Complete Book of Vitamins and Minerals

ISBN: 9780785305118

定价: 72.00

内容简介

that are vital for life. The proteins of muscles??? the hor-
mones??? the enzymes??? the fats??? and the stored forms of
sugar are examples of such necessary compounds. As a
result of these complex reactions??? chemical waste prod-
ucts are produced as well and must be eliminated from
the body. And??? of course??? all-important energy is either
stored or released as these reactions are taking place.
What is energy? Energy is simply the ability to do work.
Today we talk about the energy value of foods and about
the number of calories that a particular food provides.
The calorie is a unit of heat energy; that is??? it measures
energy as a form of heat. The energy value of individual
fbods depends on the amount of carbohydrates??? fats??? or
proteins present. Measured in calories per gram??? carbo-
hydrates and proteins supply four calories per gram???
and fats yield nine calories per gram. One gram is often
described as equal to the mass of a paper clip. And here
comes a mini-math lesson: There are 28.3 grams in an
ounce and 453 grams in a pound. A milligram (mg) is
1./1???000 of a gram; a microgram (pg) is 1/1???000???000 of a
gram??? or 1/1???000 of a milligram.
Different types of energy are interchangeable. For
example??? the chemical energy of carbohydrates??? which
are important body fuels??? can be converted into heat
energy to help maintain a constant body temperature. It
can also be changed to kinetic energy necessary for
muscle action and physical activity??? or it can be trapped
as chemical energy in other body compounds.
The Essential Nutrients
As the science of chemistry developed in the 18th and
19th centuries??? so did procedures to analyze what we
eat. Scientists soon discovered the great variety ot