Nutrition Science and Everyday Application - beta v 0.1

214 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
1. Soluble Fiber – These fibers dissolve in water, forming a viscous gel in the GI tract,
which helps to slow digestion and the absorption of glucose. This means that
including soluble fiber in a meal helps to prevent sharp blood sugar spikes, instead
making for a more gradual rise in blood glucose. Consuming a diet high in soluble
fiber can also help to lower blood cholesterol levels, because soluble fiber binds
cholesterol and bile acids (which contain cholesterol) in the GI tract. Soluble fiber is
also highly fermentable, so it is easily digested by bacteria in the large intestine.
Pectins and gums are common types of soluble fibers, and good food sources
include oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and
vegetables. (Psyllium fiber supplements like Metamucil are composed mainly of
soluble fiber, so if you’ve ever stirred a spoonful of this into a glass of water, you’ve
seen the viscous consistency characteristic of soluble fiber.)
2. Insoluble Fiber – These fibers typically do not dissolve in water and are
nonviscous. Some are fermentable by bacteria in the large intestine but to a lesser
degree than soluble fibers. Insoluble fibers help prevent constipation, as they
create a softer, bulkier stool that is easier to eliminate. Lignin, cellulose, and
hemicellulose are common types of insoluble fibers, and food sources include
wheat bran, vegetables, fruits, and whole grains.
FOOD SOURCES OF DIETARY FIBER
Since fiber provides structure to plants, fiber can be found in all whole plant foods,
including whole grains (like oatmeal, barley, rice and wheat), beans, nuts, seeds, and whole
fruits and vegetables.
Figure 4.23. A bowl of oatmeal topped with blueberries and sunflower seeds.
This meal is packed with fiber from the oatmeal, blueberries, and sunflower seeds.
When foods are refined, parts of the plant are removed, and during this process,
fiber and other nutrients are lost. For example, fiber is lost when going from a whole fresh
orange to orange juice. A whole orange contains about 3 grams of fiber, whereas a glass of
orange juice has little to no fiber. Fiber is also lost when grains are refined. We will discuss
this more a little later.