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Good Fats VS Bad Fats

Last updated: May 10, 2020 at 7:44PM | - Published on: Nov 27, 2018

Written by Sarah Neidler, PhD

Scientifically Reviewed by Raphael Sirtoli, MSc

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The different kinds of fats

Fats make up most calories on a ketogenic diet, anywhere from 60 to 85% of calories. So make sure you know which ones are healthy and which ones you should diligently avoid.

Why is this so important? Because bad fats, such as seed oils and industrial trans fats carry many substantial health risks [1,2,3,4].

There are two different kinds of fatty acids: saturated and unsaturated. Unsaturated fatty acids are further divided into monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs). Mono- means ‘1’ and poly- means ‘many’.

So polyunsaturated fats are have more unsaturated bonds than monounsaturated fats. Don’t worry, you don’t need to know what those kinds of bonds really mean right now. Fats are stored in the body as triglycerides, which are comprised of a glycerol molecule connected to three fatty acids.

Saturated fatty acids

Science Corner

A fatty acid is a long chain of carbon atoms connected by one carbon-carbon bond (C-C) with a carboxyl group on its end. By ‘saturated’ we mean that it’s filled to capacity (with hydrogen atoms).

Different saturated fatty acids can be distinguished by how long the chain is (i.e., how many carbon atoms make up that chain which is how much energy they carry). A relatively short one such as caprylic acid (used in MCT oil) contains 8 carbon atoms. Very long fatty acids include 22 or more carbons, like cerotic acid found in beeswax which has a whopping 26 carbons!

Saturated fatty acids are not essential in the dietary sense, meaning that our body is able to make its own and thus we don’t need to seek them out in our diet. However, they are a great source of energy and naturally present in foods that do contain essential fats (and amino acids which make up protein) so it’s actually not possible to avoid them – and you shouldn’t anyways! They’re especially useful as a main source of energy on a ketogenic diet.

The big advantage of saturated fatty acids is that they are very stable, meaning they don’t go rancid when left out on the counter. In other words, when heated they stay in the ‘shape’ your body is used to handle. They’re great for cooking since they can be heated to very high temperatures (e.g. frying). For example, coconut oil is a saturated fatty acid that doesn’t need to be stored in the fridge. This is in contrast to unsaturated fatty acids, which we will talk about later.

In the past, saturated fatty acids were thought to cause heart disease. Nowadays we know that this is not true [5,6,7]

But because this idea has been ingrained in our brains for ages, changing the stigma around it is very difficult. It also doesn’t help that certain organizations like the American Heart Association still recommend keeping calories from saturated fat between 5 to 6% [8]. This is an example of how long it can take for public authorities to reverse incorrect scientific stances, let alone admit fault.

Picture of an healthy artery vs clogged artery because of dietary causes like seed oils, flour, sugar. Animal fats or saturated fats don't cause heart disease. Injury to the endothelium, chronic inflammation and excessive oxidative stress can cause heart disease.

One of the most popular kinds of saturated fat in the ketogenic diet are medium chain triglycerides (MCTs), which are 6 to 12 carbons long. Why are they so popular? This is because MCTs are metabolized quickly in the liver to form ketones and are preferentially used as energy before other kinds of fats.

Coconut oil is technically 65% MCT oil. However, most of its MCTs are monolaurin (12 carbons long) which is less ketogenic than the MCTs called caprylic acid (8 carbons long) or capric acid (10 carbons long). Mixes of these C8 and C10 MCTs can be purchased in MCT oil products [9].

Unsaturated fatty acids

Science Corner

Unsaturated fatty acids are different than saturated ones because their chains aren’t linked by saturated carbon bonds but by double (unsaturated) ones. This gives them more ‘fluidity’ than the ‘rigid’ saturated fats made with single bonds.

It’s more complicated, but the mix of saturated and unsaturated bonds as well as the length of the fat chains gives different fats their different properties.

For example, these double-bonds can be in a cis (parallel) or trans (like a crossroads) which will affect things like melting point and can have specific impacts on our health – both good and bad.

