Types of Lipids
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There are three types of lipids in the body, triglycerides, phospholipids and sterols.
Triglycerides are also known as triacylglycerols and compose 95% of fat in the foods we eat. Triglycerides are also the main fats we store in our body. When you pinch an inch around your waist, you are pinching triglycerides. Phospholipids bring water and fat together and are called emulsifiers. Phospholipids make up cell membranes and lipid carrier molecules. Sterols are found in tissues of animals and plants. The most well known sterol in our body is cholesterol. Cholesterol makes up bile, hormones and vitamin D. |
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Triglycerides (fats)
Fat is just one type of lipid and an abbreviation for fatty acids. Three fatty acids attach to glycerol to create a triglycerides, also called triacylglycerol. Phospholipids and sterols are not fats. Sterols are lipids and triglycerides are lipids, but cholesterol is not a fat. Calling cholesterol a fat is like calling a Californian, a Texan. Both Californian and Texans are Americans, but Texans are not Californians, and Californians are not Texans.
Saturated fatty acid structure
Saturated, mono and polyunsaturated fatty acids
Saturated fats are solid at room temperature, examples are butter, coconut oil and animal fat. The highlighted purple structure in the image to the right represents a saturated fat. This structure is simply a bunch of carbons joined together (carbons are not shown) and they are saturated with hydrogen. A carbon has four places to form a bond and in a saturated fat, a carbon will join with another carbon on either side. That fills up two spots, this leaves two free. When the fatty acid is fully saturated, this means hydrogen takes up those other spots. A fully saturated fatty acid is solid at room temperature. It is more stable.
Double bond: carbon in blue and hydrogen in purple
To understand this concept better, look at the illustration to the left. In the top image, carbon is shown in blue and there are four bonding points for each carbon. Notice how the carbons are bonded to each other and the remaining three bonding spots are taken up by hydrogen. The carbons are fully saturated with hydrogen.
Now look at the lower image, carbon has four bonding spots, but two spots are taken by the double bond between the carbons. This means the carbons only have two spots left to bond hydrogen. These carbons are not fully saturated and in a fatty acid, would be termed unsaturated. Fatty acids with double bonds are less stable than those that are fully saturated.
Now look at the lower image, carbon has four bonding spots, but two spots are taken by the double bond between the carbons. This means the carbons only have two spots left to bond hydrogen. These carbons are not fully saturated and in a fatty acid, would be termed unsaturated. Fatty acids with double bonds are less stable than those that are fully saturated.
Monounsaturated fatty acid structure
Look back to the image of the three types of fatty acids. The highlighted olive green structure in the image above is a monounsaturated fatty acid. A monounsaturated fat (MUFAs) is a fatty acid with one point of unsaturation. Mono means one. What this means is that there is one double bond. In the image, the double bond is represented by two parallel lines. It's called a point of unsaturation because these two carbons are not fully saturated with hydrogen. The carbons are double bonded to each other.
Polyunsaturated fatty acid structure
Polyunsaturated fatty acid (PUFAs) means that there's more than one double bond. This means that there is more than one point of unsaturation. Polyunsaturated fatty acids are named by their first point of unsaturation. If you look back up at the fatty acid image, the polyunsaturated fatty acid is represented in blue. For example, alpha linolenic acid has double bonds at the 9th, 12th and 15th carbons and the chemical name is 9,12,15-octadecatrienoic acid.
Fatty Acids in Oils
Unsaturated fats and this includes monounsaturated fatty acids and polyunsaturated fatty acids, are liquid at room temperature, examples are olive oil and canola oil. Omega-3 and omega-6 fatty acids, our essential fatty acids, are polyunsaturated fatty acids. The first double bond starts at the 3rd carbon in omega-3 fatty acids and the first double bond starts at the 6th carbon in omega-6 fatty acids.
Different oils have different compositions of various fatty acids. You might hear that olive oil is all monounsaturated fatty acids and canola oil is made up of omega-3 fatty acids (PUFAs). The reality is, most foods contain a variety of both saturated and unsaturated fatty acids. Both monounsaturated fats and polyunsaturated fats, omega-3 fatty acids and omega-6 fatty acids.
