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The Absolutely Worst & Best Fats for the Keto Diet

The Absolutely Worst & Best Fats for the Keto Diet

The ketogenic lifestyle contradicts the prevailing belief that “fat is bad.” In fact, the Keto Diet is based on the exact opposite idea. On the Keto Diet, fat should be the biggest source of calories (about 60-80% depending on your individual macronutrient needs). But not all fats are created equal. This is why it’s so important to know your fats. So… which are the best fats to eat, and which fats should you avoid?

Unfortunately, learning about all the different types of fats can get a bit confusing. You’ve probably heard of saturated and unsaturated fats as well as trans fats. But then there are omega fatty acids (3, 6, 9 and others), short-chain and very-long-chain fats (and everything between), MUFAs and PUFAs, and the list goes on and on. You get the picture.

Luckily, the science is actually quite clear. Fats are not all “bad.” Far from it. They are crucial to a well-functioning body and brain. The body burns fats as fuel for energy. Fats provide the building blocks for many crucial substances in our bodies (such as hormones) as well as new cell membranes.

No matter what the USDA claims, low-fat diets are not the answer. What is important, however, is to consume foods that provide an appropriate balance of fatty acids. So let’s sort through all the fun fat facts to figure out the best fats you should eat while on the Keto Diet, and why.

Different Fat Classifications

One reason it can be difficult to understand all the different types of fats is that there are several different ways of classifying them. Fats are made up of fatty acid chains of various lengths with specific properties. Chemically, they are hydrocarbon chains that either have:

  • single bonds between the carbon and hydrogen atoms (making them saturated)
  • one double bond because they are missing a pair of hydrogens (making them monounsaturated)
  • more than one double bond because they are missing more than one pair of hydrogens (making them polyunsaturated)

They also have an “acid group” at one end and an “omega end” at the opposite end. (Try to remember this because there will be a pop quiz at the end. Just kidding. But we will come back to this in more depth later.)

It’s this varying hydrogen saturation that is the most common basis for classifying fats. But they can also be classified by the length of their molecules (aka “chain length”). And it’s smart to pay attention to the type of omega end (3, 6, 9 etc) they have, too.

Saturated Fats

Saturated fats are straight chains of carbon that are completely loaded with tightly stacked hydrogen atoms. They are saturated because they cannot hold any more hydrogen atoms than they already do. You can recognize them in your kitchen because they are typically solid at room temperature and quite stable in your pantry or fridge. Saturated fats are abundant in lots of animal products, but they are also found in coconuts—the darling of plant-based saturated fats.

Unfortunately, saturated fats have been getting a bad rap for several decades! The USDA, other official government agencies, and many medical associations blame saturated fats for the rise in cardiovascular disease and obesity. But it’s not that simple!

The human body is actually made up of lots of saturated fat (and monounsaturated fats), so it requires quite a bit of them to function properly. Many saturated fats are actually among the best fats you can eat, especially if you pay particular attention to your sources. (The reason the source is important is because this affects the omega end. More on this later).

Health Benefits of Saturated Fats

The statement that saturated fats are some of the best fats for you might seem really controversial. But let’s look at the science. Tim Ferris (we are huge fans!) has a very informative post on the reasons to eat more saturated fats, backed by research done by Dr. Michael Eades and Dr. Mary Dan Eades, two bariatric (obesity treatment) doctors in the US. Let’s summarize the evidence. Saturated fats can improve your healthy by:

  • Lowering the risk of cardiovascular disease
  • Strengthening your bones and promoting normal bone density
  • Protecting your liver from alcohol and medications
  • Providing your lungs with a necessary layer of lung surfactant (which is made of 100% saturated fatty acids)
  • Fueling your brain with optimal nutrition
  • Helping your nerves send proper signals (especially those that influence metabolism)
  • strengthening your immune system by keeping your white blood cells “on alert” for foreign invaders

Now that is quite the list! (Pass the bacon, please!)

