Why It’s Healthy (Not Just for Your Gut)

Dietary fiber, sometimes called “roughage,” is primarily known for adding “bulk” to bowel movements. Most North American adults don’t get enough of it, consuming about 17 grams of fiber daily (compared to the recommended 25 to 30 grams). Dietary fiber helps digestion and protects against health conditions such as cardiovascular disease, diabetes, and some cancers.

Dietary fiber is a carbohydrate that is not easily digestible. It can be soluble (able to dissolve in water) or insoluble (unable to dissolve in water).

This article will discuss some types of dietary fiber, how they affect the body, the potential health benefits of a high-fiber diet, considerations to take before upping your fiber intake, and what foods to eat to get more fiber into your diet.

Why Dietary Fiber Is Good for You

Maintaining a high-fiber diet has specific health benefits and can improve your overall health. Two meta-analysis studies found a reduced risk of 15–16% of all-cause mortality (deaths due to any cause) in those who consume high levels of fiber compared to those who consume lower levels of fiber.

A 2022 study found a 25% reduction in all-cause mortality for those consuming the most fiber compared with those consuming the least fiber.

Research suggests dietary fiber can benefit digestion, inflammation, heart disease, type 2 diabetes, breast cancer, and colorectal cancer.

More detail on these benefits is outlined below.

Digestion

Dietary fiber is most associated with digestion, particularly in preventing and relieving constipation. Fiber affects digestion in different ways, depending on the type of fiber.

Soluble fiber:

• Creates a gel that binds to water
• Helps to soften and bulk stool

Insoluble fiber:

• Mildly irritates the intestinal lining, stimulating the secretion of water and mucus
• Encourages movement of stool

Some forms of fiber can act as probiotics (food for gut bacteria), which help to increase water in the intestines and make stools softer and easier to pass.

Consuming a variety of high-fiber foods to ensure you get a range of fiber types, drinking adequate amounts of water, and getting regular exercise can work together to prevent or relieve constipation.

Large cohort studies have found dietary fiber may help protect against diverticular disease (small pouches in the lower intestine). Fiber found in whole fruits and vegetables (including their skins), and cereal grains have proved particularly beneficial.

Inflammation

Some studies have found an association between higher dietary fiber intake and lower systemic inflammation. A 2022 study of older adults associated cereal fibers with lower levels of various inflammation markers than those from fruits and vegetables.

Low-grade systemic inflammation may increase the risk of certain conditions, such as cardiovascular disease (CVD) and cancer. More research is necessary to determine the role dietary fiber may play in reducing inflammation and preventing related conditions.

Heart Disease

Epidemiological studies (the study of how often and why diseases occur in certain groups of people) have found an association between a high dietary fiber intake—particularly cereal fibers—and a lower risk of heart disease and deaths from CVD.

“Cereal fiber” does not mean boxed breakfast cereals specifically, but rather the seeds of whole grains that contain germ, bran, and endosperm and are minimally refined. Cereal grains may include:

• Quinoa
• Steel cut oats
• Millet
• Brown rice
• Buckwheat
• Barley

Some researchers believe soluble fiber may bind to bile acids in the digestive tract and help remove them from the body. The liver would then pull cholesterol from the blood to make new bile acids, lowering cholesterol. A meta-analysis that examined 67 controlled trials found that soluble dietary fiber had a modest positive effect in reducing total and low-density lipoprotein (LDL, or “bad”) cholesterol.

A 2022 study found that a high-fiber diet could help improve blood pressure in people with hypertension (high blood pressure), whether or not they were on antihypertensives (medications for lowering high blood pressure).

Research suggests a high fiber intake may also help lower the risk of metabolic syndrome (a combination of high blood pressure, high insulin levels, excess weight, high triglyceride levels, and low high-density lipoprotein cholesterol, otherwise known as HDL, or the “good cholesterol). Metabolic syndrome can increase the risk of developing heart disease and type 2 diabetes.

Type 2 Diabetes

Fiber can help maintain lower blood sugar levels. The body can’t break down or absorb fiber, so it doesn’t cause the blood sugar spike associated with other carbohydrates.

Fiber helps to delay the absorption of sugars from the intestines into the blood, reducing the likelihood of a surge of insulin.

