Understanding Fats

With all the food advertisements you encounter on TV daily and the numerous nutrition updates you hear on the news, you're bombarded with tons of information about the fats in your diet. You’ve likely come across the following terms:

Ever wondered what all these terms mean or why they matter? Why not just indulge without a care? In this article, you’ll learn what these terms signify and how different fats in food impact your body. But first, let’s break things down into practical terms.

You can find pure fats in three sections at the grocery store:

The rest of the store is, of course, filled with fats and oils, though they're less apparent. Potato chips and french fries are fried in oil, cookies and cakes contain fats and oils, and much more. This is how we get the fats we need each day. And we do need fat — as you'll learn, there are essential fats our bodies require to function properly.

So, what exactly are these fats and oils made of? To truly understand fat, you’ll need to dive into a bit of chemistry. To discuss fat, we need to begin with fatty acids.

What is a Fatty Acid?

A fatty acid consists of a long chain of hydrocarbons, ending with a carboxyl group (COOH). Several well-known fatty acids exist, and four of them are shown below, along with acetic acid for comparison purposes:

The COOH group is what makes these molecules acidic. You’re likely familiar with acetic acid, the main acid in vinegar. Fatty acids are similar to acetic acid, but they feature much longer carbon chains.

To form a typical fat, three fatty acids bond with glycerol to create a triglyceride, as shown below:

This specific triglyceride contains three molecules of stearic acid, which gives it the name tristearin. The diagram depicts a fat molecule. When you consume fat, you're ingesting clusters of molecules like these. The types of fatty acids in the fat determine many characteristics, including whether the fat is solid or liquid at room temperature, its appearance, and its health impact. These factors are influenced by whether the fat is "saturated" or "unsaturated."

Saturated vs. Unsaturated

Looking at the chains of palmitic acid and stearic acid, you’ll notice that their carbon chains are fully and evenly filled with hydrogen atoms.

In other words, these chains are saturated with hydrogen. Fats (triglycerides) containing palmitic and stearic acids are referred to as saturated fats. These fats are solid at room temperature. On the other hand, oleic acid is not saturated. Two carbon atoms are connected by a double bond, and two hydrogen atoms are missing. This makes oleic acid unsaturated. Fats with a high amount of oleic acid remain liquid at room temperature, which is why they are classified as oils.

Oleic acid, possessing a single double bond, is classified as mono-unsaturated. Fatty acids containing multiple double bonds, such as linoleic acid shown in the first figure, are termed polyunsaturated. Polyunsaturated fats also remain liquid at room temperature.

For example, if you have corn oil, it’s a polyunsaturated oil with a high concentration of linoleic acid. Since it’s polyunsaturated, it stays liquid at room temperature. To turn it into margarine, you’d hydrogenate it—adding hydrogen atoms to saturate the oil. This is done by heating the oil, introducing pressurized hydrogen gas, and using a nickel catalyst. The result is "partially hydrogenated vegetable oil," commonly found in vegetable shortening and margarine.

Fat and Health

Current nutrition science highlights mono-unsaturated fats as the healthy fats. Olive oil and canola oil are both examples of these fats. Mono-unsaturated fats are believed to help reduce cholesterol levels.

The fats to avoid are generally the saturated ones. These fats are harmful because they block your arteries. Partially hydrogenated vegetable oils, which are chemically altered saturated fats, are now considered harmful, not just because of their saturation, but due to a byproduct of hydrogenation called trans fatty acids.

Fatty acids with double bonds exist in two types: trans and cis. The terms "trans" and "cis" describe the way the carbon bonds fold in unsaturated fatty acids. Cis fatty acids have the natural, regular fold direction, while trans fatty acids, although chemically identical to cis, fold unnaturally. Trans fats are formed through heating (like deep frying) or hydrogenation.

In the body, enzymes responsible for fat processing struggle to handle trans fatty acids (refer to How Cells Work for more on enzymes). As a result, these enzymes become occupied with trans fats, which can disrupt the processing of essential fatty acids.

Essential fatty acids, unlike trans fatty acids, are crucial for good health. They are not harmful and are actually vital for maintaining overall well-being.

Essential Fatty Acids

The most prevalent fatty acids are found in animal fats, and they include the following:

Your body can create these fatty acids whenever there is a caloric surplus. If you consume enough sugar, your body can convert that sugar into fats (see 'How Food Works' for a deeper dive into carbohydrates and sugar).

There is another category of fatty acids known as essential fatty acids, which your body cannot produce. These fatty acids include:

Since your body cannot produce these essential fatty acids, you must obtain them through your diet.

Essential fatty acids are divided into two main groups: omega-3 and omega-6. The numbers 3 and 6 refer to the position of the first carbon double bond in the fatty acid chain. All essential fatty acids are polyunsaturated, so the numbers 3 or 6 indicate the position of the first double bond, either three or six carbons from the end of the chain.

Omega-6 fatty acids are found abundantly in oils like corn, sunflower, and soybean oils. Omega-3 fatty acids, on the other hand, are rarer and can be found in flax seeds, pumpkin seeds, walnuts, and fish such as salmon, trout, and tuna. Current dietary recommendations suggest that the balance of these two types of fats should be closer to a 1-to-1 or 2-to-1 ratio, rather than the typical 20-to-1 ratio seen in most Western diets. To achieve this balance, you might need to supplement your diet with omega-3 oils or eat fish regularly, ideally two or three times a week.

To sum up, here's the current scientific perspective on fat consumption: