Understanding Fats

Understanding Triglycerides

The fats and oils we find in foods are composed of triglycerides. You've probably heard someone talk about having a high level of triglycerides on a blood test; that simply means they have high levels of fat in their blood.

Triglycerides are composed of three fatty acids attached to one molecule of glycerine as shown on the right. When fats are digested, the bonds the fatty acids have with the glycerine are broken. That's the job of the lipase (fat-digesting) enzymes from the pancreas. The bile secreted from the liver has the purpose of making these fats water soluble so they can be absorbed and transported through the bloodstream.

The properties of various fats and oils (triglycerides) are determined by the type of fatty acids they contain. Fatty acids come in many varieties. They may be saturated or unsaturated. If they’re unsaturated they can be mono- or poly-unsaturated and the polyunsaturated fatty acids can be either the omega-3 or omega-6 type as shown in the chart on the left. They may also be long, medium, or short-chained. In the first part of this article, we'll explain what all of this means.

Saturated versus Unsaturated Fatty Acids

The fatty acids themselves are composed of long chains of carbon molecules that are bonded to hydrogen atoms. Something that helps me understand all this chemistry stuff is to think of various molecules as having differing numbers of hands which they can use to hold onto other molecules. Hydrogen has one hand. Oxygen has two hands. Carbon has four. So, each carbon atom can hold hands with the carbon in front of it and the carbon behind it. This leaves two free hands to hold onto two hydrogen atoms.

In the illustration above, the carbon atoms are red and the hydrogen atoms are blue. (The yellow ones are oxygen atoms that bond at one end of the chain.) You can see that each carbon atom is bonded to two hydrogen atoms, except for the final one, which is attached to three. The hydrogen atoms stick out sort of like Mickey Mouse ears. Because all of the carbons in the chain (not at the ends) are holding onto two hydrogen atoms the fatty acid pictured above is saturated.

If one or more pairs of carbon atoms are missing hydrogens, the fatty acid would be unsaturated. When the two carbons don't have a hydrogen atom to hold onto, they hold hands with each other, instead. This makes them double-bonded. In the illustration on the left, the double bond is highlighted in red.

Saturation affects the structure of the fatty acid. Saturated fatty acids are straight, while most unsaturated fats bend at the points where a carbon pair is missing hydrogen atoms. The bend makes the fat more fluid, which is why polyunsaturated fats tend to be liquid at room temperature, whereas saturated fats tend to be solid at room temperature.

This affects how they act in the body. Polyunsaturated fats help keep cell membranes pliable, while saturated fats make them stiffer. This influences the permeability of the membrane too. Too many saturated fats contribute to problems like insulin resistance.

The Omega Factor

Oils are Mixtures of Fatty Acids

The picture on the left shows three saturated fatty acids (arachidic, stearic, and palmitic) and two monounsaturated fatty acids (erucic and oleic). It also shows three polyunsaturated fatty acids (arachidonic, linoleic, and linolenic).

Fats are a mixture of all three types of fatty acids, in varying proportions. For example, coconut oil is 92% saturated, 6% monounsaturated, and 2% polyunsaturated fatty acids. Olive oil, on the other hand, is considered a monounsaturated fat because it is 15% saturated, 73% monounsaturated, and 12% polyunsaturated fatty acids. Safflower oil is a polyunsaturated fat because it is 10% saturated, 13% monounsaturated, and 77% polyunsaturated fatty acids.

The more saturated fatty acids in an oil the more likely it will be solid at room temperature. The more unsaturated fatty acids, the more liquid it will be.

It's also not correct to say that saturated fats are bad and unsaturated fats are good. It's not that simple. The length of the fatty acid also makes a difference. So, let's talk about that next.

Fatty Acid Length

To the right is a graphic showing the length of various saturated fatty acids. Fatty acids are categorized as short, medium, and long-chained. The short-chain fatty acids have less than six carbon pairs. The longer chained ones have eleven or more. In between are the medium-chained fatty acids.

Oils high in medium-chained fatty acids, known as medium chain triglycerides or MCTs for short have been discovered to have many health benefits. So have short-chained fatty acids. This is why it's overly simplistic to categorize all saturated fats as bad. Coconut oil, palm oil, butter, and even lard have a lot of medium and short-chained saturated fatty acids and can be healthy.