Fiber can also help protect against weight gain, which can contribute to developing type 2 diabetes. The gel formed by soluble fiber slows down digestion, which can help make you feel fuller for longer. High-fiber foods also tend to be less energy-dense, meaning high-fiber food can have fewer calories than the same amount of lower-fiber food.

Breast Cancer

A study involving more than 90,000 women who had not yet been through menopause found a 25% reduced risk of breast cancer when comparing the highest to the lowest fiber intake. A meta-analysis of 17 prospective cohort studies found similar results, with fiber noted as protective from breast cancers both before and after menopause.

There is also an association between a high-fiber diet and a lower risk of benign breast disease, a risk factor in adolescents for later developing breast cancer.

Colorectal Cancer

Studies have found that fiber may offer some protection against certain subtypes of colorectal cancer (CRC). Fibers from fruits, vegetables, and legumes showed some protection against CRC, but cereal fibers were more highly associated with a lower risk of CRC.

Fiber may help reduce the risk of bowel cancer by:

• Increasing the bulk of stool
• Diluting possible carcinogens from the diet
• Decreasing the time it takes stool (and possible carcinogens) to travel through the colon
• The production of short-chain fatty acids made by the bacterial fermentation of some forms of fiber

Food Sources High in Dietary Fiber 

Strive to take in 100% of the daily value (DV) of dietary fiber each day. Foods are considered high in fiber if they contain 20% or more DV of dietary fiber per serving. Foods with 5% or less DV of dietary fiber per serving are considered low fiber.

Foods that contain dietary fiber include:

• Fruits and vegetables
• Whole grains and foods made with whole-grain ingredients
• Beans, peas, and lentils
• Nuts and seeds
• Wheat bran

For soluble fiber, try foods such as:

• Apples
• Blueberries
• Oatmeal
• Nuts
• Beans
• Lentils

For insoluble fiber, try foods such as:

• Whole wheat products, particularly wheat bran
• Brown rice
• Quinoa
• Legumes
• Almonds
• Walnuts
• Seeds
• Leafy green vegetables, like kale
• Fruits with edible skins, like apples and pears

Most people should be able to get enough fiber through their diets and not require fiber supplements. Foods can provide a variety of fiber types as well as other nutrients and phytochemicals that may work with fiber, while supplements tend to be more isolated. Talk to your healthcare provider if you can’t meet your fiber needs through your diet alone.

How Much Dietary Fiber Do You Need Daily?

The general recommendation for American adults is 25–30 grams of fiber daily from food sources, not supplements.

This is based on a 2,000-calorie-per-day diet and may not suit everyone. To calculate your recommended daily dietary fiber intake, you can use the formula of 14 grams of dietary fiber per 1,000 calories of food.

For children, you can estimate how much fiber your child needs per day by adding five or 10 to their age. For example:

• Age 5: 10–15 grams per day
• Age 10: 15–20 grams per day
• Age 15: 20–25 grams per day

These amounts are general guidelines. Talk to your healthcare provider to determine what is best for you or your child.

Who Should Be Mindful of Dietary Fiber Intake

Very high-fiber diets of more than 40 grams per day may decrease the absorption of some minerals, such as zinc, iron, and calcium, which could lead to deficiencies in susceptible people.

Some people with inflammatory bowel disease (IBD) may be sensitive to some dietary fibers. People with IBD often have certain missing or malfunctioning microbes, which can make β-fructan fibers hard to ferment. You can find these fibers in garlic, artichokes, asparagus, chicory roots, and bananas. Certain unfermented fibers have been found to increase inflammation and make symptoms worse in some people with IBD.

Symptoms of Too Much Dietary Fiber 

If you want to increase your fiber intake, start slowly, eating more fiber every few days and drinking plenty of water. Too much fiber at once can cause digestive problems such as:

Summary

Dietary fiber is a carbohydrate that humans cannot easily digest. It may be soluble or insoluble.

Dietary fiber offers many health benefits, including helping with digestion and relieving constipation. It may also protect against inflammation, heart disease, type 2 diabetes, breast cancer, and colorectal cancer.

Foods that contain dietary fiber include fruits and vegetables, whole grains, wheat bran, beans, peas, lentils, nuts, and seeds.

The general recommended dietary fiber intake is 25–30 grams per day. If you are increasing your fiber intake, do so slowly to avoid digestive discomfort.

Talk to your healthcare provider before taking fiber supplements.