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the difference btwn Saturated and Unsaturated fat

Monday, March 19, 2012

As promised in my last entry where I discussed some definitions of what we eat (minerals, vitamins, proteins, etc), I will now discuss in detail the science behind fat. I will also focus on the difference between saturated and unsaturated fat, something I'm sure we all read but we might not know what it means.

Fats, structurally, are chains of repeated units of fatty acids and glycerol that form a triglyceride structure. Fatty acids contain chains of carbon molecules with hydrogen and oxygen side groups. Honestly, to anyone who isn't a chemist, these details may seem unimportant. However, as you may have noticed, some fatty foods (oils, butter, etc) can either be solids or liquids are room temperature. This physical states are largely dependent upon the specific structure of the fat be observed (note: "fat" commonly refers to solids while "oil" refers to liquids but technically these are both "fats." When I say "fat" I mean the technical term unless otherwise specified).

Saturated vs. Unsaturated fats

Remember what I said about the fatty acid chains; they are chains of carbon atoms with side groups. Simple enough. However, these carbons can either be connect with one bond or two bonds. When all carbons in the chain are connected with a single bond, they results in "saturated fat" because the have the maximum about of hydrogen atoms possible (saturated with hydrogen). When the chain contains two carbons that are connects with a double bond, it results in "unsaturated fat" because it contains two fewer hydrogen atoms with the presence of the double bond (this is based in basic chemistry. all you must know is that carbon as 4 locations where it can bond). Both structures can be seen in the diagram above.

Have you ever wondered what "mono" or "poly" unsaturated fat means? Now with your knowledge of the structure of unsaturated fats, take a guess. That's right: "monounsaturated fats" contain just one double bond in their fatty acid chain while "polyunsaturated fats" contain several double bonds in one fatty acid chain.

So why do we care about saturated or unsaturated fats?

Due to their structure, their energetic properties are different. There are many chemical and physical interactions that are involved in the physical state of fats but the most important is its ability to "stack". When a fat has only single bonds, it is much easier for the chains to stack side by side (due to flexibility with in the chain). This means that saturate fat will more readily form a solid at higher temperatures. Butter is a solid at room temperature. Take a guess as to what type of fat butter is defined as. That right: saturated fat. Because of the chains close proximity (which forms stronger intermolecular bonds) and also because of the high amount of hydrogen atoms, saturated fat yields more energy during metabolism.

Now, unsaturated fat, due to the rigidity caused by its double bounds, cannot "stack" as easily. This means that unsaturated fat is a liquid at higher temperatures. Can you think of any fats that are liquid at room temperature? How about olive oil? vegetable oil? Both of these are unsaturated, and, due to their physical state (weaker molecular bonds) and their fewer hydrogen atoms, unsaturated fats yield less energy during metabolism.

So what does this all mean?

Essentially, both unsaturated fats and saturated fats are fine for your body. You might want to steer away from saturated fats because as they "yield" more energy that means you can "store" more energy as fat within your own body. Unsaturated fat is slightly more "healthy" for this reason so maybe consider swapping in olive oil where you used to use butter. However, the real cardiac culprit is something called "trans fats".

What is a "trans fat"?

Remember how I said that unsaturated fat cannot stack as easily and therefore is a liquid at room temperature? Well, scientists have discovered a way to force unsaturated fatty acids to stack in a process called "hydrogenation." This is actually a chemical reaction used for many applications not related to fat.

To give you some background, imagine a wooden plank (this will represent the two carbons attached by a double bond). You have two really small nails (these will represent the hydrogen atoms) and two chains with a nail at the end to attach to the plank (these will represent the rest of the fatty acid chain). You can hammer the small nails on the same face and the two chains on the other face or you can hammer one small nail and one chain one each face (knowing at each end of the plank there must be one nail and one chain).

The first configuration is called "cis," meaning "same side" in chemistry lingo. The second configuration is called "trans," meaning "opposite sides." Unsaturated fat naturally forms in the cis conformation making awkward "kinks" in the chain that makes it difficult to stack. However, through this hydrogenation reaction, we can force the double bonds to take on a "trans" conformation with makes it easier for the whole chain to stack and therefore become a solid at room temperature. This is a trans fat. Both configurations can be seen in the image above.

To be honest, I am not sure why trans fats were ever invented. I'm guessing that scientists thought the lower caloric content of unsaturated oils but in a solid would be appealing, hence the invention of margarine (this is a trans fat) but we now know that trans fats increase the risk of coronary heart disease.

Aaaah, so much information! Why do we need fat in the first place???

Yes, yes, I know. Why not avoid fat all together if its so dang complicated? Well, having a certain amount of fat in your body is important for maintaining healthy skin, hair, and other cells as well as providing insulation against shock and extreme temperature. Fat also protects your vital organs from being attacked by various types of diseases or harmful chemicals. And of course, fat is just stored energy! So fat provides energy for crucial bodily functions that take place.

Phew! well, I'm tired just writing this all because there is a lot of basic chemistry involved. I may have skipped over a couple concepts for simplicity purposes, but, please, if you have any questions or want clarification, ask away!

Next time, I will start a series of blogs explaining the importance of specific vitamins and minerals.
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Member Comments About This Blog Post
  • GTEYE2015
    I understand regarding trans fat increasing LDL cholesterol and I understand the issues regarding weight gain but what I am wondering is what makes trans fats bad beyond that regarding "build up"?

    Once it enters my body, it's no longer at room temperature and I assume would no longer be a solid. I am just wondering how exactly that correlates to blockages above and beyond other saturated fats?

    1237 days ago
    Wow I found your blog post in a search about fat, very good job getting so technical.
    1669 days ago
  • SRG1955LICK
    you show an incredible skill at explaining technical things in common sense, easily understood language.
    2254 days ago
    2260 days ago
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