Download Module 4 – CARBOHYDRATES

Module 4 – CARBOHYDRATES
Objectives:
Define carbohydrate.
List the monosaccharides.
List the disaccharides.
List the polysaccharides.
Define fiber.
Describe carbohydrate digestion.
Explain lactose intolerance.
Carbohydrates can be found in foods of all shapes, sizes, colors and flavors. They
breakdown into the sugar glucose, which in turn allow us to chase a soccer ball, run from
the bad guys, twiddle our thumbs and most importantly use our brains. Poor
carbohydrates. They seem to have gotten their unfair share of negative publicity lately.
In fact, some would say carbohydrates, or “carbs”, as they are often called, are just plain
bad for you.
In this module we will exam what a carbohydrate is and the role carbs play in your body.
You will learn how the body digests, absorbs and utilizes carbohydrates? We will also
explore why some carbohydrates are necessary for good health, while other carbs should
be avoided?
What is a carbohydrate?
Carbohydrates are one of the six nutrients. You will recall from Module 1, they
contribute 4 kcals per gram. The word carbohydrate comes from the words “carbon” and
“hydrate” (meaning water or H2O). Carbohydrates are made up of carbon-C, hydrogenH and oxygen-O molecules. This occurs as the result of good old Photosynthesis.
Remember that from high school Biology? Green plants make different carbohydrate
sugar molecules via photosynthesis. From this point forward, you may see carbohydrates
abbreviated as CHO, meaning carbon, hydrogen and oxygen.
Two molecules of hydrogen and one molecule of oxygen, also known as, H2O, or
water, come from the ground up through the root of a plant.
H–O–H
Carbon and oxygen, also known as, CO2, or carbon dioxide are absorbed into the
leaves of a plant.
C–O–O
Glucose is the main carbohydrate made by plants. Plants use glucose to fuel the work
they are meant to do. In some ways, plants are a busy as people. They too have jobs to
do. Some make fruit while others make nuts, seeds or berries. When animals consume
plants, they get fuel from the plant, so their muscles can do work.
Carbohydrates are the first link in the food chain. Think about it. Fish eat plant life,
animals eat plant life and humans eat plant life. Even the most ferocious meat-eating
carnivore is likely to prey on an animal that is in part a plant eater. Carbohydrate food
sources are almost always at their very basic level…plants. Well, with one exception –
there always seems to be an exception – Milk. Milk is the only animal product that
contains carbohydrates. More on this later.
Carbohydrates are sometimes referred to as ‘sugars”. Words ending in “ose” generally
denote the term “sugar”. There are six important “sugar” molecules in nutrition.
The first three sugar molecules are referred to as single sugars, or one sugar molecule.
Single sugars are referred to as Monosaccharides. The prefix “mono” means “one”.
You might recall the board game Monopoly. Generally, the winner was the “one” person
who owned all the real estate.
MONOSACCHARIDES
1.
Fructose –
This is the sugar that makes fruit sweet. Fructose is found in
fruit, honey and table sugar.
2.
Glucose –
This sugar is found in both plant and animal cells. It is also
sometime referred to as blood sugar.
Galactose –
This is the sugar, or carbohydrate that we find in milk and milk
products. Remember, it is the only carbohydrate that is animal
based, not plant based.
All carbohydrates are made up of 6 carbons, 12 hydrogen and 6
oxygen molecules.
The difference between the 3 monosaccharide molecules above
is how they are configured.
DISACCHARIDES
The remaining three sugar molecules are referred to as double sugars. The term “di”
means “two”. Here you will find that the disaccharides are made up of two connecting
monosaccharides.
4.
Sucrose -
This sugar is made up of both a unit of
glucose + fructose
5.
Maltose -
This sugar is made up of two units of
glucose + glucose
6.
Lactose -
This sugar is made up of both a unit of
glucose + galactose
ENZYMES
The monosaccharides (glucose – fructose – galactose) are absorbed right into the blood
stream during digestion. The disaccharides however, must first be broken down into their
individual monosaccharide units before the body can use them. This process requires the
work of various enzymes. Generally, words that end in “ase” refer to enzymes. The
enzymes required to split our disaccharides down to monosaccharides are:
Sucrase
splits
Sucrose
into
Fructose + Glucose
Maltase
splits
Maltose
into
Glucose + Glucose
Lactase
splits
Lactose
into
Glucose + Galactose
Once these double sugars, or disaccharides are broken down into their individual
monosaccharide units, they are ready to absorbed into the bloodstream and used as
energy by the body. Glucose will provide immediate energy to the cells that need them.
Fructose and galactose first will need to make a pit stop at the liver, so they can get repackaged into glucose. Ultimately, all these different sugars, eventually become glucose,
which your body can use for energy…and that is a good thing…unless you eat too much.
The mono- and disaccharides make up what are sometimes referred to as simple sugars.