Unsaturated Fats

Unsaturated fats have hydrocarbon chains with at least one missing pair of hydrogen atoms. They could hold more hydrogen, which is why they are called unsaturated. The missing hydrogen gives the fatty acid chain a “kink” or a bend. The more hydrogen pairs that are missing, the more bent the chain appears. And the more bent the chain is, the more space if occupies. This is why unsaturated fats appear as liquid oils at room temperature.

Most of us have probably heard that unsaturated fats are the best fats to eat. There is no shortage of advice out there about replacing “bad” saturated animal fats with “good” unsaturated plant oils. While it’s true that many unsaturated fats are some of the best fats you can eat, this doesn’t mean that all unsaturated fats are good.

Once again, it is not that simple! Let’s take a deeper look at the worst and the best fats in this group.


There are two types of unsaturated fats: monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs). And they are not created equal. Chemically speaking, MUFAs are missing just one pair of hydrogens while PUFAs are missing two or more.

The more pairs that are missing, however, the more unstable the fat molecule becomes. This is very important because unstable fats are more likely to go rancid, releasing oxygen free radicals that may damage your cells. Stability is the most important factor in MUFAs’ and PUFAs’ effects on your health. Rancid PUFAs can be much more harmful than the “dangerous” saturated animal fats that the USDA warns us about.

MUFAs on the other hand are only missing one pair of hydrogens, so they are fairly stable. Monounsaturated fats help protect against metabolic disease and can assist in maintaining healthy cholesterol levels. A diet high in MUFAs may help to reduce the risk of type-2 diabetes, atherosclerosis, high blood pressure, coronary heart disease and stroke.

PUFAs, however, are quite unstable oils, which makes them susceptible to oxidative rancidity. They are found in many processed vegetable oils, such as corn oil and soybean oil. Vegetable oils that sit around in your pantry for a long time are especially prone to going rancid because of the instability of their fat chains. So toss them out!

Not all PUFAs are dangerous though. Eating perishable foods that naturally contain PUFAs, such as oily fish, flaxseeds, and walnuts, is perfectly fine. The key here is that these foods are highly perishable and need to be kept refrigerated (or frozen) and consumed promptly. This is is why it is recommended to only buy whole flaxseeds and store them in the fridge. If you can, store your nuts in the fridge or freezer, too, to avoid them going rancid too quickly. Don’t let these valuable foods sit around and go rancid!

Avoid Trans Fats

The unstable nature of PUFAs is why the industrial food processing industry developed the process of hydrogenation. This is a way to force unstable vegetable oils to become saturated with hydrogen, which hardens them and prolongs their shelf life. (Except who wants to eat food that’s been on a shelf for 6 months or more?) You’ve probably seen “partially hydrogenated oils” (PHOs) listed on lots of ingredient labels on processed foods. The reason they are so popular in the food processing industry is because they don’t “go bad,” which is ironic since they are already very, very bad.

Unfortunately, the industrial process of hydrogenation (and partial hydrogenation) is very dangerous because it forms trans fatty acids, which are now recognized as very unhealthy. Even the FDA states that removing PHOs from processed foods could prevent thousands of heart attacks and deaths each year. The FDA also determined that trans fats are not “generally recognized as safe” (GRAS). In fact, we shouldn’t even be consuming any added trans fats at all!

These dangerous trans fats are found in margarine, fried foods, snack foods, processed baked goods, and ready-to-bake dough products. Some trans fats do also occur naturally in dairy and meat, but the amounts are so small that they do not pose any health risks. It’s the man-made, artificial trans fats that are the real killer!

Classification by Chain Length

Fatty acids also differ from each other by the length of their carbon chains. A typical fatty acid chain contains 12–24 carbons, but some may have as few as 2 carbons or as many as 80. With all the talk about dietary fat contributing to unhealthy cholesterol levels, it’s eye opening to know that there are only a few chain lengths that actually impact cholesterol. Those are the C:12, C:14 and C:16 saturated fatty acid chains. (The rest of your cholesterol is actually produced by your own liver as a way to help protect the body from inflammation.)

