Nutrition Education

Testing Your Nutrition Knowledge: Lipids – Part 1

Okay, so as a nutrition major, you kind of love biochemistry… or is that still only me?

Anyways, I’m in the process of reviewing some basic nutrition biochemistry. It’s important to keep this information in tip-top shape as a nutrition student, but let’s be honest. Some of this stuff escapes us sometimes. So here I am, preparing an intro-level biochemistry break down of one of our major macro-nutrients: lipids (AKA: fat).

This information isn’t only beneficial for nutrition students to review, but as a regular health-conscious individual, too. Now you’re asking, what’s so important about understanding basic lipid biochemistry? Well, have you ever read a nutrition facts label and notice the Total Fat section? Did you freak out when you saw how much fat was in the product? But, did you look at the subheadings? You know, the Saturated/Trans Fat and occasionally Mono-/Polyunsaturated Fat sections? This is important! You know when people say “good fats” and “bad fats”? This is what they’re talking about, and it does make the difference in your fat intake! (Okay, yes I am biased. You can definitely get away with not getting into the biochemistry, but where’s the fun in that?! …Still just me?) Anyway, I’ve composed this handy blog to hopefully shed some light on the macro that society seems to love and hate.

Lipids Basics

Lipids can be broken down into 4 classes:

  1. Triglycerides (AKA: triacylglycerols)
  2. Phospholipids
  3. Sterols (Yes, cholesterol is a lipid, believe it or not.)
  4. Lipoproteins

For this blog, we are going to focus solely on triglycerides, as this is the form that we mainly consume and store in our body.

What’s the importance of triglycerides?

  • Stored fat protects our organs (known as visceral fat).
  • Stored fat also helps keep us warm! (primarily subcutaneous fat – this is the reason why individuals with anorexia nervosa grow thin hair on their body, known as lanugo, in an attempt to keep their body insulated).
  • It allows our body to store energy for starvation states.
  • It helps with the storage/bioavailability of fat soluble vitamins (Vitamins A,D,E,K).

The structure of a triglyceride is also quite simple, as it’s pretty much explained in the name. Tri = 3 (fatty acids) and glyceride = the glycerol backbone.

Triglyceride Structure
Figure 1. Triglyceride chemical structure. Photo source: http://study.com/cimages/multimages/16/triglycerides2.jpg
Triglyceride
Figure 2. Simplified triglyceride structure. Photo source: http://pbsg.npolar.no/website-images/fatty-fig1.GIF

The fatty acids are bound to the glycerol backbone with what is known as an ester bond. 

What are fatty acids? They’re basically a hydrocarbon chain (hydrogen and carbon) with a carboxyl end (the COOH end; AKA: delta or alpha end) and a methyl end (the CH3 end; AKA: the omega end). This is how all fatty acids are alike: they all contain, carbon, hydrogen and oxygen and have a carboxyl and methyl end. However, fatty acids can (and do) differ in many ways.

1.They can differ in the length of the chain.

Length meaning the number of carbons in the hydrocarbon chain. Refer to Figure 1. Note that the cut-off points for the following tend to differ depending on different sources.

  • Short: <8 carbons in length
  • Medium: 8 – 14 carbons in length
  • Long: >14 carbons in length

2. They can differ in the number of double bonds.

Double bonds refers to the bonds between the carbons. When a double bond exists, it is denoted with a double line between the carbons. Simply put, a double bond is when a hydrogen is removed from the normal bond, causing a double bond to form between the two carbons. (Chemistry crash course: carbons like to have 4 bonds. In a regular bond in a fatty acid, one carbon is bonded to 2 carbons and 2 hydrogens – it’s a happy carbon. When a hydrogen is removed, central carbon will get lonely and form a second bond with one of the carbons next to him, who also lost a hydrogen. Happy carbons unite. Two hydrogens were lost in the making of this double bond).

  • No double bonds: Saturated fat (as in, the fatty acid is saturated with hydrogens).
  • One double bond: Mono-unsaturated fat (AKA: MUFA)
  • Two or more double bonds: Poly-unsaturated fat (AKA: PUFA)

Double bonds are important in fatty acids, because this determines the physical properties of the fat. A double bond causes a kink in the structure of a fatty acid. This kink prevents tight binding of fatty acids together, which results in the fat being liquid at room temperature. For analogy, think of a dozen pencils. Since they are all straight, they can pack together easily. Now say someone breaks all of your pencils so they make right angles. These pencils don’t pack together so well, do they? The same principle applies to fatty acids.

For instance, vegetable oils are rich in poly-unsaturated fats. Remember, poly-unsaturated means several double bonds are present. The more double bonds, the more kinks, the harder it is to pack these fatty acids together. Hence, the liquid state of vegetable oils.

Saturated vs. Unsaturated
Figure 3. Saturated vs. Unsaturated fatty acids. Notice how the double bond creates a kink in the structure of the fatty acid. Photo source: https://courses.washington.edu/conj/membrane/fattyacid.png

3. They can differ in the type of double bond.

  • Cis: A fancy way to say that the two hydrogens that make up the double bond are on the same side. Cis is the natural form of a double bond. The hydrogens on the same side is what forms the kink in structure, and allows for liquid physical property.
  • Trans: This means that the two hydrogens are on opposite sides. This is what industry makes through the process of partial hydrogenation (we’ll talk a little bit about that later). When hydrogens are on opposite sides, this removes the kink in the structure, and allows for a straight fatty acid. Thus, a solid fat physical property results. Industry-made trans fat are basically the dregs of the fat world. Stay away from the trans fats at all costs, my friends (I’ll get to that, too).
Cis vs. Trans
Figure 4. Cis vs. Trans fatty acids. Notice the hydrogens on opposite sides allow for a straight fatty acid. Photo source: http://katherineau.com/wp/wp-content/uploads/2015/07/trans-fatty-acid.jpg

4. They can differ in the location of the double bonds.

  • Omega 3s: These are poly-unsaturated fatty acids with their first double bond located at carbon number 3 from the methyl (CH3/omega) end.
  • Omega 6s: These are poly-unsaturated fatty acids with their first double bond located at carbon number 6 from the methyl (CH3/omega) end.
Omega 3 vs. Omega 6
Figure 5. Omega 3 vs. Omega 6 fatty acids. Notice that the first double bond for omega 6 occurs at carbon number 6 from the CH3 (methyl/omega) end, and the first double bond for omega 3 occurs at carbon number 3 from the CH3 (methyl/omega) end. Photo source: http://natural.getprograde.com/images/article_images/polyunsaturated_images_sm.png

Getting this far, I realize this can be a lot of information to understand, and honestly, this blog is kinda getting too long… So, look for Part 2, where we will discuss the food sources of these different types of fats and the health implications of each! (That’s the good stuff, folks).

Happy biochemistry-ing! 🙂

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s