All About Dietary Fiber

High Fiber Foods

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Fiber isn’t just a powdered supplement sold at your local health food store! Fiber, which consists of the indigestible components of plant foods we consume, is found in the cell walls and indigestible residues of plants such as fruits, vegetables, legumes, nuts, seeds, and grains.  There are various different types of fiber, but the principle classifications are soluble or insoluble.  The main difference is that soluble fiber dissolves in water and insoluble doesn’t. Both types of fiber are essential components of a healthy diet.

Health Benefits of Fiber

Irishman Denis Burkitt is credited with establishing many of the original links between a lack dietary fiber and an increase in chronic disease. In fact, he became known as “Fiber Man” in the ’70s! Burkitt found many diseases and conditions that were common in Western society–including cardiovasular diseases, diabetes, and constipation–were next to nonexistent in Africa, where dietary intake of fiber was significantly higher. So even though fiber is is indigestible, it’s crucial for good health. Both soluble and insoluble fiber are are associated with reduced risk for various conditions, including (but not limited to) the following:

Heart Disease
Fiber consumption has been shown to decrease cholesterol and blood pressure, and several studies have shown that people with the highest levels of fiber consumption appear to have the lowest lifetime risk of cardiovascular disease.

A diet high in fiber appears to help diabetics improve their ability to control blood sugar. It can also help as a preventive measure to help reduce the risk of developing diabetes. The exact mechanism is unclear, but may involve increased insulin sensitivity and slowing glucose absorption from the gut.

When soluble fiber binds with water in the stomach, it forms a gelantinous mass that promotes satiety. In other words, eating foods high in fiber makes you feel fuller faster, and may help you feel fuller for longer, helping to stave off hunger and prevent overeating. Fiber may also help with weight control by minimizing cravings.

Colon and Rectal Health
Some early studies suggested a connection between high-fiber diets and and reduced risk of colon cancer, but more recent, in-depth studies have failed to confirm that a diet high in fiber lowers the risk of developing colon adenomas, which are the precursors of cancer. Nevertheless, fiber does appear to have a positive effect on colorectal health in other ways. For example, while colon and rectal cancers are not caused by a lack of fiber, in susceptible individuals, fiber may help prevent the disease.

In addition, fiber helps prevent and relieve constipation and hemorrhoids. Insoluble fiber helps move waste through the digestive tract and provides bulk to the feces. Soluble fiber helps soften stools. Together, they promote regular bowel movements that are easy to pass, thereby treating constipation and helping you avoid the strain that can trigger or worsen an existing case of hemorrhoids.

Healthy Dietary Sources of Fiber

How much fiber should you consume daily? The Institute of Medicine (IOM), which provides science-based advice on matters of medicine and health, recommends that women consume 25 grams of fiber per day, and that men get 38 grams per day.

Examples of soluble fiber include: apples, barley, beans, Brussels sprouts, cucumbers, flaxseeds, lentils, oatbran, oatmeal, pears, and psyllium.

Examples of insoluble fiber include:  brown rice, bulgur, cabbage, carrots, cucumbers, celery, dark leafy greens, green beans, wheat bran, whole grains, and the skins of fruit and root vegetables.

How to Increase Your Dietary Fiber

As you begin including more fiber in your diet, it’s important to start slowly to allow your body to acclimate. Introduce high-fiber foods gradually over a period of two to four weeks to avoid or lessen side effects such as bloating, gas, diarrhea, and constipation. Here are a few more practical tips for getting more fiber in your diet.

  • Stay hydrated. Drink at least 8 glasses of water a day.
  • Choose whole foods only (eliminate processed foods).
  • If you buy a packaged food, ensure it includes at least 4 to 5 grams of fiber per serving.
  • Replace all white and processed foods with whole grains.
  • Start your day with a whole grain.
  • Increase your daily intake of fruits (especially berries) and vegetables.
  • Aim to consume at least 1 to 2 servings of leafy greens every day.


Pereira MA, O’Reilly E, Augustsson K, et al. Dietary fiber and risk of coronary heart disease: a pooled analysis of cohort studies. Arch Intern Med. 2004; 164:370-6.

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The One Medical blog is published by One Medical, an innovative primary care practice with offices in Boston, Chicago, Los Angeles, New York, Phoenix, the San Francisco Bay Area, Seattle, and Washington, DC.