In the chart below, the blue represents a saturated fatty acid. Red is a monounsaturated fatty acid. Omega-6 fatty acids are represented by green and omega-3 fatty acids by purple. Omega-6 and omega-3 fatty acids are polyunsaturated fatty acids. Take a look at flaxseed oil, you can see that flaxseed is mostly composed of omega-3 fatty acids, but still contain a fair amount of monounsaturated fatty acids shown in red and small amounts of omega-6 fatty acids and saturated fatty acids. Corn oil is mostly omega-6 fatty acids shown in green, but also has saturated and monounsaturated fatty acids and a tiny bit of omega-3 fatty acids. Olive oil is known for being a good source of monounsaturated fatty acids, shown in red, but notice that olive oil has small amounts of the other fatty acids as well. Lastly, take a look at coconut oil, known to be higher in saturated fatty acids, shown in blue. There are small amounts of monounsaturated fatty acids and omega-6 fatty acids, but no omega-3 fatty acids. Understanding that foods contain multiple types of fatty acids is important. For example individuals will consume walnuts when hearing that they are a good source of omega-3 fatty acids, but walnuts actually have 4 times as much omega-6 fatty acid as they do omega-3 fatty acids.
Different oils have different compositions of various fatty acids. You might hear that olive oil is all monounsaturated fatty acids and canola oil is made up of omega-3 fatty acids (PUFAs). The reality is, most foods contain a variety of both saturated and unsaturated fatty acids. Both monounsaturated fats and polyunsaturated fats, omega-3 fatty acids and omega-6 fatty acids.
In the chart below, the blue represents a saturated fatty acid. Red is a monounsaturated fatty acid. Omega-6 fatty acids are represented by green and omega-3 fatty acids by purple. Omega-6 and omega-3 fatty acids are polyunsaturated fatty acids. Take a look at flaxseed oil, you can see that flaxseed is mostly composed of omega-3 fatty acids, but still contain a fair amount of monounsaturated fatty acids shown in red and small amounts of omega-6 fatty acids and saturated fatty acids. Corn oil is mostly omega-6 fatty acids shown in green, but also has saturated and monounsaturated fatty acids and a tiny bit of omega-3 fatty acids. Olive oil is known for being a good source of monounsaturated fatty acids, shown in red, but notice that olive oil has small amounts of the other fatty acids as well. Lastly, take a look at coconut oil, known to be higher in saturated fatty acids, shown in blue. There are small amounts of monounsaturated fatty acids and omega-6 fatty acids, but no omega-3 fatty acids. Understanding that foods contain multiple types of fatty acids is important. For example individuals will consume walnuts when hearing that they are a good source of omega-3 fatty acids, but walnuts actually have 4 times as much omega-6 fatty acid as they do omega-3 fatty acids.
Sterols
The most common sterol in the body is cholesterol. Most people think of cholesterol as just being bad for health, but cholesterol is essential for life. But, it's not essential to our diet because the body can make cholesterol. Cholesterol is part of our cell membranes and nerve sheaths. We make bile from cholesterol and our steroid hormones are made from cholesterol. Vitamin D starts as a cholesterol in your skin which is activated by UV light. Below is diagram of cholesterol as an integral part of the cell membrane.
Cholesterol as part of the cell membrane
Phospholipids
Phospholipids are emulsifiers, they have the ability to bring water and fat together, two substances which normally do not combine. An example is lecithin. The next time you're at the grocery store pick up a salad dressing and you will most likely see lecithin in the ingredient list. In the body, phospholipid act as a lipid bilayer in the cell membrane. Most cells will have some sort of phospholipid membrane.
Categories and Functions of Lipids Video
References
- Sizer, F. Whitney E. The Lipids: Fats, Oils, Phospholipids and Sterols. In: Nutrition Concepts and Controversies. 13 ed. Belmont, CA: Wadsworth. 2014.
- National Nutrient Database for Standard Reference Release 28. The National Agricultural Library. United State Department of Agriculture. Last accessed April 2, 2016.
- Cholesterol illustration by Dhatfield on Wikimedia Commons, CC BY-SA 3.0.
- Saturated fatty acids by Calvero, polyunsaturated fatty acid by Edgar181, monounsaturated fatty acid, all in the public domain.
- Carbon double bond image created by Christine Dobrowolski, CC BY-NC-SA 2.0.
- Fatty acid chart created by Christine Dobrowolski using the National Nutrient Database for Standard Reference, CC BY-NC-SA 2.0.
Last updated April 6, 2016