While you can’t always tell which fats have short chains and which fats have long ones, there are some clues to help you. As a rule of thumb, the higher the melting point of a particular fat, the longer its chain of hydrocarbons. Basically, fats that are solid at room temperature typically have longer chain lengths than fats that are liquid (oils) at room temperature. If you drew the conclusion that saturated fats have longer chains and higher melting points than unsaturated fats, you are correct! Even when the chains are of equal length, saturated fats melt at a higher temperature than unsaturated fats.

There are four different groups in this classification schema, roughly classed as follows:

  • Short chain fatty acids (SCFA) can have up to 6 carbon atoms
  • Medium chain fatty acids (MCFA) have from 8 to 12 carbon atoms
  • Long chain fatty acids (LCFA) have from 14 to 18 carbon atoms
  • Very long chain fatty acids (VLCFA) have more than 24 carbon atoms

So which are the best fats based on chain length?

Again, this is not a simple answer. Unfortunately, the Standard American Diet (SAD) is very unbalanced. The typical American gets more than enough LCFAs from pork, beef, eggs, and vegetable oils, such as sunflower and safflower oil.

By contrast, most people do not consume nearly enough MCFAs. MCFAs are used as energy by the body and are easy to break down. They have been shown to reduce body fat and hunger. MCFAs are found in palm kernel oil, coconuts and coconut oil, and of course as MCT oil. The Keto Diet emphasizes coconut oil and MCT oil not only in order to keep hunger under control, but also to bring the ratio of LCFAs and MCFAs into greater balance. Another reason MCFAs are one of the best fats you can eat!

Finally, SCFAs are mainly produced by the body. Or should I say “in the body?” It is actually our own beneficial gut bacteria that produce most of the SCFAs we need. They are produced in the large intestine during the fermentation of soluble dietary fiber. Luckily, since the Keto Diet limits soluble fiber (it’s considered a carb), butter is a good source of SCFAs.

The Omega Family

Last, but not least, you often hear about “omegas” and essential fatty acids. What’s the scoop on that? How do you know how to choose the best fats in this category? Let’s take a look.

Remember that whole bit we talked about in the beginning about unsaturated fats having missing pairs of hydrogen? Remember how the number of double bonds determines how fluid and bendy the fatty acid chain is, and whether it acts as a solid or liquid at room temperature?

Well, the story doesn’t end there. The end with the missing hydrogens and the double bonds is the “omega end.” The third classification of fatty acids is based on the omega end. If the first double bond involves the third carbon atom, the unsaturated fat is classified as an omega-3. When the first double bond involves the sixth carbon atom, the fatty acid is classified as an omega-6. And when the first double bond involves the ninth carbon atom, it is classified as an omega-9. You get the picture.

Both MUFAs and PUFAs contain omegas, but omega-3s and omega-6s are always PUFAs. While both are PUFA omegas, the position of the first double bond impacts how the body metabolizes the fatty acid, and how it is used by cells. This is why omega-3s and omega-6s affect the body in very different ways.

You’ve probably heard that omega-3s are good for you, have anti-inflammatory and blood-thinning actions, and support brain development and learning. And that most omega-6s, by contrast, can cause inflammation, increase blood stickiness, and contribute to heart disease. (The exception to this is gammalinolenic acid. GLA is in evening primrose, blackcurrant and starflower oils. This fatty acid can actually help reduce inflammation if eaten in sufficiently high quantities.)

In an ideally balanced diet, the ratio of omega-3s to omega-6s would be 1:1 or 1:2, but the SAD has a ratio that is more like 1:10 or even 1:20! This means that most Americans eat way too many unstable omega-6 PUFAs. And that contributes to a host of health issues.

Essential Fatty Acids

Our bodies have the ability to make MUFAs as well as most PUFAs from other fats in our diet. They cannot, however, make any omega-3s or omega-6s. For this reason, these two omegas are called “essential” even though they are not actually “essential” to our health in nearly the same ways.

Let’s go back one moment to trans fats and PUFAs. Remember how trans fats are artificially hardened by hydrogenation? Remember how PUFAs are unstable due to all those missing pairs of hydrogens?

