Download Chapter 7 – Water and the Minerals

Chapter 7 – Water and the Minerals
Chapter 7 Summary
Water—The Most Essential Nutrient
Water in the body participates in many chemical reactions and serves as a solvent, transportation
medium, lubricant, and regulator of body temperature. Water is by far the nutrient most needed by the
body. Water makes up part of every cell, tissue, and organ in the body and accounts for about 60% of
body weight. Inside the body, water performs many tasks vital to life.
The Major Minerals
Like the vitamins, minerals do not themselves contribute energy to the diet. Most minerals have diverse
functions within the body and work with enzymes to facilitate chemical reactions. Minerals are inorganic
compounds that occur naturally in the Earth’s crust, and most minerals are required in the diet in very
small amounts. Each of the major food groups supplies a number of minerals. The minerals are
traditionally divided into two large classes: the major minerals and the trace minerals.
About 99% of the body’s calcium is a structural component of the bones and teeth. The 1% of calcium
found in body fluids is essential for transmission of nerve impulses, muscle contraction, cell membrane
integrity, and blood clotting. A deficit of calcium during the growing years and in adulthood contributes
to adult bone loss and osteoporosis.
Phosphorus is so abundant in foods that deficiencies are unlikely. It participates with calcium in forming
the crystals of bone and therefore is found in large quantities in the body. Sulfur is present in all proteins
and is a constituent of body tissues. Skin, hair, and nails contain some of the body’s more rigid proteins,
and these have a high sulfur content. Magnesium plays a role in the synthesis of body proteins and thus
is important to all body functions; it also helps to relax muscles after contraction. A dietary deficiency of
magnesium is not likely, but may occur as a result of vomiting, diarrhea, alcohol abuse, or protein
malnutrition.
Special conditions are needed to regulate the amounts of water inside and outside the cells so that the
cells do not collapse from water leaving them or swell up under the stress of too much water entering
them. Sodium, potassium, and chloride are examples of electrolytes—dissolved substances in blood and
body fluids that influence the distribution of fluids among the various body compartments.
Sodium is abundant in the diet, as part of salt. Deficiencies are rare except in dehydration. Chloride,
which occurs in salt, contributes to the formation of the stomach’s hydrochloric acid. Potassium is
primarily involved in the working of nerve and muscle cells and is critical to maintaining the heartbeat.
The Trace Minerals
The trace minerals occur in the body in minute quantities and are needed in smaller amounts in the daily
diet.
Iron is the body’s oxygen carrier. Bound into the protein hemoglobin in the red blood cells, it helps
transport oxygen from lungs to tissues and so permits the release of energy from fuels to do the cells’
work. When the iron supply is too low, iron-deficiency anemia occurs. Meats, fish, and poultry are good
sources of iron. Whole-grain or enriched breads and cereals and legumes also provide dietary iron. Iron
absorption from plant sources can be enhanced by vitamin C and other factors.
Zinc is found in every cell of the body and plays a major role with more than 50 enzymes that regulate
cell multiplication, normal growth and sexual development, and metabolism. The richest food sources of
zinc include shellfish, meat, and liver. Milk, eggs, and whole-grain products are also good sources.
Iodine forms part of the thyroid hormones; deficiency may cause goiter, slowed metabolism, and
cretinism. The use of iodized salt protects against deficiency. The fluoride ion combines with calcium and
phosphorus to stabilize the crystalline structure of bones and teeth. Copper is important for red blood cell
formation, manufacturing collagen, and central nervous system function. Chromium works with the
hormone insulin in promoting glucose uptake into the cells and normal carbohydrate metabolism.
Selenium acts as cofactor for an antioxidant enzyme. Manganese and molybdenum function as part of
several enzyme systems.
Diet and Blood Pressure—The Salt Shaker and Beyond
The Nutrition Action feature discusses the causes, treatment, and prevention of hypertension. If you
would like to reduce your risk of developing high blood pressure, you can do so by:
 Adopting an eating pattern rich in fruits, vegetables, legumes, and low-fat dairy products—similar to
the DASH diet;
 Maintaining a healthy weight;
 Keeping sodium intake at or below recommended levels;
 Pursuing an active daily lifestyle;
 Drinking in moderation, if at all;
 Not smoking.
Osteoporosis—The Silent Stalker of the Bones
The chapter’s Spotlight provides an overview of osteoporosis and its risk factors and offers strategies for
preventing the debilitating effects of osteoporosis. Although bones undergo remodeling throughout life,
the total amount of bone mass in the human body reaches a peak by about age 30. Afterward, bones lose
strength and density as bone minerals are lost. To build bone mass and lower risk for osteoporosis:
 Maximize peak bone mass; consume the recommended amount of calcium (and vitamin D) for your
age.
 Consume alcohol only in moderation, if at all, and avoid cigarettes all together.
 Exercise regularly, since exercise can reduce the risk of developing osteoporosis by making bones
stronger and increasing their ability to absorb calcium.