When we consume simple sugars the process by which they are broken down, absorbed
into the bloodstream and then used by the body is a very quick and efficient process.
This is great if you’re about to pass out due to a lack of food, or low blood sugar, but can
wreak havoc for people trying to lose weight, or who have diabetes.
POLYSACCHARIDES
Polysaccharides are also referred to as complex carbohydrates. The prefix “poly”
means “many”. The word polyester for example means many synthetic fibers. The word
polysaccharide means many sugar molecules. A polysaccharide is composed of many
glucose molecule units. There are three major polysaccharides.
1. STARCH
Starches are composed of many long strands
of glucose units. The starch amylose looks more like a strand of pearls while the
starch amylopectin is slightly more branched. Because the glucose strands are
shorter on amylopectin, due to their branching, it is much easier to break them down.
It is much easier to break down and digest a starch once it has been cooked vs.
consuming it raw. Think about eating raw pasta, raw rice or a raw potato. Hmmm.
Not very appetizing is it?
Raw Starch → Resists digestion
Cooked Starch → Highly digestible
Remember…Starch is the storage form of glucose in plants.
2. GLYCOGEN
Glycogen is a very highly branched polysaccharide.
Suppose you suddenly need to run from the bad guys. Your body can start pulling
glucose from all of these little branches so you have lots of energy to fight, struggle,
breath hard, or run away…fast! Glycogen is generally stored in our muscle tissue and
liver. It serves as the body’s fuel tank. When blood sugar levels drop, you can turn
your glycogen into glucose and this happens all the time. The flip side though is if
your body’s fuel tanks (glycogen stores) are full and you have extra glucose, your
body will instead covert this extra glucose into…FAT.
Remember…Glycogen is the storage form of glucose in animal
tissue.
3. FIBER
Fiber is an indigestible polysaccharide. The bonds that hold fibrous glucose units
together are different than the bonds that hold starch and glycogen glucose units
together. Therefore, the body can’t digest them and as a result they also can’t
contribute any calories to your diet. There are two main types of fiber.
A. Soluble Fiber – Soluble fiber will dissolve in water and is easily
fermented by the bacteria in your colon. This can produce undesirable
and embarrassing odors.
That would be the downside. The good
news about soluble fiber is that they can help lower your risk of heart
disease and diabetes, by lowering your blood cholesterol and slowing
glucose absorption. Soluble fiber food sources include, barley, oats,
oat bran, rye, fruits (apples, citrus), legumes, seaweeds and seeds.
B. Insoluble Fiber – Insoluble fiber will not dissolve in water and is does not
ferment in your colon☺ Its primary contribution to the body is to
increase the weight and transit time of feces moving through the colon.
By providing bulk and a feeling of fullness, it may contribute to
weight management. Insoluble fiber foods sources include, brown
rice, fruits, legumes, seeds, vegetables, wheat grains and wheat bran.
Remember…Most adults should get 20 – 35 grams of dietary fiber
daily.
Use the table below to help you identify fiber sources in your favorite foods.
ACTIVITY:
Go to the grocery store. Sticking with the same brand name of bread, select a loaf of
100% whole wheat bread and compare it to their white bread label. Use the following
criterion in your comparison.
Serving size
Calories per serving
Calories from fat
Grams of carbohydrate
Grams of sugars
Grams of fiber
Grams of protein
Note the first five ingredients listed.
Note any large discrepancies you notice in vitamin/mineral content.
Note the price per loaf.
Which bread do you feel is more nutrient dense? Why?
CARBOHYDRATE DIGESTION
It is important to understand how carbohydrates are digested and absorbed by the
body, so diseases like hypoglycemia, diabetes and lactose intolerance can be better
managed. It can also be extremely helpful to athletes as they develop their workouts
and prepare for competition.
As we discuss CHO digestion, it is worth reviewing what you have already learned.
Disaccharides (sucrose, maltose and lactose) will breakdown into
monosaccharides (glucose, fructose and galactose).
Glucose will get absorbed directly into the blood stream where it
can be used for immediate energy.
Fructose and galactose, once absorbed into the bloodstream will
need to stop off at the liver, so they can be converted into glucose.
Starch will also breakdown into individual glucose molecules and
they too will be used for energy.
Glycogen is found in animal products, but since the breakdown of
glycogen occur very quickly after the animal dies it is not involved
in food consumption.
Fiber is indigestible. It does not provide energy, because it does
not contribute any calories.
DIGESTION – From Carbohydrate to Glucose
Carbohydrate digestion begins in the mouth. As you chew, saliva is
secreted, along with the enzyme amylase. If you’ve ever detected the sweetening of
bread in your mouth as you chewed, it was likely due to the maltose in starch
breaking down into glucose.
As food is swallowed and reaches the stomach, digestion is halted. Glucose
however, can get absorbed into the bloodstream at this point by passing through the
wall of the stomach.
