Nutrient of the Week: Fiber

Fiber is a type of polysaccharide[1] that cannot be digested by human enzymes, thus passing through our digestive system almost untouched. Now, you must be thinking “So what is the point of eating fiber?” First of all, fiber contributes to bowel regularity. Because it goes through the intestines undigested, fiber provides mass and attracts water to the feces. When the stool is large and soft, less pressure is needed, making elimination much easier. A diet poor in fiber can lead to constipation, diverticulitis[2], and hemorrhoids[3]. Also, some population studies have linked an increased fiber intake to a reduced risk of developing colon cancer. Second, foods rich in fiber require more chewing, which will make you eat slower. Several studies[4] have shown that by eating slower, people are more likely to recognize body signs of fullness, and stop eating before they are too full. High-fiber foods also fill you up without yielding many calories. This suggests that fiber may help in weight control. Third, consuming fiber-rich foods can help in regulating blood sugar, because some types of dietary fiber slow glucose absorption, meaning that blood-sugar spikes are less likely to occur. Finally, fiber inhibits the absorption of cholesterol, promoting cardiovascular health.

Now that you know why you should include fiber into your diet, let’s take a look at how to do it. Dietary fiber is a group of substances found in plant foods. Cellulose, hemicelluloses and lignin are structural parts of plants found in whole grains[5]. These fibers are insoluble (don’t dissolve in water) and are not easily metabolized by intestinal bacteria (nonfermentable). Their role is to increase fecal bulk and decrease intestinal transit time. A second group is called soluble or viscous fibers. Pectins, gums, and mucilages represent this group and are found around and inside plant cells. These fibers delay stomach emptying, slow glucose absorption, and can lower blood cholesterol. Major food sources are apples, bananas, oats, barley, beans, and carrots, among others.

Most plant foods contain a combination of insoluble and soluble fibers, but fiber can also be added to foods. This is known as functional fiber and has been shown to provide health benefits. However, experts recommend that you get most of your fiber from foods, rather than supplements. This can be easily accomplished by consuming whole grains, fruits, vegetables, and beans. Keep in mind that the adequate intake for fiber is 25 grams per day for the adult woman.

References

1. Wardlaw, G. and Smith, A. Contemporary Nutrition, seventh edition.
2. Understanding the 2005 Dietary Guidelines for Americans. ACE Continuing Education Course material.