FAT. Ooh, it feels like such a naughty word, doesn’t it?

It’s as if just saying it aloud will automatically add inches to our waistlines. And animal fats like butter or lard? Instant cardiac arrest.

At least this is what we’ve been wrongly led to believe for decades.

It’s time we set the record straight when it comes to fat.

I’ve already been over the details of why fat is a necessary part of a healthy diet, but here’s a quick reminder:

• Fat provides a concentrated source of energy in the diet, keeping you feeling fuller for longer. Contrary to popular belief, this can actually help you lose weight.
• Fat is a key component of cell membranes, and properly functioning cell membranes are vital for a properly functioning body.
• Fat is a necessary co-factor in the creation of prostaglandins, hormone-like substances that are critical to the body’s healing process.
• Fat plays a vital role in hormone regulation.
• Fat is needed for the absorption of the fat-soluble vitamins A, D, E, and K.
• Fat is necessary for healthy liver and gallbladder function.

So what is fat, exactly?

First things first, fat is a nutrient. Just thinking of fat in this way helps us to view it in a different light — as a necessary part of a healthy diet — since we tend to associate “nutrients” positively with health.

Chemically-speaking, fat is a collection of molecules called triglycerides, which are formed from 3 fatty acids attached to a glycerol molecule. Fatty acids are chains of carbon atoms with hydrogen atoms filling the available bonds. Different fatty acids have different molecular arrangements, which causes them to act very differently.

There are 3 primary categories of fatty acids, and each plays an important role in the body.

It should be noted that most of the foods we eat — from eggs to apples — contain a mixture of these fatty acids, not strictly one or another.

Saturated fat

In the molecular structure of saturated fatty acids, all carbons are saturated with hydrogen and there are no unfilled bonds. For this reason, saturated fats are highly stable — they are ideal for high-heat cooking, they do not go rancid easily, and they are solid or semi-solid at room temperature.

OK let’s address the elephant in the room… saturated fat has a bad reputation! It has been wrongly accused of causing heart disease since the mid-1900s. In fact, the line between the demonization of saturated fat and the demonization of fat as a whole is pretty blurry. But the story (really, the “lipid hypothesis”) goes a little like this: dietary cholesterol was wrongly believed to cause heart disease, dietary cholesterol is found in animal sources of saturated fat, therefore saturated fat should be avoided. But this story was largely based on grossly misinterpreted studies and did not take other factors into consideration (like the increased intake of processed carbohydrates, refined and hydrogenated plant oils, or sugar). Study upon study has debunked the connection between saturated fat and heart disease, yet the story continues to stick. Luckily, mainstream media (get a load of this TIME cover story from June 2014) is finally starting to see this story for what it really is: a fable.

Now let’s look at the important roles saturated fat plays in the body. It is necessary for proper cell structure (saturated fatty acids constitute at least 50% of cell membranes) and therefore proper cell function. It is also a major player in bone health as it is a necessary cofactor for calcium to be effectively incorporated into the skeletal structure. Saturated fat also protects the liver from alcohol and other toxins, and enhances the immune system. Furthermore, saturated fats are easy for the body to digest, making them ideal for those with gallbladder or GI issues.

★ So is saturated fat healthy?

Contrary to popular belief YES! Healthy sources of saturated fat include grass-fed meat and raw/organic dairy products; whole coconut; coconut butter/manna; and unrefined, cold-pressed coconut and red palm oil. These oils are great for high-heat cooking and baking because of their stability.

Monounsaturated fat

In the molecular structure of monounsaturated fatty acids, there is 1 available hydrogen bond that hasn’t been filled. As a result, monounsaturated fats are relatively stable — they are not ideal for high-heat cooking but may be used for low-temperature cooking, they do not go rancid very easily, and they are liquid at room temperature.

Monounsaturated fat is the simple one of the group — it is pretty much unanimously accepted as healthy across the board. If you do research on the World Wide Web, most sites still regurgitating the old “Artery-Clogging-Saturated-Fat” fable will say it’s because you can use these oils to healthfully replace saturated fat in your diet. Really, these fats should be consumed along with the healthy sources of saturated fats we’ve already discussed.

★ So is monounsaturated fat healthy?

YES! Healthy sources of monounsaturated fat include avocados, olives, almonds, hazelnuts, and macadamias, as well as their oils. However, be sure to always choose cold-pressed and/or extra virgin sources of monounsaturated oils, and choose products in dark glass bottles which will help protect these more fragile fatty acids. They are fine for low-heat cooking, but should not be used for frying or high-heat cooking.