Most CHO digestion takes place in the small intestines. As CHO’s are emptied from
the stomach into the small intestines the pancreas will secrete the enzyme
pancreatic amylase to continue the digestion of starch. Additionally, the enzymes
maltase, sucrase, and lactase are also secreted by the pancreas to start breaking the
disaccharides down into monosaccharide molecules.
Once CHO digestion is complete, you are left with glucose, galactose and fructose.
Remember, only glucose is ready for instant energy – galactose and fructose will
head for the liver where they will be re-packaged and shipped out as glucose.
Now, all the starch, di- and monosaccharide molecules should be out of your GI
(gastrointestinal) tract and busy being used by a cell somewhere in your body, or they
are being re-packaged as glycogen where they can be used for energy later, or…they
are being converted into FAT. Getting this balance right…is really the crux of
weight management…to be continued in a later module.
We’re still not quite done with CHO digestion. We can’t forget Fiber. Because fiber
doesn’t get digested, it continues traveling through the intestines until it reaches the
colon or large intestines. Unfortunately, it is here that bacteria feed on the fiber
causing fermentation to occur, which can produce gas and odors.
entire process occurs within 1 – 4 hours after consuming a meal.
This
The image below shows how carbohydrates in food become glucose
in the body.
LACTOSE INTOLERANCE
Have you ever wondered why milk, cheese or ice cream, just doesn’t seem to “agree”
with you? It may be that you are lactose intolerant. You may experience bloating, gas,
or abdominal pain after consuming such foods. Lactose intolerance occurs in
individuals who do not produce enough lactase to break the disaccharide lactose into its
two monosaccharide molecules, glucose and galactose. Lactose alone is simply too big
to move through the border of the small intestines into the bloodstream. It needs the
enzyme lactase to break it down. When no lactase is present, lactose will simply
continue on down into the colon (large intestines). Here, as with fiber, the bacteria in the
colon will feed on the lactose allowing fermentation to occur, thereby producing gas,
bloating, diarrhea, cramping and abdominal pain. The condition itself is not serious, but
the symptoms can be embarrassing and uncomfortable. Approximately, 75% of the
world’s population suffers from lactose intolerance.
Milk and milk products are excellent sources of calcium, vitamin A and vitamin D.
Individuals who are lactose intolerant are advised to seek out “lactose-free” milk, like
Lactaid®, consume fortified soy milk products, or try lactase enzyme caplets.
It is also important to know that lactose intolerance is not a milk allergy. A milk
allergy occurs when your body attacks the main protein in milk (casein). Lactose
intolerance occurs due to a lack of the enzyme lactase. See, one has to do with the
protein in milk – the other has to do with the carbohydrate in milk.
Remember…Lactose Intolerance is not a milk allergy.
Whole wheat bread, brown rice, pasta, vegetables and fruits are all examples of
carbohydrate rich foods. Cookies, brownies, chips, crackers and sodas are also examples
of carbohydrate rich foods. The later are mostly made up of simple sugars that digest
very quickly. They give us immediate glucose energy and then we “crash” and feel
hungry again very quickly. More complex carbohydrates like whole grains, vegetables
and some fruits digest much slower. We get our energy from glucose eventually, but feel
fuller longer and maintain a more level blood sugar concentration…so we snack less.
If you are trying to lose weight, think about giving up the carbohydrates that offer empty
calories and keep the healthier, complex carbohydrates in your diet. Glucose is the
preferred fuel for body functions and they brain uses glucose almost exclusively! Now
that’s something to think about.
QUIZ
1. The monosaccharides include:
a.)
sucrose, maltose, lactose
b.)
fructose, glucose, galactose
c.)
glucose, maltose, lactose
d.)
fructose, glucose, lactose
2. The disaccharides include:
a.)
sucrose, maltose, lactose
b.)
fructose, glucose, galactose
c.)
glucose, maltose, lactose
d.)
fructose, glucose, lactose
3. The polysaccharides include:
a.)
starch, fiber, glucose
b.)
starch, fiber, galactose
c.)
starch, fiber, glycogen
d.)
fiber, glycogen, lactose
4. Which of the following is not an enzyme used for carbohydrate digestion:
a.)
lactose
b.)
lactase
c.)
sucrase
d.)
amylase
5. Foods rich in soluble fiber help lower cholesterol.
a.)
b.)
true
false
6. Lactose intolerance is a milk allergy.
a.)
true
b.)
false
7. Around the world, most people are lactose intolerant.
a.)
true
b.)
false
8. __________ and ___________ are converted to glucose in the liver.
a.)
glucose, lactose
b.)
glucose, fructose
c.)
glucose, galactose
d.)
fructose, galactose
9. Carbohydrates are made up of the following molecules.
a.)
carbon, hydrogen, oxygen
b.)
carbon, hydrogen, water
c.)
carbon, water, nitrogen
d.)
hydrogen, water, glucose
10. Milk is the only animal source of carbohydrate.
a.)
true
b.)
false