Why Is Fiber Important for Your Digestive Health?

Fiber is a carbohydrate that the body cannot digest. Yet it is essential for digestive health.

It promotes regularity and prevents constipation. It slows down digestion and keeps blood sugar on an even keel.

Another notable benefit, often overlooked by those outside the medical field, is that fiber acts as fuel for your gut microbiome, that large collection of bacteria, viruses, fungi, and other microbes that live in your gastrointestinal tract. These microbes exist symbiotically with the digestive system and, research shows, support energy harvesting, digestion, and immune defense.

Eamonn Quigley, MD, the chief of gastroenterology and hepatology at Houston Methodist Hospital, says that intact microbiomes protect you from “bad bacteria” that may cause dysbiosis or infection.

“Your immune system is educated by the bacteria in your microbiome," says Dr. Quigley. “And that’s how you learn to live with the microbes and how you learn to benefit from them.”

Read on to find out about good sources of fiber and if you are getting enough to fuel your microbiome.

Are You Getting Enough Fiber?

In order for your gut microbiome to benefit from dietary fiber, you have to ensure you’re getting an adequate amount. A study published in Medicine in Microecology reported that dietary fiber intake is substantially lower today than it was in ancestral populations, especially in high-income countries. This is due in part to industrialization and the rise of a westernized diet that features high levels of processed foods, refined sugars, animal proteins, and saturated fats.

The recommended daily fiber intake for women ages 19 to 50 is 25 grams (g), while men of the same age are encouraged to get 38 g of fiber per day. Women and men over 50 require less fiber in their diets but should still aim for 21 g and 30 g per day respectively. American adults, on average, eat 10–15 g of fiber per day, according to Harvard Health.

Quigley highlights that the long-term repercussions of a low-fiber diet on gut health can be significant, particularly if the pattern is established during childhood. “That’s a time where your microbiome is developing and you may cause changes that can be difficult to reverse,” says Quigley. “If you eat a low-fiber, poor-quality diet, you’re starving your microbes, and ultimately, that’s not going to have good consequences.”

How to Up Your Fiber Intake

The good news is that fiber is relatively easy to incorporate into your daily life, especially when you view it in the context of food, rather than focusing solely on the nutrient itself. A simple shift in perspective might be the catalyst you need to kick-start your journey toward a fiber-rich diet.

Kelly Kennedy, RDN, the manager of nutrition at Everyday Health, works with her patients to identify gradual strategies for including more nutrient-rich foods.

“I wouldn’t say, ‘You need to eat X, Y, and Z,’ because that doesn’t help people to be successful,” Kennedy says. “What would work for me wouldn’t necessarily work for another person. It has to be very personal.”

Kennedy takes a slow but steady approach in part so that patients don’t become overwhelmed, but also because an increase in dietary fiber should be made gradually, according to Cornell University's Gannett Health Services. Too much fiber at once may cause bloating or abdominal pain and may produce rather than prevent constipation, especially if you don’t drink enough water.

Kennedy encourages her patients to make small swaps that build fiber into their diets without eliminating foods they’ve grown up on or have always loved; for example she might suggest substituting whole-wheat pasta for white pasta, or brown rice for white rice. She maintains a “progress over perfection” mindset.

“Continue to try new foods, try different brands, make a swap half of the time or even one-fourth of the time,” she says. “It doesn’t have to be perfect. It’s just about trying to improve and build on where you’re at now.”

Not All Fiber Is Created Equal

There are two main types of dietary fiber, soluble and insoluble, both of which should be part of your diet every day. Plant foods contain both soluble and insoluble fiber, but some are higher in one than the other.

Soluble fiber dissolves in water, per Mayo Clinic, and helps to lower cholesterol, stabilize blood sugar, and slow the absorption of carbohydrates from food. It also softens stool. Good sources of soluble fiber include:

• Oats
• Apples
• Nuts
• Seeds
• Legumes
• Berries
• Citrus fruits

Insoluble fiber attracts water to the intestine, which adds bulk to stool and promotes the movement of waste products through your digestive system. It can be extremely beneficial for people who struggle with constipation and irregularity. Good sources of insoluble fiber include:

• Whole grains
• Green beans
• Nuts
• Vegetables such as cauliflower, carrots, green beans, and potatoes

“Variety is just as important as getting enough fiber,” Kennedy says.

Easy Ways to Add Fiber

Here are some tips from Harvard T.H. Chan School of Public Health for incorporating more fiber into your diet.

• Opt for whole fruits rather than fruit juices.
• Swap white rice, bread, and pasta for whole grains that are minimally processed, such as brown rice, whole-wheat bread, farro, and quinoa. Look for bread that lists “whole wheat” “whole-wheat flour” or another whole grain as the first ingredient.
• Include high-fiber foods in current meals — add 1 to 2 tablespoons of almonds or chia seeds to cereal, add diced vegetables to casseroles, or substitute beans or legumes for meats in soups.
• Make snacks count by eating fresh fruits, raw vegetables, low-fat popcorn, whole grain crackers, or nuts.
• Drink plenty of water to prevent constipation.
• Avoid refined, added, and processed sugars as much as possible. These do not benefit your gut microbiome.

What About Fiber Supplements?

Fiber supplements are another simple way to increase your fiber intake, though they are not intended to completely replace high-fiber foods. Supplements don’t offer the same variety of nutrients that whole foods do. Supplements are just that — supplementary — and should be used to amplify, not substitute for a high-fiber diet.

Acknowledging the connection between fiber and a flourishing gut microbiome is the first step on a journey toward optimal gut health. A thriving gut, in turn, lays the groundwork for overall health and well-being. “I think we’re only just beginning to scratch the surface,” says Kennedy. “I think [the gut microbiome] is the future of nutrition and one of the most important things for people to focus on for good health.”

Additional reporting by Megan Mikaelian.