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Disorders of Nutritional Status
227
E, and K. They require dietary fat for absorption and
transport. The nine water-soluble vitamins are vitamin C
and the B vitamins, which are thiamine, riboflavin, niacin,
vitamin B
6
, pantothenic acid, vitamin B
12
, folate, and bio-
tin. Because excess amounts of the water-soluble vitamins
are excreted in the urine, it is less likely that they may
become toxic to the body, but the fat-soluble vitamins are
stored in adipose tissue and may reach toxic levels.
Minerals are inorganic elements, not compounds;
however, they often function as components of cer-
tain enzyme systems, vitamins, and hormones. They
are involved in energy metabolism, acid-base balance,
maintenance of normal hemoglobin levels, and play a
role in nervous system function, are involved in muscle
contraction and skeletal development and maintenance,
and are major components of bone tissue. Minerals that
are present in relatively large amounts in the body are
called
major minerals
. These include calcium, phospho-
rus, sodium, chloride, potassium, magnesium, and sul-
fur. The remainder are classified as
trace minerals
; they
include iron, manganese, copper, iodine, zinc, cobalt,
fluoride, chromium, molybdenum, and selenium.
Fiber
Fiber cannot be digested by the human gastrointestinal
system and is not classified as a nutrient; however, it
increases stool bulk and facilitates bowel movements.
Soluble fiber, the type that produces a gel in the intestinal
tract, binds with cholesterol and prevents it from being
absorbed by the body. Soluble fiber also lowers blood
glucose. More studies are needed to establish whether
fiber prevents colon cancer and promotes weight loss.
The adequate daily intake for fiber for adult men and
women up to age 50 is 38 and 25 g, respectively. Adults
over age 50 should consume 30 and 21 g, respectively,
each day. The recommendation for children ranges from
19 to 31 g, and the recommendation for teenagers is
similar to that for adults.
7
Regulation of Food Intake
Stability of body weight and composition over time
requires that energy intake matches energy utilization.
Environmental, cultural, genetic, and psychological fac-
tors all influence food intake and energy expenditure. In
addition, body weight is tightly controlled by various
physiologic feedback control systems that contribute to
the regulation of hunger and food intake.
Hunger, Appetite, and Satiety
Hunger and appetite are closely associated with food
intake. The sensation of
hunger
is associated with sev-
eral sensory perceptions, such as the rhythmic contrac-
tions of the stomach and that “empty feeling” in the
stomach that stimulates a person to seek food. A per-
son’s
appetite
is the desire for a particular type of food.
It is useful in helping the person determine the type of
food that is eaten.
Satiety
is the feeling of fullness or
decreased desire for food.
The hypothalamus contains the feeding center for
hunger and satiety
1
(Fig. 10-1). It receives neural input
from the gastrointestinal tract, which provides informa-
tion about stomach distention, chemical signals from
nutrients (glucose, amino acids, and fatty acids) in the
blood, and input from the cerebral cortex regarding the
smell, sight, and taste of the food. Centers in the hypo-
thalamus also control the secretion of several hormones
(e.g., thyroid and adrenocortical hormones) that regu-
late energy balance and metabolism.
Stomach
Vagus nerve
Large
intestine
Small
intestine
Fat cells
Pancreas
Leptin
Insulin
Ghrelin
Ghrelin
GLP-1
CCK
Hypothalamus
–
+
–
FIGURE 10-1.
Feedback mechanisms for control of food
intake. Black lines leading to − indicate feedback signals that
decrease appetite and feeding, and blue lines with + indicate
feedback signals that increase appetite and feeding. Stretch
receptors in the stomach activate sensory afferent vagal
pathways that inhibit food intake. Glucagon-like peptide-1
(GLP-1), cholecystokinin (CCK), and insulin are gastrointestinal
hormones that are released by the ingestion of food and
suppress further feeding. Ghrelin, which is released by
the stomach and small intestine, especially during fasting,
stimulates appetite. Leptin is a hormone produced by
increasing amounts of fat cells as they increase in size; it
inhibits food intake. (Modified from Guyton AC, Hall JE.
Textbook of Medical Physiology. 11th ed. Philadelphia, PA:
Elsevier Saunders; 2006:868.)
