Chapter 1 Introduction to Nutrition
When you were a child, you ate whatever your family offered—as long as it tasted good
to you! Now that you’re an adult, your food choices are influenced by lots of other
factors, like what your friends are eating, how much time or money you have, and even
what mood you’re in. You’re also exposed to lots of messages—at home, on campus,
on TV, and on the Internet—about foods that contribute to health or disease. These
messages, too, probably influence your food choices. In fact, your desire to eat more
healthfully might even be what prompted you to take this course!
So let’s begin by exploring the science of nutrition—what it is, why it’s important, and
how you can identify reliable sources of nutrition information.
Nutrition is the scientific study of food and how food nourishes your body and influences
your health. When you eat a healthful diet, you avoid nutrient-deficiency diseases and
reduce your risk for chronic diseases—such as obesity, heart disease, and type 2
diabetes—that have strong nutritional components.
Nutrition is such an important key to good health that improving America’s nutrition has
become a national priority. For three decades, the Office of Disease Prevention and
Health Promotion, part of the U.S. Department of Health and Human Services, has
included nutrition-related objectives in their health goals for Americans. In their current
report, called Healthy People 2020, “Nutrition and Weight Status” is an extensive topic
area.
Nutrition only came into its own as a science a little more than a century ago, when
scientists first realized that certain chemicals in food were essential to human growth,
functioning, and even our survival. We now call these essential chemicals nutrients. The
six types of nutrients found in foods are carbohydrates, fats, proteins, vitamins,
minerals, and water.
The nutrients that provide the energy your body uses to fuel its activities are the
macronutrients: carbohydrates, fats, and proteins. Carbohydrates and fats are the
primary energy sources for your body. Proteins can provide energy if needed, but
they’re not primarily a fuel source. Instead, proteins provide the building blocks for your
body’s tissues and functional chemicals. The energy in foods is measured in Calories
(or, technically speaking, kilocalories). We can say that the energy found in 1 gram of
carbohydrate or 1 gram of protein is equal to 4 Calories, whereas the energy in 1 gram
of fat is 9 Calories.
Vitamins and minerals don’t provide energy, so they don’t provide Calories. Still, they’re
absolutely essential for your body’s breakdown and use of the macronutrients. Vitamins
are organic compounds, meaning that they contain carbon, which is almost always
bonded to hydrogen. Minerals aren’t compounds at all. They’re inorganic units of matter,
such as magnesium and iron, that exist in the same fundamental form whether they’re in
soils or in your body.
By the way, the best way to meet your vitamin and mineral needs is by consuming them
in healthful foods and beverages, not pills. Vitamin and mineral supplements can help
complete a healthful diet, but shouldn’t replace it!
Water is the most immediate nutrient of all. Most of your body’s chemical reactions
involve water, so it’s critical to healthy functioning. Water also bathes the inside and
outside of your cells, helps maintain your body temperature, and acts as a lubricant and
protective cushion.
Now that you know what the nutrients are, you may be wondering how much of each
you should eat. The Dietary Reference Intakes (DRIs) are standards you can use to
figure out how much of each nutrient is healthful for people in your gender and age
group to consume each day. There are six DRIs:
• The Estimated Average Requirement (EAR) is the average daily intake level
estimated to meet the requirement of half the healthy individuals in a particular
group. The EAR isn’t important for guiding your food choices, but nutrition
scientists use it to calculate the Recommended Dietary Allowance or RDA, our
next DRI.
• The RDA is the average daily nutrient intake level that meets the requirements of
97-98% of healthy individuals in a particular group. You should aim for this
amount.
• The Adequate Intake (AI) is an average daily nutrient intake level assumed to be
adequate. It’s used when scientists can’t determine an RDA.
• The Tolerable Upper Intake Level (UL) is the highest average daily nutrient
intake level likely to pose no risk of adverse health effects. So avoid exceeding
the UL.
• The Estimated Energy Requirement (EER) is the average dietary energy intake
that is predicted to maintain energy balance—neither weight gain nor weight
loss—in a healthy person.
• Finally, the Acceptable Macronutrient Distribution Range (AMDR) is a range of
healthful macronutrient intake expressed as a percentage of total energy intake.
For instance, the AMDR for protein indicates that you should consume from 10%
to 35% of your daily Calorie intake as protein.
The DRIs are, of course, only one type of nutrition information available. In fact, many
people feel overwhelmed by the abundant and often conflicting nutrition-related advice
published every day. What constitutes valid, reliable evidence? To answer this question,
it helps to understand the scientific method, a standardized process for conducting
research used by scientists worldwide.
The steps in the scientific method are: observing a phenomenon; creating a hypothesis;
designing and conducting an experiment; and collecting and analyzing data that support
or refute the hypothesis. If the experiment yields data indicating that the hypothesis is
wrong, it’s rejected, and an alternative hypothesis may be proposed and tested. If the
data support the original hypothesis, then a conclusion is drawn. However, the
experiment must be repeatable. A scientific theory is proposed only after repeated
experiments have supported the hypothesis.
Not all research studies are experimental. Observational studies observe and analyze
situations already existing. For example, epidemiological studies assess relationships
between factors observed in large populations—such as a population’s diet and risk for
colon cancer. In contrast, clinical trials are tightly controlled experimental studies in
which an intervention is given to determine its effect. In a clinical trial of high quality,
researchers randomly assign study participants to intervention groups and control
groups, and neither the researchers nor the participants know who is getting the
treatment. This is referred to as a randomized double-blind trial. Members of the control
group in such studies may receive a placebo, an imitation treatment such as a sugar
pill.
When evaluating research studies, it’s important to consider whether a conflict of
interest exists; for instance, is the study funded by the manufacturer of the product
being evaluated? When surfing the Internet for nutrition information, check the
credentials, date, and address of websites. As you may know, sites with a “dot com”
extension are there to make a profit, so be on the lookout for quackery, the
misrepresentation of a product or service for financial gain. If a claim sounds too good
to be true, it probably is.
