Download Chapter 3 – The Carbohydrates: Sugar, Starch, and Fiber

Chapter 3 – The Carbohydrates: Sugar, Starch, and Fiber
Chapter 3 Summary
The Body’s Need for Carbohydrates
The primary role of carbohydrates is to provide energy for the body. In fact, the brain and nervous
system rely almost exclusively on carbohydrates (in the form of blood glucose) for their energy needs.
Since the body cannot manufacture carbohydrates, they must be supplied through the diet. Additionally,
carbohydrates contribute to certain body structures. Therefore, carbohydrates are essential to life.
Carbohydrates Basics
The primary role of carbohydrates is to provide the body with energy (calories), and for certain body
systems (for example, the brain and the nervous system), carbohydrates are the preferred energy source.
At least half our food energy is derived from carbohydrate, principally from starch but also from the
simple sugars. Carbohydrates are classified as complex carbohydrates or simple carbohydrates. Although
carbohydrate bashing is a popular pastime, it is excess calories that are fattening. If you are in the habit of
serving carbohydrate-rich foods laden with fat, it is the fat, not the carbohydrate, that raises the calorie
count the most.
The Simple Carbohydrates
The most common of the single sugars is glucose; the sweetest, fructose. Galactose is the third. Each of the
three double sugars (sucrose, lactose, and maltose) contains a molecule of glucose paired with fructose,
galactose, or another glucose. Sucrose or table sugar contains both glucose and fructose. The source of
energy from concentrated sweets such as sodas, cakes, and candy is sucrose. Lactose, or milk sugar, is
made up of a molecule each of glucose and galactose. Lactose is easily digested except by people with
lactose intolerance. The third double sugar, maltose, is made up of two molecules of glucose.
We are encouraged to use the concentrated sweets – the so-called empty-calorie foods—only in
moderation, so as not to displace needed nutrients. The same does not apply to the naturally occurring
sugars found in fruits and dairy products.
The Complex Carbohydrates: Starch
The polysaccharides starch, glycogen, and fiber are composed of chains of glucose units. Starch is the
storage form of glucose in the plant. Sources of starch in the diet include seed, grains, and starchy
vegetables. Dietary fiber is indigestible by humans.
The Complex Carbohydrates: Fiber
Researchers note the beneficial effects of both insoluble and soluble fibers in the diet for reducing the risk
of diseases such as atherosclerosis, colon cancer, diabetes, diverticulosis, and obesity. It is important to
eat a variety of high-fiber foods to reap the benefits derived from both types of fiber.
Guidelines for Choosing Carbohydrates in the Diet
It is recommended that people consume 45-65% of their total calories from carbohydrates, preferably
from complex carbohydrates such as whole grains. USDA’s MyPyramid provides a framework from
which to select carbohydrates in the diet.
How the Body Handles Carbohydrates
Nutrition status affects our well-being even at the level of the body’s cells. The body strives to maintain
its blood glucose within a normal range for optimal health and functioning. The hormones insulin and
glucagons function to maintain normal blood glucose levels in the body. Glycogen is made in the liver
and muscles from excess glucose in the bloodstream. It can be broken down by the liver to maintain a
constant blood glucose level.
Sugar and Health
Many misconceptions about sugar (simple/refined sweeteners) abound. Perhaps the biggest problem
with sugar is that it is an “empty-calorie” food. That is, it contains calories and virtually nothing else. If a
person consumes a lot of sugar, it may certainly crowd out other nutrient-dense foods, or may contribute
to the over-consumption of total calories and therefore obesity. Additionally, sugar has been linked to
increases in dental carries (cavities). A judicious diet includes some simple sweeteners, but no more than
10% of total calories (hopefully).
Sweet Talk—Alternatives to Sugar
This chapter’s Spotlight feature answers questions regarding the many artificial and alternative
sweeteners available on the market today. The artificial sweeteners are nonnutritive sugar replacements
such as aspartame, saccharin, and sucralose. The alternative sweeteners contain and include fructose and
the sugar alcohols – including sorbitol and xylitol. The FDA authorizes use of the health claim on food
labels that sugar alcohols do not promote tooth decay.