Fiber: Is It Good or Bad for Constipation?

Fiber is a substance found in plant foods such as fruits, vegetables, nuts, and beans. It’s indigestible, which means your body can’t digest or absorb it.

There are two main types of dietary fiber:

• Soluble fiber: Soluble fiber can be fermented — broken down — by bacteria that live in your large intestine. Foods such as oats, beans, fruits, and root vegetables contain soluble fiber.
• Insoluble fiber: Unlike soluble fiber, insoluble fiber can’t be fermented by gut bacteria and passes through your digestive system unchanged. It’s concentrated in the skin of fruits, nuts, veggies, and whole grains.

Keep in mind that there are different types of soluble fiber separated by solubility, viscosity, and fermentability. In this article, we’re keeping it simple. If you want to learn more about the different categories of fiber, check out this comprehensive guide.

Most high fiber foods contain a combination of the two types, but some are higher in insoluble fiber while others are higher in soluble fiber.

Insoluble fiber adds bulk to your poop and helps food move comfortably through your gastrointestinal system. Soluble fiber draws water into your poop, which helps keep it soft and easy to pass.

Another benefit of soluble fiber is that your gut bacteria break it down into beneficial compounds called short-chain fatty acids.

Short-chain fatty acids such as butyrate, propionate, and acetate help fuel the cells that line your gut, reduce intestinal inflammation, and stimulate the production of mucus, which protects your gut lining and helps keep it lubricated in order to pass poop comfortably.

As you can see, fiber is pretty important for your digestive system. It should be no surprise that a diet low in fiber can lead to a number of issues, including constipation.

How much fiber should you be eating?

Current recommendations for fiber intake are:

• 38 grams per day for men ages 19 to 50
• 25 grams per day for women ages 19 to 50
• 30 grams per day for men over 50
• 21 grams per day for women over 50

Hitting these fiber intake goals not only supports digestive health and reduces the risk of constipation but can also help protect against heart disease, colon cancer, and a number of other health issues.

Unfortunately, modern diets are often too low in fiber because many people rely on ultra-processed, low fiber foods for fuel. The average American consumes about 15 grams of fiber per day, which is well below the amount recommended to promote optimal health. This lack of fiber is one of the reasons constipation is so prevalent in the United States.

Research has shown that a low fiber diet increases the risk of constipation. Researchers consider low fiber intake a main cause of constipation.

Many other factors, such as dehydration and underlying medical conditions, can contribute to constipation. But some research suggests that increasing dietary fiber intake may be an effective way to improve constipation.

A 2022 review of 11 studies found that increasing intake of fruits such as kiwis and prunes could help improve constipation by softening stool, improving stool frequency, and improving gut bacteria balance.

Another 2022 study found that adults with mild constipation who followed a high fiber diet for 4 weeks experienced significant improvements in constipation severity and overall quality of life.

Increasing fiber intake through fiber supplements also seems to be helpful for improving constipation symptoms.

Although findings from a number of studies suggest that increasing fiber intake can be a helpful and relatively easy way to support digestive health and improve mild constipation, more research is needed on its effect on severe constipation.

Constipation can have a number of causes. If your constipation isn’t getting better with dietary changes, it may be time to talk with a doctor. They can look for other potential causes and recommend treatment options that can help you feel better.

While many fibers can help soften your poop and help you have more comfortable bowel movements, certain fibers can actually make constipation worse.

Research suggests that fibers such as soluble wheat dextrin and ground insoluble wheat bran can decrease the water content of your poop. They pull water from your stool, which can make it hard to pass.

Also, people with medical conditions that cause constipation, such as irritable bowel syndrome with constipation (IBS-C), may find that certain foods trigger or worsen constipation.

For example, foods high in fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs) may make constipation symptoms worse. Many high FODMAP foods are rich in fiber.

Some studies have shown that a low FODMAP diet leads to improvements in all IBS subtypes, including IBS-C. However, low FODMAP diets seem to be most effective for people with diarrhea-predominant IBS (IBS-D).

If you have constipation, you can try to increase your fiber intake to see whether it helps your symptoms.

It’s best to add fiber to your diet gradually. Increasing your intake suddenly or eating too much fiber at once can cause gas and bloating.

If you increase your fiber intake, it’s important to bump up your water intake too. Increasing both water consumption and fiber intake has been shown to be more effective for treating constipation than increasing fiber intake alone.

Here are some foods high in soluble fiber, including foods that have been specifically shown to improve constipation:

• fruits such as kiwis, prunes, citrus fruits, berries, avocados, and apples
• legumes such as black beans, chickpeas, and lentils
• vegetables such as sweet potatoes, carrots, and broccoli
• nuts and seeds
• oats, quinoa, and buckwheat
• flaxseed and chia seeds

Certain foods, such as kiwis, seem to be particularly helpful for constipation. A 2021 study that included 79 people with chronic constipation found that those who ate two kiwis per day for 4 weeks experienced significant improvements in poop consistency, straining, and bowel movement frequency.

Plus, the people who ate kiwis were less likely to report treatment-related side effects than people who took psyllium husk or ate prunes.

Some fiber supplements can be helpful for treating constipation.

Psyllium fiber is a type of soluble fiber that forms a gel when it comes into contact with water. It helps soften poop consistency by drawing water into stools, which can improve constipation symptoms.

It’s currently the only type of fiber recommended by the American College of Gastroenterology to treat chronic constipation and IBS.

A 2022 review found that, when taken in doses of more than 10 grams per day for at least 4 weeks, psyllium is effective for improving constipation symptoms. Other fiber supplements, such as pectin, may be helpful as well.

Fiber supplements can cause side effects, including bloating and gas, and some types can make constipation worse. To be on the safe side, it’s best to ask a doctor for advice before taking a fiber supplement for constipation.

A doctor can tell you whether a fiber supplement is appropriate for your specific health needs. They can also help you pick out the right kind of fiber and give you safe and effective dosing suggestions.

Fiber is important for digestive health and can help keep your poop soft and easy to pass.

Some research suggests that low fiber diets may be a risk factor for constipation and that increasing fiber intake can help reduce constipation symptoms such as infrequent bowel movements and straining.

If you’re dealing with constipation, you can work with a doctor or a registered dietitian, if you have access to one, to develop a higher fiber diet that includes foods such as fruits, vegetables, and beans.

But remember, not all cases of constipation are caused by a lack of fiber. If increasing your fiber intake doesn’t improve your constipation symptoms, reach out to a doctor for treatment advice.