Agriculture Reference
In-Depth Information
2.10
HOW THE BODY USES NUTRIENTS
All parts of the body must have a continuous supply of energy to function. Carbo-
hydrates, both simple and complex, are the body's primary source of energy.
Complex carbohydrates are broken down by several different enzymes into simple
sugars. At this point they are either immediately used for energy or stored in the
body as lipids. When carbohydrates or sugars are not available, the body can use
either fats or even protein to produce energy.
The body's use of lipids is much more complex than that of carbohydrates in that
they are involved in both energy storage and in essential structures' cellular
components. All cell membranes contain lipids, and thus this component provides an
essential structural component of the body. Cell membranes control the flow of all com-
ponents in and out of the cell, and the lipid portion is important in this control.
However, a high-lipid diet is not recommended for adults as it results in obesity and
contributes to health problems such as heart disease and diabetes. However, a
low-fat diet is not recommended for children because they need both the additional
calories and essential fats for growth.
The major use of proteins is the production of muscle, which includes the heart as
well as those muscles needed for breathing and movement. They are also used to con-
struct other essential components such as connective tissue and enzymes. Amino acids
from protein taken in as food must be balanced to provide the amino acids needed to
produce the necessary proteins, muscles, enzymes, and so forth.
Enzymes contain accessory components necessary for function, that is, cofactors,
some of which are provided, either directly or indirectly, by vitamins and minerals.
Vitamins used by the body as accessory components for various processes are
shown in Tables 2.8 and 2.9. A lack of these important components of the diet can
lead to conditions that have been considered diseases in the past and present. Vitamins
are essential but also poisonous if present in too high a concentration. In addition some
enzymes contain minerals such as zinc, copper, and iron that are essential parts of the
mineral component of the diet. Thus enzymes are complex but essential components of
the body.
In addition to their importance in enzyme function, the minerals calcium and
phosphorus are used to build bones and teeth and are important in other structures
as well. Fiber plays no direct role in development or functioning of the body on
either the macro or cellular level; it is nevertheless extremely important to proper
function. Movement of food through the body is essential in that different food com-
ponents are digested and absorbed in different portions of the digestive tract. Also it is
important to move digested food out of the body if for no other reason than to allow
room for more food intake. A mixture of soluble and insoluble fibers works best for
carrying out the important functions of fiber in the diet.
In all cases the body manages its intake of essential nutrients in such a way as to
allow the individual to grow, survive, and reproduce before death. For this reason a lack
of the proper nutrition leads to a decrease in stature and, in extreme cases, a decrease in
mental facility. A basic reality is that deprivation at any time, particularly during the
