Nutrition and Metabolism
Some dietary supplements are natural substances that
function as drugs in the human body. Proceed with caution!
Dietary calcium decreases the risk of
osteoporosis (see Clinical Application 7.2 on
page 204).
A low-fat diet lowers the risk of some cancers.
A diet low in saturated fat and cholesterol
lowers the risk of coronary heart disease.
Fiber, fruits and vegetables, and whole grains
reduce the risk of some cancers and coronary
heart disease.
Lowering sodium intake lowers blood
Folic acid lowers the risk of neural tube defects.
isplayed prominently among
the standard vitamin and min-
eral preparations in the phar-
macy or health food store is a dizzying
collection of products (±
g. 18B). Some
obviously come from organisms (bee
pollen and shark cartilage), some have
chemical names (glucosamine with
chondroitin, see chapter 8 vignette on
page 261) and some names are histori-
cal or cultural (St. John’s Wort). These
“dietary supplements” are neither food
nor drug, but they contain active com-
pounds that may function as pharma-
ceuticals in the human body.
By law dietary supplements
include: “a product (other than
tobacco) that is intended to supple-
ment the diet that bears or contains
one or more of the following dietary
ingredients: a vitamin, a mineral, an
herb or other botanical, an amino
acid, a dietary substance for use
by man to supplement the diet by
increasing the total daily intake, or a
concentrate, metabolite, constituent,
extract, or combinations of these ingredients.”
Labels cannot claim that a dietary supple-
ment diagnoses, prevents, mitigates, treats, or
cures any speci±
c disease. Instead, the language
is positive. For example, Valerian root “promotes
restful sleep” and echinacea and goldenseal
“may help support the immune system.” In 2004,
the U.S. Food and Drug Administration relaxed
requirements that evidence back up claims of
cure or prevention. It allows the following speci±
food and health claims:
Many dietary supplements
contain pharmaceutical agents, so
a physician should be consulted
before using these products, par-
ticularly if a person has a serious
illness or is taking medication. The
active ingredients in supplements
may interact with other drugs. For
example, the active ingredient in St.
John’s Wort, hypericin, lowers blood
levels of nearly half of all prescrip-
tion drugs by interfering with liver
enzymes that metabolize many
drugs. Some patients have experi-
enced intracranial hemorrhage after
taking ginkgo biloba, a tree extract
reported to enhance memory.
Certain dietary supplements
are of dubious value. For example,
the marketing of shark cartilage fol-
lowed initial studies that suggested
sharks do not get cancer. Sharks
have cartilaginous skeletons, so
the idea arose that their cartilage
somehow protects against cancer.
It turned out that sharks indeed
get cancer, and shark cartilage has no magical
properties. Similarly, pyruvic acid and ATP are
not necessary to boost energy levels—these
biochemicals are abundant in the cellular res-
piration pathways. Some health-food stores
sell DNA, merely expensive brewer’s yeast, and
unnecessary, because any food consisting of
cells is packed with DNA. The list is long of sup-
plements with little scienti±
c evidence of value,
yet dietary supplements are a multi-billion dol-
lar industry. Buyer beware!
Dietary Supplements—Proceed with Caution
of people have starved to death. Starvation is also seen in
hunger strikers, in prisoners of concentration camps, and in
sufferers of psychological eating disorders such as
Whatever the cause, the starving human body begins to
digest itself. After only one day without eating, the body’s
reserves of sugar and starch are gone. Next, the body extracts
energy from fat and then from muscle protein. By the third
day, hunger ceases as the body uses energy from fat reserves.
Gradually, metabolism slows to conserve energy, blood pres-
sure drops, the pulse slows, and chills set in. Skin becomes
dry and hair falls out as the proteins in these structures are
For example, a person who secretes insuf±
cient bile salts is
likely to develop a de±
ciency of fat-soluble vitamins because
bile salts promote absorption of fats. Likewise, severe and
prolonged emotional stress may lead to secondary malnutri-
tion, because stress can change hormonal concentrations in
ways that break down amino acids or excrete nutrients.
A healthy human can stay alive for 50 to 70 days without
food. In prehistoric times, this margin allowed survival dur-
ing seasonal famines. In some areas of Africa today, famine
is not a seasonal event but a constant condition, and millions
previous page 755 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 757 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off