Dietary fiber, also known as roughage, is the indigestible part of plant foods. Fiber has a host of health benefits, including reducing the risk of heart disease and type 2 diabetes.

Fiber is mostly in vegetables, fruits, whole grains, and legumes. There are two types of fiber — soluble and insoluble — and both play important roles in health:

  • Insoluble fiber does not dissolve in water and adds bulk to the stool, preventing constipation.
  • Soluble fiber absorbs water, forming a gel-like substance in the digestive system. Soluble fiber may help lower cholesterol levels and help regulate blood sugar levels.

This article looks at the different types of fiber, why they are important, and suggests some healthful fiber-rich foods.

a bowel of oatmeal which is a good source of dietary fiberShare on Pinterest
Oats, fruit, and nuts are all good sources of soluble fiber.

Dietary fiber is an essential part of a healthful diet. It is crucial for keeping the gut healthy and reducing the risk of chronic health conditions.

Most people in the United States do not get enough fiber from their diets. According to some estimates, only 5% of the population meet the adequate intake recommendations. This means that most people in the U.S. could get health benefits from increasing their daily fiber intake.

Eating fiber has many health benefits:

Protection against heart disease

Several studies over the past several decades have examined dietary fiber’s effect on heart health, including preventing cardiovascular disease and reducing blood pressure.

A 2017 review of studies found that people eating high fiber diets had significantly reduced risk of cardiovascular disease and lower mortality from these conditions.

The authors say that these heart protective effects could be because fiber reduces total cholesterol and low-density lipoprotein (LDL) cholesterol, also called ‘bad cholesterol,’ which is a major risk for heart conditions.

Better gut health

Fiber is important for keeping the gut healthy. Eating enough fiber can prevent or relieve constipation, helping waste to move smoothly through the body. It also encourages healthy gut microbiota.

According to a 2015 review, dietary fiber increases the bulk of stool, helps promote regular bowel movements, and reduces the time that waste spends inside the intestines.

According to a 2009 review, dietary fiber has a positive impact on gastrointestinal disorders, including:

  • colorectal ulcer
  • hiatal hernias
  • gastroesophageal reflux disease
  • diverticular disease
  • hemorrhoids

A 2019 review reports that fiber intake may reduce a person’s risk of colorectal cancer.

Reduced diabetes risk

Adding more fiber to the diet may also have benefits for diabetes. Fiber can help slow down the body’s absorption of sugar, helping to prevent blood sugar spikes after meals.

A 2018 review reports that people who ate high fiber diets, especially cereal fiber, had a lower risk of developing type 2 diabetes. These individuals also reported a small reduction in blood glucose levels.

Weight management

For people aiming to lose weight, a diet high in dietary fiber can help regulate weight loss. High fiber foods help a person feel fuller for longer and may help people adhere to a diet.

In a 2019 study, researchers concluded that people who increased their dietary fiber intake increased their weight loss and adherence to their dietary caloric restriction.

Fiber includes nonstarch polysaccharides, such as cellulose, dextrins, inulin, lignin, chitins, pectins, beta-glucans, waxes, and oligosaccharides.

Soluble and insoluble are the two types of dietary fiber.

Most high fiber containing foods have both insoluble and soluble fiber, so people do not need to think much about the difference. Instead, they can focus on overall fiber intake.

Soluble fiber

Soluble fiber dissolves in water and forms a gel-like substance in the stomach. Bacteria later break the gel down in the large intestine. Soluble fiber provides some calories to the individual.

Soluble fiber provides the following benefits:

  • lowering LDL cholesterol in the blood by affecting how the body absorbs dietary fat and cholesterol
  • slowing absorption of other carbohydrates through digestion, which can help regulate blood sugar levels

Good sources of soluble fiber include:

  • beans
  • fruits
  • oats
  • nuts
  • vegetables

Insoluble fiber

Insoluble fiber does not dissolve in water and passes through the gastrointestinal tract, mostly intact. It does not provide calories.

