Agriculture Reference
In-Depth Information
must be eaten as part of the diet. Octadecadienoic acid is commonly found in milk fats,
while in general animal fats are sources of both these essential fatty acids.
2.7
FIBER
Fiber represents all those components of food that are not digested by the body and pass
through unchanged. There are two types of fiber, soluble, specifically water soluble and
insoluble, and each play a different role in the diet. Insoluble fiber helps move food
through the body and makes elimination easier. Soluble fiber also helps move food
through the digestive system, but in addition it absorbs fat and can thus decrease fat
uptake and the potential adverse effects of fat on health. Although all foods, except
meats, have some of both types of fiber, grains, fruits, and vegetables vary widely in
the amount of each that they have.
Fruits, barley, and oats have soluble fiber, while wheat and brown rice are noted for
having insoluble fiber. Legumes, seeds, and vegetables in general are noted for having
insoluble fiber. Soluble fiber includes things such as gums, mucliages, and pectins,
while insoluble fiber is composed of cellulose, lignin, and some hemicelluloses.
Examples of the molecular structure of two fibers is given in Figure 2.18. A balanced
diet containing a mixture of fruits, vegetables, and whole grains will contain a suitable
mixture of both kinds of fiber.
Generally, the more processing a food is subject to the less fiber it contains. For
instance, components such as skin and core are removed from fruits and the remaining
portion strained. Each step will remove some fiber and thus make the food less desirable
as a fiber source. Grain as it comes from the field has outer layers that are darker, com-
monly brown, in color. These outer layers are often removed during processing making
Figure
2.18.
Two types of dietary fiber, pectan and cellulose.
