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Chapter 23 Separation Techniques: Mechanical and Chemical Methods
are two basic types of metabolic reactions. The fi rst type is anabolism.
Anabolism is the bonding of nutrients to make new compounds. This
type of reaction absorbs or uses energy. An example is combining
amino acids to make enzymes. The second type of metabolism is
catabolism. Catabolism is the breaking down of compounds into smaller
parts. Catabolic reactions release energy. This energy is used for
physical activity. The energy is also used to build body tissue and
sustain involuntary activities, such as breathing.
Metabolism of Salts
When salt is consumed in the diet, it is catabolized into sodium
and chloride. Most sodium in the body is in the fl uid that surrounds
cells. Large levels of salt in the diet cause sodium levels to rise as
compared to potassium, which is inside the cells. A key function of
both sodium and potassium is to control the osmotic fl ow of substances
in and out of the body cells.
Higher intakes of salt in diets around the world have been
connected to higher rates of hypertension (high blood pressure). It is
believed that as sodium levels in the blood rise, the body pulls water
from the cells. This helps maintain a constant sodium concentration
in the blood. However, the additional water in the blood increases
the total volume of blood. This causes a rise in blood pressure.
Hypertension is a problem for about 10% to 15% of the population.
Most people can successfully excrete excess sodium from the diet. Their
blood pressure and salt concentrations remain stable. Hypertension
appears to be caused by high sodium intakes combined with a faulty
ability to remove sodium through the kidneys.
Another problem with a high-salt diet is that it increases the body’s
need for water. If insuffi cient water is consumed, water is pulled from
the cells to maintain the correct salt concentrations. This puts stress
on the cells, reduces water availability for metabolism,
and could reduce overall health. See 23-11.
Metabolism and Water
Most metabolic reactions involve the release of or
use of water. Water is also the solvent for all metabolic
reactions within the cells. When there is insuffi cient
water, reactions slow. Energy is released at a lower
rate. Remember that water must be present before
carbohydrates, lipids, and proteins can be converted to
energy. Water is the solvent that transports nutrients
into the cell. It also transports waste products out
through the cell membrane. Any separation or
movement of compounds through cell membranes
requires water.
© Krysztof Slusarczyk/Shutterstock
23-11 A variety of salt-free seasonings,
spices, and herbs can be used to fl avor foods
without adding sodium to the diet.