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Carbohydrates
Carbohydrates are an essential nutrient. You will learn how to classify carbohydrates and the
names for the most common sugar units in food. You will also learn the recommended intakes
and acceptable macronutrient distribution ranges for fiber, carbohydrates, and refined and
added sugars. Answer the following questions in the space provided using the models and
information provided in this handout. You may use your textbook as an additional resource. Be
sure to divide tasks evenly and according to the roles you were assigned in your group (i.e.
recorder, manager, fact checker). Be prepared to share and discuss your answers with the class.
Carbohydrates are classified into two distinct groups: simple and complex.
Let’s focus on simple carbohydrates first. We have two kinds of simple sugars: monosaccharides and
disaccharides. The three sugars you see below are the monosaccharides: fructose, glucose, and
galactose. Glucose is the only sugar the body uses.
Model 1: The three monosaccharides
1. These sugars are made from only three elements of the periodic table. Name them.
To make disaccharides, two of these three monosaccharides are paired up. Below are three of the most
common disaccharides.
Model 2: Common Disaccahrides
Almost all carbohydrate-rich foods come exclusively from the plant kingdom, with the exception of
lactose.
2. In which animal food and its products can you commonly find the disaccharide lactose?
It may surprise you to know that not all sugars have the same sweetening power. Fructose is 1.5 times
sweeter than glucose, which is why it is so popular in the food industry as an added sugar. Added sugars
or “refined sugars” should be limited in use. When simple sugars are eaten from a whole food such as an
apple, that apple is also providing fiber and various phytochemicals, vitamins, and minerals to the body.
An apple is a nutrient-dense food. On the other hand, refined and added sugars provide only calories
and very few (if any!) nutrients. We call these foods “junk foods” or “empty-calorie foods”.
Added sugars should be less than 25% of your daily calorie intake.
Complex carbohydrates are made from monosaccharide building blocks. Complex carbohydrates are
simply chains of thousands of monosaccharides together. There can be different monosaccharides in a
chain or there can be only one kind. Let’s look at three complex carbohydrates which are all made out of
only the monosaccharide glucose: fiber, starch, and glycogen.
Fiber
Starch
Model 3: Fiber, Starch, and Glycogen
3. What is the difference between these three complex carbohydrates?
Glycogen
Glycogen is found in animals exclusively and is not considered a food source for human, but we do take
the extra glucose in our blood and store it as glycogen in the liver and muscles. The difference between
liver and muscle glycogen is that the liver releases its glycogen store into the general blood circulation so
any tissue, for example the brain, can use it. The muscles keep their glycogen for the specific muscle in
which it is stored.
4. Compare the mass of the liver versus the mass of muscle in the body. Which of the two do you
think will store more glycogen? Why?
Fiber is also called cellulose. Cellulose is what makes up the structure of plant cells and is responsible for
the bulk of what you chew when you eat leafy vegetables such as spinach. Humans don’t have the
enzyme responsible for breaking down fiber, and as a result we are unable to digest it and absorb it. We
get no energy from fiber, only bulk.
5. Based on what you have just read, how many calories would you hypothesize that fiber has?
Although we get no energy from fiber we still a Daily Recommended Intake (DRI) of fiber that we should
eat because fiber provides bulk to push digested food and then waste through our digestive tract. For
every 100 calories consumed you need to eat 1.4g of fiber.
6. Give two examples of fiber-rich foods.
7. The average American eats about 2,700 calories a day and about 15g of fiber.
a. Do the math to determine if this is too little or too much fiber?
b. Give two examples of what could be contributing to this excess or deficiency in fiber in
the American population.
Starch is found in fruits, vegetables, and grains. Fruits, vegetables and whole grains also contain fiber.
Grains, fruits, and vegetables are considered nutrient-dense foods because they provide many nutrients
for few calories. Beans are also rich in carbohydrates.
With the exception of fiber, all edible carbohydrates provide us with energy. Every gram of carbohydrate
has 4 calories. This means if you ate 10 grams of saltines, you would have consumed 40 calories.
1 gram carbohydrate = 4 calories or 4 calories/gram carbohydrate
No matter what myths you may have heard, the consumption carbohydrate is essential! If the human
body eats less that 130g of carbohydrates a day it will go into ketosis. We will talk about ketosis later in
the semester, but just understand that we want to avoid being in ketosis. Glucose is the only energy
source that the brain and central nervous system uses under normal conditions.
Carbohydrates also have Accetable Macronutrient Distribution Ranges (AMDRs), and in fact,
carbohydrates make up the largest chunk of the AMDR percentages.
AMDRs
Carbohydrates
Protein
Fat
45-65%
10-35%
20-35%
8. Why should we eat more carbohydrates than any other macronutrient?
Created by Mary Puccini, MS, RD and Alexandra Castro (Supplemental Instructor), 2014