Fat is one of the most misunderstood and vilified substances in all of nutritional science. I’d like to spend the next few days getting to the bottom (no pun intended, haha) of why we need fat, what kinds we need, and why fat has gotten such a bum (wow, two puns in one sentence!) rap. Today, let’s go over what some terms commonly used to describe fat actually mean. It may not be the sexiest thing you’ll ever read, but it will help you gain a better understanding of nutrition in general.
Fat is one of three primary macronutrients (along with protein and carbohydrates), meaning it is something we consume in large amounts to provide the body with bulk energy.
Think way back to high school chemistry for a minute. Fat is an organic compound, which means it is made of carbon atoms. These carbon atoms form chains, and the available bonds in those chains are filled with hydrogen atoms. These molecules (made up of the carbon and hydrogen atoms) are called fatty acids. Most fat in our bodies and in the food we eat is made up of three fatty acids bonded to a glycerol molecule. [This forms a triglyceride - see how the name makes sense? Look for more discussion about these when cover lipid theory. Exciting stuff!]
Fatty acids are classified by either saturation or length. Today we’ll discuss saturation.
Saturated fats are the easiest to understand. When a fat is saturated, it means all available carbon bonds are occupied by a hydrogen atom. Each of the carbon atoms making up the fatty acid are completely filled – or saturated – with a hydrogen atom. Makes sense, right?
The structure of saturated fats makes them highly stable. They do not normally go rancid or get damaged by heating. They are also generally solid (or semi-solid) at room temperature as they have a straight structure that packs easily together.
Examples of saturated fats are animals fats (such as lard or tallow) and the tropical oils (such as coconut or palm).
OK, generally we don’t call any fats just unsaturated fats. But I want to explain the idea that there are fats that are NOT saturated with hydrogen atoms. They are lacking these hydrogen atoms because some of the carbon atoms have formed double bonds (to each other). How many of these double-bonds a fatty acid contains determines whether it is monounsaturated or polyunsaturated.
Mono, of course, means one. Monounsaturated fats contain one double bond where carbon atoms have bonded together (and have therefore each missed bonding with hydrogen atoms). Where the double bond occurs, the molecule tends to bend. This means that unlike the molecules in saturated fats, those in monounsaturated fats don’t line up quite as nicely, making these fats liquid at room temperature (although they become more solid at colder temperatures).
An example of a monounsaturated fat is oleic acid, the main component of olive oil, along with some nut oils and avocado oil.
We’re almost to the finish line now!
With poly meaning many, you have probably guessed that polyunsaturated fats have many (two or more) pairs of double bonds. These fatty acids have kinks or turns at the positions of the double bonds and do not fit together nicely. They are therefore liquid, even when refrigerated. Because of the unpaired electron at the double bond (just take my word for that part) they are highly reactive. Polyunsaturated oils go rancid easily, and should not be heated or used in cooking.
One last note on polyunsaturated fatty acids: When found in nature, both the hydrogen atoms and the double bond are on the same side. This is called the cis form. Tuck that under your hat for a future discussion.
Essential Fatty Acids (EFAs)
The two polyunsaturated fatty acids found most commonly in our food are:
- Double unsaturated linoleic acid, containing TWO double bonds. These are also called Omega-6 fatty acids.
- Triple unsaturated linolenic acid. These contain THREE double bonds and are also called Omega-3 fatty acids. (These are particularly prone to rancidity.)
[By the way, the "6" and "3," respectively, refer to the position of the first double bond.]
Unlike saturated and monounsaturated fatty acids, which your body can produce, your body cannot make these polyunsaturated fatty acids. They are therefore called essential fatty acids and must be obtained from the food we eat. (We’ll also go further into these at another time.)
How it All Fits Together
The fact is that actually, ALL fats, whether from animal or vegetable sources, contain a combination of saturated fatty acids, monounsaturated fatty acids, linoleic acid and linolenic acid. The preponderance of one over the other (for instance, coconut oil is 92% saturated fat) determines its classification.
And now that you know all of this, you are one step further on your journey to making informed decisions for yourself and your family. Knowledge is power! Make sure to stay with us as we continue getting the skinny on fats.
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