Well, if your diet doesn’t contain enough beneficial fatty acids, your body has to use whatever other fatty acids happen to be available. This might mean that your body ends up using those unstable PUFAs or even harmful trans fats to build new cell membranes. It’s not surprising that your health suffers when these subpar fatty acids are incorporated into your cell membranes. They build weak, inflexible cell membranes that easily suffer oxidative damage. Many modern research studies show that this overabundance of harmful fatty acids in the body is the real reason for coronary disease. Atherosclerotic plaque, for example, is caused by the oxidation of PUFAs in your LDL membrane—not by eating too much dietary cholesterol!

Sourcing the Best Fats

Now that you know pretty much all the basics about fats, there is just one last piece of information to consider before we can really decide on the best fats for the Keto Diet. The things is, all dietary fats are made up of a blend of all the different kinds of fats we discussed in this article.

As a general rule of thumb, animal-based foods contain a higher percentage of saturated fat than vegetable foods. But then we have coconut, which is the highest in saturated fats of all fats. We also know that butter, lard and bacon, which are traditionally viewed as “a heart attack waiting to happen,” also contain significant amounts of the “healthier” unsaturated fats. And coconut, which does not contain many unsaturated fatty acids at all, is considered healthy because it is made up of MCFAs, which most of us do not eat enough of.

We also learned that all those so-called “healthy” unsaturated fats are actually not at all created equal. Many PUFAs are unstable and potentially dangerous. But then some PUFAs are essential to good health thanks to their omega-3 content. Is your head spinning yet?

And to complicate it further, the quality of the fats we eat, and specifically the ratio of omega-3s to omega-6s in them, can vary quite a bit depending on how they were produced, the diet or nourishment they received, and their genetic make-up. This is why it’s so important to consider the source of both saturated and unsaturated fats you consume. The best fats come from (surprise, surprise!) nature, and haven’t undergone much, if any, processing.

Bottom Line on the Best Fats to Eat on the Keto Diet

On the Keto Diet, some of the best fats you can eat are saturated fats. Try to purchase organic, grass fed, pastured or wild sources of fat whenever possible. Feel free to enjoy:

  • fatty cuts of meat (hello bacon!)
  • cheese
  • whipping cream
  • butter and ghee
  • tallow
  • lard
  • drippings
  • eggs
  • coconut oil
  • MCT oil

In the unsaturated fat category, look for hand pressed, cold pressed or expeller (screw) pressed oils never heated above 122°F. Ideally, chose oils packaged in dark amber bottles to protect from air and sunlight, which cause oxidation. You may also want to consider how long you plan to store foods that contain unsaturated fats, and make an effort to store them in the fridge or freezer. And don’t forget to eat these foods in a timely manner.

  • olives and olive oil
  • oily fish (mackerel, herring, salmon, trout, sardines, fresh tuna)
  • avocado and avocado oil
  • nuts (especially macadamia and walnut)
  • seeds
  • expeller pressed oils from nuts and seeds
  • peanuts
  • nut butters

To ensure you’re getting enough foods rich in omega-3 essential fatty acids, choose:

  • oily fish (mackerel, herring, salmon, trout, sardines, fresh tuna)
  • wild game (venison and buffalo)
  • grass-fed beef
  • omega-3 enriched eggs
  • omega-3 fish oil supplements

Reduce or eliminate all foods containing inflammatory omega-6s, such as:

  • industrial vegetable oils (safflower, grapeseed, sunflower, corn, cottonseed and soybean oil)
  • stick margarines and spreads (sunflower or safflower oil)
  • convenience foods
  • fast food, and store-bought snacks
  • processed foods (doughnuts, cakes, pie crusts, biscuits, frozen pizza, cookies, crackers, chips etc)

Also strictly avoid:

  • hydrogenated/partially hydrogenated oils

(Note: It is not enough to just look at the nutrition label. Food processors do not have to list trans fats on the nutrition label if each serving contains under 1 gram. Be sure to read the ingredient list and avoid all products with PHOs.)

Want to learn more about what to eat on the Keto Diet? Check out 5 Ways to meal Prep for the Keto Diet.

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