What is dietary fiber?
Dietary fiber, also known as roughage or bulk, includes all parts of plant foods that your body can't digest or absorb.
Unlike other food components such as fats, proteins or carbohydrates — which your body breaks down and absorbs —
fiber isn't digested by your body. Therefore, it passes virtually unchanged through your stomach and small intestine and into
Fiber is often classified into two categories: those that don't dissolve in water (insoluble fiber) and those that do (soluble
- Insoluble fiber. This type of fiber promotes the movement of material through your
digestive system and increases stool bulk, so it can be of benefit to those who struggle with constipation or irregular stools.
Whole-wheat flour, wheat bran, nuts and many vegetables are good sources of insoluble fiber.
- Soluble fiber. This type of fiber dissolves in water to form a gel-like material. It
can help lower blood cholesterol and glucose levels. You can find generous quantities of soluble fiber in oats, peas, beans,
apples, citrus fruits, carrots, barley and psyllium.
The amount of each type of fiber varies in different plant foods. To receive the greatest health benefit, eat a wide variety
of high-fiber foods.
Benefits of a high-fiber diet
A high-fiber diet has many benefits, which include:
- Prevents constipation. Dietary fiber increases the weight and size of your stool and
softens it. A bulky stool is easier to pass, decreasing your chance of constipation. If you have loose, watery stools, fiber
may also help to solidify the stool because it absorbs water and adds bulk to stool.
- Lowers your risk of digestive conditions. A high-fiber diet may lower your risk of
specific disorders, such as hemorrhoids, irritable bowel syndrome and the development of small pouches in your colon (diverticular
- Lowers blood cholesterol levels. Soluble fiber found in beans, oats, flaxseed and oat
bran may help lower total blood cholesterol levels by lowering low-density lipoprotein, or "bad," cholesterol levels.
- Controls blood sugar levels. Fiber, particularly soluble fiber, can slow the absorption
of sugar, which for people with diabetes, can help improve blood sugar levels. A high-fiber diet may also reduce the risk
of developing type 2 diabetes.
- Aids in weight loss. High-fiber foods generally require more chewing time, which gives
your body time to register when you're no longer hungry, so you're less likely to overeat. Also, a high-fiber diet tends to
make a meal feel larger and linger longer, so you stay full for a greater amount of time. And high-fiber diets also tend to
be less "energy dense," which means they have fewer calories for the same volume of food.
- Uncertain effect on colorectal cancer. Evidence that dietary fiber reduces colorectal
cancer is mixed — some studies show benefit, some show nothing and even some show greater risk. If you're concerned
about preventing colorectal cancer, adopt or stick with a colon cancer screening regimen. Regular testing for and removal
of colon polyps can prevent colon cancer.
How much fiber do you need?
How much fiber do you need each day? The National Academy of Sciences' Institute of Medicine, which provides science-based
advice on matters of medicine and health, gives the following daily recommendations for adults:
||Age 50 and younger
||Age 51 and older|
Your best fiber choices
If you aren't getting enough fiber each day, you may need to boost your intake. Good choices include:
- Grains and whole-grain products
- Beans, peas and other legumes
- Nuts and seeds
Refined or processed foods — such as fruit juice, white bread and pasta, and non-whole-grain cereals — are
lower in fiber content. The grain-refining process removes the outer coat (bran) from the grain, which lowers its fiber content.
Similarly, removing the skin from fruits and vegetables decreases their fiber content.
So what foods are your best bets? This list shows the amount of dietary fiber in several types of foods.
||Fiber content in grams*|
|Split peas, cooked, 1 cup
|Red kidney beans, boiled, 1 cup
|Raspberries, raw, 1 cup
|Whole-wheat spaghetti, 1 cup
|Oat bran muffin, medium
|Pear, medium with skin
|Broccoli, boiled, 1 cup
|Apple, medium with skin
|Oatmeal, quick, regular or instant, cooked, 1 cup
|Green beans, cooked, 1 cup
|Brown rice, cooked, 1 cup
|Popcorn, air-popped, 2 cups
|Whole-wheat bread, one slice
*Fiber content can vary between brands.
Source: USDA National Nutrient Database for Standard
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