Mainstream nutrition sees unsaturated fats as the good guys – but that’s too simplistic or even wrong. Even advocates of very low-fat diets admit that unsaturated fats are beneficial for health, especially the famous oleic acid found in olive oil. Although true that plant fats are generally unsaturated, that’s overly simplistic too. Both animal and plant food sources contain a mix of saturated, monounsaturated and polyunsaturated fats.

Did You Know?

Bacon is villainized and misunderstood. If I’m trying to get lots of monounsaturated fat (for whatever reason), am I better off eating 100g of olives or bacon? Most people would answer olives – duh.

Wrong! 100g of bacon contains about 45g of fat of which 20g are monounsaturated and 15g saturated, whilst 100g of olives contains a bit more than 15g of fat of which around 11g are monounsaturated and 2g saturated [9,10].

This means that, per weight, bacon has nearly twice as much more monounsaturated fat than olives do. However, this is not why bacon is a healthy food. But it’s something most get wrong about bacon.

The effects of unsaturated fatty acids on human health are as diverse as is their complex chemistry. While the pendulum of scientific opinion swings both ways on unsaturated fatty acids being good or bad, polyunsaturated fats can have a positive health impact in the right amounts, from the right sources and are indeed essential. ‘Essential’ here means that we cannot make them ourselves and therefore must be obtained from external sources.

However, concentrated sources of polyunsaturated fats (PUFAs) are very unhealthy (e.g. sunflower oil). This is because we didn’t evolve to handle them in such high amounts. Additionally, their double bonds make them unstable, more prone to rancidity, oxidation, or hydrogenation, especially when subjected to harsh chemical processing.

Monounsaturated fatty acids

Science Corner

MUFAs have 1 ‘fluid’ double bond (C=C) and the rest of its chain is made ‘saturated’, ‘rigid’ single bonds (C-C).

Extra virgin olive oil and avocados are excellent sources for monounsaturated fatty acids.

The same is true for butter and lard. When feasible, we encourage to get them from grass-fed animals because this encourages smaller scale decentralized agricultural practices more in-line with sustainable practices. Furthermore, but they also have a slightly higher content of omega-3 fatty acids – which certainly won’t cause harm and may even be healthful.

Polyunsaturated fatty acids

Science Corner

PUFAs contain two or more double bonds (C=C). The two we hear about most often are the plant-derived omega-3 fatty acid alpha-linolenic acid (ALA) and the omega-6 fatty acid linoleic acid (LA) that comes from both plants and animals. Neither ALA nor LA are strictly essential contrary to what you may have heard!

This confusion stems from the fact that ALA can be converted to the active animal forms called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). And LA can be converted into the omega-6 fatty acid called arachidonic acid (AA). However, the conversion rates are too slow to support normal healthy physiology long-term [11].

Say you eat 2.5 g of plant-derived omega-3 fatty acid (ALA), how much of the active forms EPA and DHA will your body end up with? You’ll convert a paltry 6% into EPA (0.15 g) and 3.8% into DHA (0.095 g) [12]. And these are best case scenario estimates for people eating lots of saturated fat. If we estimate the conversion loss based on people eating a lot of seed oils (high PUFA diet) then those figures nearly get cut in half!

So if some PUFAs are essential, can they be bad for you? Yes! We know this is counter-intuitive, but please bear with us.

One of the main problems is that PUFAs are not very stable and should be avoided for cooking (high or low heat); they are best consumed raw in whole food sources like salmon. PUFAs are also prone to rancidity which turns them somewhat toxic. Omega-6 fatty acids are especially problematic because their rancidity is hard to notice. Unlike omega-3 fatty acids, omega-6 fatty acids don’t emit a distinctive smell when they go rancid.

It’s also important to note that despite being an essential fatty acid, too much of them can be harmful and cause inflammation, as is the case with linoleic acid (LA). Moreover, consuming seed oils which are full of PUFAs is linked to increased risk of common western diseases such as cardiovascular disease, obesity, diabetes, cancer and more.

Many of the highly processed industrial seed oils are rich in LA and other omega-6 fatty acids. It’s best to be cautious of omega-6 fatty acid intake, as the typical standard American diet is often highly imbalanced when it comes to omega-6 to omega-3 ratio. The ideal ratio is close to 1:1, up to 4 or 5:1, thereabouts [13]. In the typical western diet the ratio can skyrocket up to 30:1 [14]!

