Fiber is also known as roughage. It is the indigestible part of plant foods that pushes through our digestive system, absorbing water along the way and easing bowel movements.
The word fiber comes from the Latin word fibra, meaning thread, string, filament, entrails. Dietary fiber refers to nutrients in the diet that are not digested by gastrointestinal enzymes.
In this article, we will look at the different types of fiber, why they are important and what foods are high in fiber.
Contents of this article:
Fast facts on fiber
Here are some key points about fiber. More detail and supporting information is in the main article.
- Fiber can also referred to as roughage or bulk
- Fiber is often split into two types: soluble and insoluble
- Dairy products and white bread are low in fiber
- Cereal grains, seeds and fruits are high in fiber
- Gut motility is aided by fiber in the diet
- Fiber helps speed up the elimination of toxic waste through the colon
- Insoluble fiber helps maintain the correct pH range
- Soluble fiber can reduce cholesterol levles
- Kidney beans, pinto beans and brussels sprouts all contain soluble fiber
- The recommended daily amount of fiber is 25 g for women and 38 g for men.
Soluble and insoluble fiber
Fiber is made up of non-starch polysaccharides, such as cellulose, dextrins, inulin, lignin, chitins, pectins, beta-glucans, waxes and oligosaccharides. The word fiber is misleading, because many types of dietary fibers are not fibers at all.
There are two broad types of fiber, soluble and insoluble.
- Soluble fiber dissolves in water. It changes as it goes through the digestive tract, where it is fermented by bacteria. As it absorbs water it becomes gelatinous
- Insoluble fiber does not dissolve in water. As it goes through the digestive tract it does not change its form.
Dietary fiber foods are generally divided into predominantly soluble or insoluble; both types of fiber are present in all plant foods, but rarely in equal proportions.
According to Dr. Warren Enker1, Vice Chairman, Department of Surgery, Beth Israel Medical Center, a good diet involves watching your calorie count, including food rich in nutrients and vitamins, avoiding saturated fats, and paying particular attention to all sources of fiber.
Below is a selection of foods that contain high amounts of fiber.
|Cereal grains - ½ cup cooked||Soluble||Insoluble|
|Psyllium seeds ground (1 Tbsp)||5g||6g|
|Fruit (1 medium fruit)||Soluble||Insoluble|
|Blackberries (½ cup)||1g||4g|
|Citrus Fruit (orange, grapefruit)||2g||2-3g|
|Prunes (¼ cup)||1.5g||3g|
|Legumes (½ cup cooked)||Soluble||Insoluble|
|Lentils (yellow, green, orange)||1g||8g|
|Black eyed Peas||1g||5.5g|
|Vegetables (½ cup cooked)||Soluble||Insoluble|
On the next page, we look at the functions and benefits of soluble and insoluble fiber.