Insoluble fiber helps build bulk in the stool, helping a person pass stool more quickly. It can also help prevent constipation.

Good sources of insoluble fiber include:

  • fruits
  • nuts
  • vegetables
  • whole grain foods

According to the Academy of Nutrition and Dietetics, the recommended intake for dietary fiber in a 2,000 calorie diet is:

  • 25 grams (g) per day for adult females
  • 38 g per day for adult males

People need less fiber after 50 years of age at around 21 g for women and 30 g for men. During pregnancy or breastfeeding, women should aim for at least 28 g per day.

Learn more about daily fiber recommendations.

Plant-based foods are an excellent source of dietary fiber. Some types have more fiber than others. Read about 38 high fiber foods here.

The following are some examples with their fiber contents, according to the Dietary Guidelines for Americans 2015–2020:

Food Serving size Calories Dietary fiber in g
High fiber bran (ready-to-eat cereal) ½–3/4 of a cup 60–81 9.1–14.3
Chickpeas, canned 1/2 a cup 176 8.1
Lentils, cooked 1/2 a cup 115 7.8
Pinto beans, cooked 1/2 a cup 122 7.7
Black beans, cooked ½ a cup 114 7.5
Lima beans, cooked 1/2 a cup 108 6.6
White beans, canned ½ a cup 149 6.3
Kidney beans 1/2 a cup 112 5.7
Wheat bran flakes (ready-to-eat cereal) 3/4 of a cup 90–98 4.9–5.5
Raw pear 1 medium fruit 101 5.5
Baked beans, canned, plain 1/2 a cup 119 5.2
Avocado 1/2 a cup 120 5.0
Mixed vegetables, cooked from frozen 1/2 a cup 59 4.0
Raspberries ½ a cup 32 4.0
Blackberries 1/2 a cup 31 3.8
Collards, cooked 1/2 a cup 32 3.8
Sweet potato, baked in skin 1 medium vegetable 103 3.8
Popcorn, air-popped 3 cups 93 3.5
Almonds 1 ounce (oz) 164 3.5
Whole wheat spaghetti, cooked 1/2 a cup 87 3.2
Orange 1 medium fruit 69 3.1
Banana 1 medium fruit 105 3.1
Oat bran muffin 1 small muffin 178 3.0
Pistachios, dry roasted 1 oz 161 2.8
Pecans, oil roasted 1 oz 203 2.7
Quinoa, cooked half a cup 111 2.6

People who are allergic to high fiber foods can find it difficult to get enough fiber. They should speak to their doctor about finding sources of fiber that will not cause an allergic reaction.

In some cases, a person may want to talk to their doctor about fiber supplements. A doctor may recommend these if the individual has constipation or trouble passing stool. Pharmacies sell fiber supplements, such as Metamucil, Citrucel, and FiberCon.

These products do not provide the same levels of vitamins and nutrients as natural, high fiber foods, but they are beneficial when someone cannot get enough fiber from their diet.

Eating too much fiber can cause bloating, gas, and constipation. These side effects may occur if a person consumes more than 70 g of fiber a day. This is uncommon but may happen if someone is following a vegan, raw, or whole food diet.

Learn more about the symptoms and effects of eating too much fiber.

People can boost their daily fiber intake by making a variety of small changes:

  • eat fruits and vegetables with the skins on, as the skins contain lots of fiber
  • add beans or lentils to salads, soups, and side dishes
  • replace white breads and pastas for whole wheat versions
  • aim to eat 4.5 cups of vegetables and 4.5 cups of fruit each day, as the American Heart Association suggest
  • if unable to meet the daily requirements, consider using fiber supplements

Dietary fiber is an essential component of a healthful diet, with research linking a high fiber diet with reduced risks of many health conditions, including cardiovascular disease, type 2 diabetes, and certain cancers. Fiber is also important for keeping the gut healthy.

Most people in America do not meet their adequate daily requirement of fiber. People can increase this measure by eating more high fiber foods, fruits and vegetables with the skins on, or by taking fiber supplements if this is not possible.