Agriculture Reference
In-Depth Information
Figure
2.12.
Fat, carbohydrate fiber, vitamin, and mineral content of selected meats and nuts.
Note that vitamins are in micrograms (mcg) but still using the left-hand numbering. (Data from
Agricultural Research Service Nutrient Data Laboratory USDA National Nutrient Database for
Standard
Reference,
Release
17,
http:
//
www.nal.usda.gov
/
fnic
/
foodcomp
/
Data
/
SR17
/
reports
/
sr17page.htm.)
Another aspect of protein is that the body has no means to store either protein or
amino acids. On the other hand the body can store fat and can convert carbohydrates
to fat, which is thus a way to store carbohydrates. This creates a problem in that if
the diet does not contain sufficient protein the body can only get needed amino acids
from already formed muscle and thus muscle wasting will occur.
2.5
CARBOHYDRATES
Figure 2.13 shows a two-sugar unit of a larger polysaccharide. Carbohydrates are
mostly made up of polysaccharides and are common in nature and food except meat
as noted above. They are the chief source of energy in most diets also as noted
above. Carbohydrates can be simple, as in the case of single-sugar molecules or as
two-sugar molecules bonded together. They can also be complex such as the starches
found in seeds, grain, and root crops. Simple sugars are readily taken up and used by
the body, while complex carbohydrates must be broken down before absorption.
The glucose molecule shown in Figure 2.13 is readily taken up by the body and
used to produce energy. The disaccharide, sucrose, common table sugar, must first
be broken into its two constituent sugar molecules before use. Sucrose is made up of
two sugars that are only different in the arrangement of their 22OH and 22C55O sub-
stituents. However, both types of sugars are readily metabolized in the body and thus
provide a rapid source of energy.
Sugar molecules can be bonded together in different ways producing many diffe-
rent polymers that are significantly different from starch. Thus, although both cellulose
