7. Fats
Fats, or fatty acids, are an
important macronutrient both for food intake and as a source of energy
when you are not eating and generating energy from
your own stored tissue. Fats are also important because they contain
fat-soluble vitamins such as A, D, E, and K, as well as other
nutrients.
Note
I use the mnemonic device “a deck of cards” to
remember the vitamins in fats: ADEK, or “a deck.” Not bad,
huh?
Many fat-containing foods also contain protein and/or carbs; in
fact, it’s quite common to get all three macronutrients in your
food.
We get our fats from a variety of foods, including dairy (e.g.,
butter, whole milk, cheese), veggies like avocados and olives, meat,
fish, nuts, coconut oil, nut butters, and oils (olive, peanut, coconut,
etc.).
The form in which fats are both stored and eaten is called a
triglyceride. This is an E-shaped molecule with a
glycerol backbone attached to three fatty acids, as Figure 10 depicts.
Note
The body also contains fats in the form of
phospholipids in cell membranes, cholesterol (which is crucial for
synthesizing steroid hormones and making vitamin D in the skin), and
other less substantial forms, but the vast majority of fat is stored
in lipocytes, or fat cells, in the body’s fat
depots such as adipose tissue and muscles.
Each one of the three fatty acids in a triglyceride is a
hydrocarbon chain (often just described as a chain of carbon atoms) that
is liberated at digestion and eventually released to the bloodstream. In
other words, after you consume an animal or a plant fat (veggies also
contain fats!), the simplified version is this: an enzyme called
pancreatic lipase splits up the triglyceride into
separate molecules, including the three fatty acids, so that they can be
absorbed in the small intestine (a triglyceride cannot be absorbed in
its present bulky state).
When the body stores fats, they are reassembled into
triglycerides, and when you metabolize fats for energy, they are split
up (yet again, just as in digestion) and are transported by proteins in
the form of free fatty acids (FFAs) in the blood. Somewhat similar to
the other macronutrients, the FFAs are the Lego pieces that can be fit
together into the triglyceride structures, along with the glycerol
molecule. Figure 11
shows an FFA called lauric acid, a shorter-chain fat with 12 carbons in
its chain.
Note
The body can store fats in a waterless environment,
and therefore they are a more efficient, lightweight storage medium
for a human’s onboard energy. We each store about 100,000 calories’
worth of fat. Carbohydrates have an affinity for water, on the other
hand, and therefore weigh more, including the water, as stored
glycogen. It would take about 67 pounds of stored glycogen to
represent the equivalent energy of 10 pounds of stored
fat!22 This
must be one of the reasons that we only store about 1,200 to 2,000
calories’ worth of glycogen, our own starch.
Free fatty acids have common names like lauric or stearic acid,
along with a numbered symbolic notation, such as 12:0. This means that
lauric acid, a saturated fat, has 12 carbon atoms and 0 double bonds
along its chain. Before your eyes glaze over with this reminder of geeky
Mr. Taylor’s Chem 101 class back in Wichita Falls, realize that the
length of a fatty acid chain is always even, and represents a good geek
detail for understanding fat nutrition. We promise!
A saturated fat (satFat, my abbreviation) is a molecule that has
a straight, noncurvy orientation (without the “kinks” or double bonds
of the other fats). This orientation allows the satFats to fit
together snugly and remain solid at room temperature (like cheese, or
butter, before they get moldy and rancid!). On the other hand, a
polyunsaturated fat (polyFat) has more than one
double bond along its carbon chain (which is where the
poly prefix comes from). This creates a bend, or
kink, in the molecule. That structural aspect keeps polyFats liquid at
room temperature.
A polyunsaturated fat that is much discussed for its health
benefits, an Omega 3, is called eicosapentaenoic acid (EPA).
Note
Forget it, don’t even try to pronounce
it.
EPA has a notation that looks like 20:5, n-3, indicating that
this fatty acid has 20 carbon atoms and 5 double bonds, and that the
first double bond is located three carbons in from the Omega end of
the chain (i.e., at the end of the “toes” of the E-shaped structure,
rather than at the location where the fatty acid chains connect with
the glycerol molecule).
Note
Only a food chemist really wants to practice
memorizing these complicated notations. You can impress your
friends, however, by calmly explaining to them the difference
between saturated and polyunsaturated fat; one’s
kinky!
A monounsaturated fat (monoFat), like the
oleic acid in olive oil, has only one double bond in the
molecule.
