A fat molecule, more formally known as triglyceride, is made up of a glycerol molecule and three (tri) fatty acid molecules. Fatty acids have a head made of carbon, hydrogen and two oxygen molecules. The tail is made up of repeating sequences of carbon and hydrogen. The carbon atoms line up in a zig-zag formation and hydrogen atoms (not shown in images) are attached to the carbon atoms. The tails can vary in length and structure, which allows for a wide variety of fat molecules.
The fatty acids on a fat molecule can come in three types: Saturated, Monounsaturated and Polyunsaturated. The unsaturated fats can come in two different configurations: Cis and Trans. The type of fat and the configuration can have a significant impact on the fat molecule’s shape. Mono and polyunsaturated fats have a double bond between two carbon atoms on the fatty acids that causes the molecule to bend at that point. A double bond means that the two carbon atoms share two pairs of electrons instead of just one. Unlike saturated fats, which only have more stable single bonds, double bonds provide a suitable place for chemical reactions to occur.
Monounsaturated fats have one double bond whereas polyunsaturated fats have two or more double bonds. Saturated fats have no double bonds between carbon atoms and are saturated with hydrogen atoms. The double bonds make unsaturated fats more likely to react with oxygen or other reactive compounds. This is why unsaturated fats can go rancid faster than saturated fats.
The Types of fats
Saturated fats are fats that have no double bonds between their carbon atoms so they are saturated with hydrogen atoms. In this form, the fatty acid is relatively stable. This means that the molecule is less likely to react with other atoms or molecules and break down. It also has a uniform shape and charge that allows them to “stick” to other saturated fats. This stickiness causes them to be solid at room temperature. Only when the temperature is raised, usually above body temperature, (with some exceptions) will these fats become liquid. Example: Fat from a hamburger coming off a grill is a clear liquid. As that liquid cools down, it becomes a solid white fat.
Monounsaturated fats contain one double bond between two carbon atoms. The double bond prevents the atoms there from rotating freely like the rest of carbon atoms that are single bonded. As a result, it causes the fatty acid to bend at that point. Notice that the image of oleic acid above has one bend in it.
These fats have two or more double bonds in the fatty acid chain that causes the molecule to bend multiple times. EPA in the image above is a polyunsaturated fatty acid found in fish oil that contains multiple bends along its’ body.
Omega fats are polyunsaturated fatty acids. The omega refers to the first double bond that happens starting from the end of the fatty acid tail. For example, omega 3 fats have the first double bond occurring at the 3rd carbon from the end of the tail. Omega 6 fats have the first double bond at the 6th carbon from the tail.
DHA is an omega 3 fatty acid found in fish oil. Notice how the first double bond in the fatty acid occurs at the 3rd carbon from the omega (w) end. This is where the first bend in the molecule occurs.
Linoleic acid is an omega 6 fatty acid. Notice how the first bend occurs at the 6th carbon atom from the omega (w) end. This is where the first bend in the molecule occurs.
Cis and Trans fats
Cis (Cis – “same”) and Trans (Trans – “Across”) fat molecules are the two configurations that unsaturated fatty acids contain. It only occurs in unsaturated fats because the cis or trans configurations happen around a double bond. Most fats in food are cis fatty acids.
Cis-unsaturated fats have a boat-like shape. Notice how the hydrogen atoms (H) are on the same side of the two carbon (C) atoms that they’re bonded to. The Methyl groups (CH3) are also on the same sides as well. This shape prevents these fats from stacking together neatly, which is important because fatty acids that don’t stack neatly are liquid at room temperature.
Olive oil is a great example of cis-unsaturated fatty acids. All of the fats found in olive oil are cis-unsaturated fats so the oil remains as a liquid at room temperature. The temperature has to cool down significantly in order to allow the fats to stack well enough to become solid.
Trans fats are a monounsaturated fat. These fats can occur naturally in animal products like milk. We can, however, create trans fats by hydrogenising (adding hydrogen) to unsaturated fats. This process usually turns an unsaturated fat into a saturated one. However, some of these fats undergo a different transformation and become trans fats. These fats are very unhealthy fats and this is primarily due to their shape.
Oleic acid is monounsaturated fat that is found abundantly in foods like sunflower oil, safflower oil and peanuts. It has the chemical formula (C9H17C9H17O2) When this fat is hydrogenated, it can create an isomer (Iso – “equal”, mer – “parts”) called elaidic acid, which is a trans fat and has the exact same chemical formula as oleic acid. This “twin” of oleic acid does not have the same health benefits. The location of the double bond in both molecules really accentuates the boat and chair shapes of cis and trans fatty acids.
Remember, that cis fatty acids have a boat like shape. Trans fatty acids, on the other hand, are shaped like a chair. As you can imagine, boats don’t stack together so well. However, chairs do. Trans fats stack together very well. This allows trans fats to remain solid even when they are in your body.
There are other molecular forces in play that prevent cis-fats from stacking together as neatly as trans fats but the boat and chair structures are the most important factors. Enzymes help us break down (or build up) molecules in our body. Much like a lock and key, enzymes recognize specific molecules by their shape. Our bodies are equipped with the right enzymes to handle cis-fatty acids but not well equipped to handle trans fatty acids. When we eat foods that contain trans fatty acids, especially processed foods that contain unnaturally high amounts, they can build up in our arteries over time eventually creating a blockage. So, avoid trans fats as much as possible.
Avoiding Trans Fats
Unfortunately, the food industry has effectively lobbied the government, making it easier to get hazardous fats like trans fats into foods. Food manufacturers like saturated fats because they are more stable than unsaturated fats and allow foods to last longer on shelves without going rancid. In foods, this ingredient is usually listed as a ”partially hydrogenated” oil.
Food manufacturers are required to list the amounts of fat in their product. However, the manufacturers are not required to list the amount of fat per serving (or per bottle, per package…) if it is less than 0.5 grams per serving. It might seem like a small amount, but trans fats can stay in your body for a long time. On top of that, food manufacturers (and the government) see no need to keep you informed about the presence of this very unhealthy fat. Trans fats in any amount will end up raising your risks of heart attacks, stroke and atherosclerosis (hardening of the arteries) along with a host of other heart and brain related diseases. So, avoid processed foods, especially foods that have “partially hydrogenated” oils as an ingredient.
Rule Breakers: Healthy Saturated Fats
As mentioned earlier, saturated fats are solid at room temperature because their shape allows them to stack together easily. Like trans fats, many saturated fats will also stay solid in your body. For example, shortening (like Crisco) has a melting point of approximately 117 degrees, which is much warmer than your body can generate.
Some saturated fats, however, do not follow the rules. Medium chain fatty acids are saturated fats that are only 6 to 12 carbon atoms long. Other saturated fats like palmitic acid, which is a saturated fat commonly found in meat, is 16 carbons long and is a white solid at room temperature. Coconut oil contains plenty of medium chain fatty acids. The oil will remain as a solid until the temperature warms to about 76 degrees. At this point, it becomes a clear liquid instead of a white solid. Medium chain fats do not stick to each other as well as larger saturated fats. When the temperature is warm enough, the molecules move too fast to stick together causing them to become liquid. On top of that, Coconut oil does not go rancid for a long time, which is characteristic of the stable nature of saturated fats. Read more about the health benefits of Coconut oil and other foods with medium chain fatty acids in Part 2.
So, to sum it up, fats can come in saturated and unsaturated forms. Unsaturated fats can be in a cis or trans fat form and cis fats are healthier than trans fats. Polyunsaturated fats are also omega fats, which can have many health benefits. Read more about omega fats here. Not all saturated fats are unhealthy fats. Medium chain fatty acids, like lauric acid, stay as a liquid in your body. Our bodies also process medium chain fats differently, using them immediately as an energy source instead of storing it.