Fats
In this section, you will learn how to distinguish from saturated, unsaturated, and trans fatty
acids. You will also learn the functions and structure of the three different kinds of lipids. Lastly,
we will see what he AMDR for fat is and compare it to that to the other macronutrients. Answer
the following questions in the space provided using the models and information provided in this
handout. You may use your online lecture notes and textbook for additional resources. 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.
Let’s start with a discussion on the structure of fatty acids, which are the building blocks for
triglycerides: the most abundant fat in food. You have probably heard about saturated and unsaturated
fats, but what does that mean exactly?
Saturated means that we have packed something as tightly as it can get and we cannot possibly add
anymore.
Unsaturated means that there is still room left over for us to fit more things in.
Olive Oil
Butter
Model 1: Olive Oil vs Butter
To the naked eye, unsaturated fats, such as olive oil, look liquid because the unsaturated fat molecules
are bent and pack together unevenly with a lot of space between them. This extra space between the
molecules is what makes the unsaturated fats liquid.
In contrast, saturated fat molecules are not bent. These molecules are one straight line and this allows
them to arrange themselves very tightly and close together. This lack of space between molecules is
responsible for saturated fats being solid at room temperature.
1. Based on what you just learned, will saturated fats be solid or liquid at room temperature?
Why?
2. Give two examples of unsaturated fats.
Chemically speaking, saturated fats just mean that the carbon chains are full of hydrogen, whereas in an
unsaturated fat, there is still the possibility of adding more hydrogen to the carbon chain.
Saturated fats should be limited to 7%-10% of total calories.
A saturated fat becomes unsaturated with the addition of a Carbon-Carbon double bond (this is what
causes the molecule to bend), as seen below. We name unsaturated fats by the number of carboncarbon double bonds they have. A fatty acid with one double bond is called a monounsaturated fatty
acid. Fatty acids with more than one carbon-carbon double bond are called polyunsaturated fatty acids.
Model 2: Saturated, Trans and Cis fats
A trans fat is an example of an unsaturated fat, but the carbon-carbon double bond has a different
direction that does not cause it to bend. Trans fats are made by taking an unsaturated fatty acid and
adding hydrogen to it. Even though trans fat molecules have a double bond and are made from
unsaturated fats, they end up looking an awful lot like saturated fat molecules. Look at the model below.
See how similar they look to saturated fat?
Model 3: Trans, Unsaturated, Saturated Fat Structure
Because they look so similar to saturated fat, the body does not differentiate between the two and as a
result, both trans and saturated fats end up raising your cholesterol levels.
If possible, you should avoid all trans fats, but if you do end up eating them, they should add up to no
more than 1% of your total calories.
Having said all this, you must be aware that all fats in food are a mixture of these different structures.
Olive oil, for example, has mostly unsaturated fats, but also has some saturated fatty acids. Since it has
mostly unsaturated fats, it stays liquid at room temperature. Butter has mostly saturated fats, but also
contains some unsaturated fatty acids. Since it was mostly saturated fats, it stays solid at room
temperature.
3. Using what you just learned, predict the type of fat that makes up most of the following foods
on the table
Saturated
Unsaturated
Trans
Canola Oil
Chicken Fat
Margarine (made from vegetable oils)
Almond Oil
Salmon Oil
We have talked about the structure of fatty acids, but there are two important fatty acids that you
should remember: Omega-3 and Omega-6 fatty acids. These two fatty acids are essential. They cannot
be made by the body.
Omega-3 fatty acids are beneficial in that they coat platelets trying to stick to artery walls and make it
difficult for plaques to form. Omega-3 fatty acids are also an integral part of the brain. We can find
Omega-3 fatty acids in cold water fish such as salmon. Most Americans don’t get the right ratio of this
fat, and so Omega-3 fatty acids should be stressed in the diet.
Omega-6 fatty acids are important for cell membrane structure. Most Americans get enough of this
essential fatty acid. Omega-6 fatty acids can be found abundantly in plant oils.
Model 4: Alpha-Linolenic and Linolenic acid
4. Based on the picture above of Omega-6 and Omega-3 fatty acids, would you say these two
essential fatty acids are monounsaturated or polyunsaturated? Explain your reasoning.
We talked about fatty acids; now let’s talk about lipids in general. There are three types of lipids and we
already mentioned one: triglycerides.
3 Fatty individual fatty acids
A glycerol molecule
Model 5: Triglyceride
It is composed of a glycerol backbone and 3 individual fatty acid chains like the ones we discussed
earlier. A triglyceride is the most common lipid found in foods and also the main type of lipid found in
our adipose (fat) cells.
Next, we have phospholipids.
Hydrophilic head: made of a choline
molecule with a Phosphate atom that is
not afraid of water.
Hydrophobic tails: made of 2 fatty
acids that don’t mix with water
Model 6: Phospholipid
Phospholipids come together to form what is called a “lipid bilayer”
which you probably know better as a cell membrane. In the body, this is
its single most important function.
Phospholipids also act as emulsifiers. Emulsifiers allow fats to travel in
watery solutions without coming together and forming a big puddle of
oil. Lecithin is an example of a phospholipid used as an emulsifier. Look
for it in the ingredients of your next salad dressing!
Model 7: Phospholipid Bilayer
Finally, we have sterols.
Sterols are structures made up of rings of carbon that make up a wide variety of body compounds.
Vitamin D, estrogen, testosterone, and progesterone, and various other hormones and compounds are
also sterols.
For our purposes, the most important of these sterols is cholesterol. Cholesterol is the major component
in plaque build-up in the arteries which lead to heart disease. It is also very important to have between
the lipid bilayer that we mentioned before so that the can have fluidity as it moves through the body.
Interestingly enough, you can also make vitamin D, bile, and sex hormones from cholesterol.
Cholesterol can be made by the liver from the saturated fatty acids in our diet, and is therefore not
necessary in our food. Cholesterol should be limited to 300mg a day if healthy. If you already have
high cholesterol, your cholesterol should be limited to 200mg a day.
Fats have the most energy out of all the macronutrients they have 9 calories per gram of fat.
Below are their corresponding AMDR percentages for all types of fat.
AMDRs
Carbohydrates
Protein
Fat
45-65%
10-35%
20-35%
5. Use the table below to summarize the major points of the three categories of lipids.
Lipid
Structure
Functions
Where is it
found?
Triglycerides
Phospholipids
Sterols
Created by Mary Puccini, MS, RD and Alexandra Castro (Supplemental Instructor), 2014
Example