Polyunsaturated fat

In the molecular structure of polyunsaturated fatty acids, there is more than 1 unfilled hydrogen bond. For this reason, polyunsaturated fats are unstable — they are not ideal for any cooking/ or heating, they go rancid easily (need to be refrigerated and stored in dark containers), and are usually liquid at room temperature. This is why you must be very careful with these fats.

Polyunsaturated fatty acids can be subdivided into omega-3 (alpha-linolenic acid) and omega-6 (linoleic acid) fatty acids. These are known as the Essential Fatty Acids (EFAs) since our bodies can’t produce them and they must be obtained from our diet. However, we really don’t need many of them for optimal health — they should constitute just 4% of our daily caloric intake. Omega-3 fatty acids are very anti-inflammatory, support brain function, and have even been shown to reduce symptoms associated with ADHD and depression. Omega-6 fats also brain function, support the immune system, and help with overall growth and development.

That being said, an excess of omega-6s in our diets is unhealthy — when omega-6 consumption greatly exceeds omega-3 consumption, the body becomes overloaded with inflammatory arachidonic acid. Ideally, the ratio of omega-3s to omega-6s in our diet would be 1:1. But because of the widespread use of cheap “vegetable” oils in processed foods (ugh), and the widespread consumption of processed foods (double ugh), most Americans’ consume these essential fatty acids in a 1:10 to 1:20 ratio. That is, they’re consuming far too many omega-6s.

★ So is polyunsaturated fat healthy?

YES! and NO. As previously mentioned, 1) we must be very careful with these unstable fats, and 2) we generally get a lot more omega-6s than omega-3s in our diets, and we need to work to change this. For this reason, omega-3 polyunsaturated fatty acids should be sought out while omega-6 polyunsaturated fatty acids should generally be avoided (you will get a sufficient amount from other sources). Healthy sources of omega-3 polyunsaturated fatty acids include wild-caught fish, grass-fed meat, and eggs, as well as walnuts, wheat germ, flax seeds, hemp seeds, and pumpkin seeds. Be sure to keep them refrigerated and stored in dark containers. The cheap crop oils — canola, sunflower, safflower, soybean, grapeseed, corn, and cottonseed — contain the most omega-6s, and are virtually devoid of omega-3s. Therefore, it is best to avoid these oils. These oils should also NEVER be used for cooking, and it is best to avoid processed foods (even organic) containing these oils.

The fake fat to avoid like the plague: trans fat.

Trans fats are a byproduct of hydrogenation, the process that solidifies any oil that would otherwise be liquid at room temperature — namely vegetable oils (canola, corn, cottonseed, etc.) — by forcing hydrogen atoms into the oil’s structure using a chemical catalyst. Once upon a time, they were called “plastic oils” by food chemists (yum).

As previously mentioned, many cheap polyunsaturated omega-6 oils (“vegetable”, canola, corn, cottonseed) are very fragile and can easy spoil. But hydrogenation makes these oils less vulnerable to damage, thus increasing their shelf-life, or the shelf-life of any processed food containing these oils.

So why is this so dangerous?

When one hydrogen atom is moved to the other side of the fatty acid molecule during hydrogenation, the ability of living cells to make reactions at the site is compromised or altogether lost… [Trans fats’] altered chemical structure creates havoc with thousands of necessary chemical reactions — everything from energy provision to prostaglandin production.

Trans fats cause chronic inflammation, which can increase the risk of cardiovascular disease and Type 2 diabetes, and lead to insulin resistance, according to the Harvard School of Public Health. Harvard also reports that for every 2% increase in daily calories from trans fat, the risk of coronary heart disease increases by 23% (wow wow wow wowza!!).

Sources and Further Reading:

• 6 Graphs That Show Why The “War” on Fat Was a Huge Mistake, Authority Nutrition
• The Questionable Link Between Saturated Fat and Heart Disease, The Wall Street Journal
• Know Your Fats, Dr. Mary Enig
• Nourishing Traditions, Sally Fallon
• Eat The Yolks, Liz Wolfe
• Put Your Heart In Your Mouth, Dr. Natasha Campbell-McBride
• 9 Steps to Perfect Health – #2: Nourish Your Body, Chris Kresser