Mini Lesson: Fats

Video Transcript

Structure of Fats

Fats are a considered macronutrients since our bodies needs quite a bit compared to vitamins and minerals. The most basic form—the fatty acid—is a group of molecules on one end that form a sort of head, attached to a tail of carbon and hydrogen molecules. These fatty acids behave differently depending on how long the tail is and how many hydrogens there are for each carbon molecule. 

Shorter chain fatty acids can actually mix with water, while those with a longer chain will not. As for the hydrogen bonds, when every possible bonding site on a carbon is filled with a hydrogen, we refer to this as a saturated fatty acid.  The tail structure is straight, allowing multiple fatty acids to fit neatly together. A monounsaturated fatty acid has one location along the tail where two carbon molecules are double-bonded to each other rather than having all bonding sites filled with hydrogen. This creates a kink in the tail structure so these fatty acids do not fit so neatly together. Polyunsaturated fatty acids have multiple sites where carbons are double-bonded, creating a multi-kinked tail structure. And though not technically a fat, cholesterol is a lipid structure that is generally grouped with fats because it does not mix with water.

Digestion of Fats

To be absorbed, fatty acids need to be separated from triglycerides, cholesterol, or phospholipids. This happens when fat specific enzymes release the fatty acid from the cholesterol or glycerol molecule joining it as a triglyceride or phospholipid. These enzymes are found to some extent in the mouth and the stomach, but more fat digestion happens in the small intestine because the bile released from the liver and gallbladder will break apart larger droplets of fat so that the fat-specific enzymes from the pancreas can get to all the fatty acids and release them.

Absorption of Fats

Fatty acids are absorbed fairly easily. The tricky part is making sure they can get through the watery environment inside the small intestine to the cells where they can be absorbed. Since shorter chain fatty acids can mix with water, short and medium chain fats can be freely taken in by the small intestine cells and then passed to the blood vessels on the other side of the cell to be taken to the liver.  

However, long chain fatty acids, cholesterol, and fat soluble vitamins do not mix with water, so getting them to the cell for absorption takes a little extra effort. After helping to break down fat droplets, bile also helps to combine these larger molecules into a micelle that transports them to the cells where they can be absorbed. This also means these molecules cannot be freely transported in the blood either, so the small intestine cells regroup them into chylomicrons that will transport them through the body. But the chylomicron is too large for the small blood vessels that carry nutrients away from the small intestine, so the chylomicrons are transported by the lymphatic system from the small intestine to the vein just blow the collar bone where the lymph is mixed with the blood before it is pumped through the body.

Function of Fats in the Body

These fats can be used to provide a source of energy in the body, but they are also used to make the walls for cells and organelles, and some can also form molecules that either increase or reduce inflammation in the body. Cholesterol is used to make hormones and the bile that carries toxins out of the body and helps in fat digestion.

Food Sources of Fats

When we consider the fat content of a food, we often consider how many saturated and unsaturated fats there are. There are no foods that contain only saturated, monounsaturated, or polyunsaturated fats, because all foods will have some mixture of all of these types of fats.  However, we often categorize a food based on which type of fatty acid is most abundant.

Because saturated fats fit neatly together, they tend to be solid at room temperature, such as in the case of coconut oil, butter, and other animal fats. Monounsaturated fats are liquid at room temperature, but solidify when refrigerated, as can be seen with olive and avocado oils, and are also found in some nuts and seeds. Polyunsaturated fats will typically stay liquid even when refrigerated and are found in fish, nuts, seeds, and the oils from those foods.

Importance of Fats

Fats are not just a source of calories in the diet, but play many important roles in the body. Choosing to eat foods with a balance of different healthy fats supports important hormones in the body, regulation of inflammation, and healthy cell structure and growth.