut health, which can impact immune function, metabolism, and even mental health
- High blood cholesterol
- Fluctuations in blood sugar levels
- Lack of satiety after eating
How to include more fiber in your diet
While it may seem like adding a bunch of high-fiber foods to your diet at once would be the easiest way to approach increasing your fiber intake, it probably isn’t the smartest.
Jones says eating too much fiber at one time can cause digestive issues. To avoid this, gradually increase the amount of fiber you eat each day and focus on eating the fruits and vegetables you like most.
As a runner, it’s all about timing. Kabay suggests saving high-fiber foods for a postrun meal or snack to avoid any discomfort or an unplanned pitstop on the road. Practice eating foods with fiber before a run if you’re going to have them on race day.
Having a more sensitive digestive tract doesn’t mean you have to avoid high-fiber foods entirely, Jones says, even if you’ve been diagnosed with irritable bowel syndrome. Instead, just be mindful of what you eat around run time and see how your body reacts with different foods.
The 10 Best High-Fiber Foods to Add to Your Diet
You’re not going to be able to dramatically increase your fiber intake overnight. However, you can slowly incorporate high-fiber foods, like the ones on this list, to make sure you’re getting sufficient fiber.
*Fiber numbers based on the USDA FoodData Central
1. Artichoke
A medium-size artichoke contains about 7 grams of fiber. There are a ton of different ways you can sneak this vegetable in your diet. You can pair it with spinach for a tasty snack or add it as a pizza topping.
2. Classic Oats
Jones says the best thing about classic oats is you can enjoy them anytime—a sweet bowl for breakfast or savory for dinner. Plus, just a 1/2-cup serving contains 4 grams of fiber. Top it with fruit and you get even more.
3. Pumpkin
Just a cup contains 7 grams of fiber. For breakfast, you can mix this vegetable in with your oatmeal, or whip up a batch of pumpkin muffins.
4. Prunes
If you’re looking for a quick fix for your digestive issues, then you’ve probably solicited prunes or prune juice for help, because just one 1/4 cup contains about 3 grams of fiber. This is a great snack for those who struggle with constipation when traveling. Pack this fruit along with some water to munch on as you travel. Jones says it will help get things moving along a bit smoother.
5. Raspberries
Raspberries are one of the highest fiber fruits that you can find, packing 8 grams per cup. There are a ton of different ways you can add them to your diet, whether you mix into yogurt, a smoothie, oatmeal, or just munch on them for a snack.
6. Blueberries
A cup of blueberries contains about 4 grams of fiber. Make blueberry muffins, add them to smoothies, or just eat them as a snack with other berries. Plus, they’re filled with tons of antioxidants that your body needs for fighting free radicals and staying healthy.
7. Avocado
Add avocado to salads, whip up some guac, or spread it on whole wheat toast. A half of a medium-size avocado has 7 grams of fiber.
8. Medjool Dates
There’s a wide variety of dates, but Medjool dates are a bit softer and sweeter, Kabay says. Just two dates will provide you with 3 grams of fiber. Pack these for some fuel on longer runs or save them as a postrun snack.
9. Almonds
You don’t have to go nuts with this snack, just one ounce of almonds (about 23 in total) has nearly 4 grams of fiber. Mix them into trail mix with dried fruit to get carbs, protein, and healthy fat in one snack.
10. Lentils
Jones says lentils are great for runners because they come in a ton of different varieties—red, green, brown, and yellow. One cup of cooked lentils contains more than 15 grams of fiber, and they’re also rich in iron and protein.
Monique LeBrun joined the editorial staff in October 2021 as the associate health and fitness editor. She has a master’s degree in journalism and has previously worked for ABC news and Scholastic. She is an avid runner who loves spending time outside.