The real source of bad fats is the modern refined vegetable oils and deep-fried foods. So, let's talk about those.

Unsaturated Oils and Transfats

There's a problem with unsaturated fats. The double bonds are sites on the molecule where the fat can be oxidized. In other words, a molecule of oxygen can attach where the double bond is located in place of two hydrogen atoms. Remember that oxygen has two hands. This makes the oil rancid, which not only gives it an off taste, it also ruins the oil nutritionally. There is evidence that it is oxidized or rancid fats that stick to your arteries and contribute to cardiovascular disease.

There is also a problem when these oils are heated. Polyunsaturated fats form something called trans fats when used for cooking. The higher the heat and the longer they are used, the more trans fats they will form.

To understand trans fats, we need to look again at fatty acid structure. Normally, in an unsaturated fatty acid, the hydrogen molecules in a double bond are attached on the same side. This is known as a cis-fatty acid. It's cis-fatty acids that bend as shown in the illustration on the left. In a transfat, the hydrogen molecules attach to opposite sides of the double bond. This keeps the fatty acid straight so it acts more like a saturated fat than an unsaturated fat.

There's a lot of research suggesting transfats are unhealthy. First, like oxidized fats, they are also associated with arteriosclerosis and an increased risk of heart disease. They also increase insulin resistance and contribute to diabetes, something they have in common with long-chain saturated fats. They may also increase inflammation and cancer risk. The biggest source of these transfats is processed foods and foods that have been deep-fried in vegetable oils that have been repeatedly reheated.

Refining and Hydrogenating Oils

To increase shelf life, vegetable oils are refined and may also be partially or completely hydrogenated. Let's look at both of these processes.

Fresh oils pressed from nuts and seeds contain vitamins, minerals, and other nutrients. Because these other nutrients decrease shelf life, they are removed from oils, just like nutrients are removed from sugar and white flour. Plus, the extraction process itself can involve heat which causes transfats to form.

Processed oils are de-gummed to remove phospholipids like lecithin and minerals like iron, copper, calcium, and magnesium. Sodium hydroxide may added to remove free fatty acids (fatty acids which are not attached to glycerine molecules). This removes more minerals and phospholipids. Oils are then bleached and deodorized to remove beta-carotene, aromatic oils, (which give natural oils flavor and odor), and any remaining free fatty acids.

Fat-soluble vitamins, which are present in many natural fats may also be removed. Vitamins like vitamin A (both carotenoid and retinol forms), vitamin D, and vitamin E help prevent oils from oxidizing. The lack of these vitamins also contributes to heart disease and other chronic health problems.

Hydrogenation is a process that is used to add hydrogen molecules to some of those carbon bonds. Most commercial cooking oils, and all margarine and shortening products, are composed of partially hydrogenated fats. To say that another way, some of their unsaturated fatty acids have been turned into saturated fats. The problem is that in nature these hydrogen molecules are added in a controlled way, while in the hydrogenation process, they are added randomly. This results in the production of trans fats.

Choosing Healthy Fats

The best sources of fat are natural foods eaten in their whole-food form. These fats contain the vitamins, minerals, and other nutrients destroyed in the refining process. Good plant sources of fat include avocados, nuts (particularly walnuts, macadamia nuts, and almonds), and seeds (e.g. hemp, flax, and chia). These foods can provide a feeling of fullness that helps you eat less, as well as the fatty acids you need for good health.

Contrary to popular belief, not all animal fats are bad. The biggest problem with animal fat is its source. The fatty acid profile in animals raised in feed lots is very different from that of animals raised on pasture or obtained from wild sources. Also, many toxins accumulate in fat, so animals that are fed food containing pesticides or are given chemicals to fatten them up or increase production of milk and eggs, will have less healthy fats.

On the other hand, if you can get organic, grass-fed animal products like eggs, butter, cream, whole milk, raw cheese, poultry, or even red meat, enjoy them. Fish can also be a good source of healthy fats, including wild-caught salmon, sardines, tuna, wild-caught trout, and herring.