Optimal fat intake with Nutrita

Nutrita helps you choose foods that both work towards your long-term goals and are genuinely tasty. Following a ketogenic diet with Nutrita makes it easy to get the hard things right, like optimizing your omega-3 to omega-6 ratio.

Our rule of thumb is: don’t worry about getting lots of omega 3’s but instead focus on diligently avoiding seed oils that are major sources of omega 6. Nutrita helps you with the hardest part; figuring out the ‘hidden’ sources of seed oils, like in industrial sauces or most brands of mayonnaise.

Even if your goal is to lose fat, don’t be afraid of eating fat. Simply be mindful of avoiding industrial sauces that have seed oils hidden in them. If you’re out at a restaurant don’t hesitate to ask what fat they used to cook your food in. Yeah, it’s annoying to have to ask, but your health is worth the hassle.

Again, don’t fear fat. Afterall, fat is the primary source of energy on a ketogenic diet, whether coming from your plate or belly. Yes, 1 gram of fat has more than twice as many calories as do protein or carbs, but we care more about how it affects fuel partitioning than we do its caloric content. Fuel partitioning is a fancy way of saying what your body decides to do with the food; shunt more of it towards growing your muscles or growing your fat stores? That’s the balance that matters. The caloric balance simply follows on from that. People getting the causality upside down.

Remember, fat loss is about biology, not physics. And no, we’re not saying calories don’t matter on a ketogenic diet – they do. But if your diet is low-carb and low-fat, it is also low-calorie. That sounds an awful lot like chronic caloric restriction that failed for most people most of the time. What bodybuilders do for competition prep is another question that we’ll leave aside for now.

The keto score will help you to stay in ketosis and achieve the right macronutrient mix while feeling full and sticking to nutrient dense food. Our insulin index will help you avoid carby junk-food which also happens to be chock full of nasty seed oils – a double win!

Fat distribution in food

wild slamon and beef are good fat source. Mayonnaise and French fries are bad fat sources rich in trans-fats

Most foods contain a mixture of many different kinds of fats. For this reason, it’s challenging to remember what type of food includes what kind of fat. Interestingly though, most people who still think that saturated fat causes atherosclerosis don’t even know in what kind of food it occurs in!

Lard, for instance, doesn’t have a stellar reputation. This is despite the fact that more than 50% of fatty acids in lard are unsaturated, mostly coming from oleic acid, the monounsaturated fatty acid that is also found in olive oil (more than 60% of it) [15]. It’s linked to many positive health benefits. Most people who demonize lard certainly don’t realize that it consists largely of the fatty acids that they praise for their health benefits when it comes from more ‘acceptable’ sources.

The only foods in which the percentage of saturated fat exceeds unsaturated fat are coconuts and dairy products. While this may seem frightening, it’s not a problem. In fact, an association study found that dairy consumption is associated with decreased cardiometabolic disease mortality [16].

I will never understand how meat became associated with being the primary source of saturated fat. First of all, the majority of meat that we eat is very low in total fat. For example, the average steak contains about 5% fat [17]. There are fattier cuts like pork belly and ribeye steak that people enjoy, no less because of fat’s ability to literally transport flavor. Most of us however, mistakenly avoid the parts of the animal that are high in fat, such as the brain and the fattier cuts of meat. Do you know anyone who eats brain (except for Nutrita’s co-founder Raphael…)? Clearly, fatty cuts are thought to not be good for our heart health by most people. It may surprise you though that meat is actually higher in unsaturated than saturated fat – who knew?

Interestingly, 100g of fatty fish such as mackerel contains a little less monounsaturated fat (5.5g) than a ribeye steak does (6.5g) [18,19]. You’ve already heard that beef should be avoided because it contains too much saturated fat, right? Besides that, fish is an essential source of the omega-3 fatty acids DHA and EPA. Because these are rarely obtained in adequate amounts through non-animal dietary sources, it’s smart to eat fish once or twice per week.

Nuts also mostly contain unsaturated fats and are an excellent source of healthy fats. The same is true for avocados, of which 85% is unsaturated, most of it being monounsaturated [20].

Sources of healthy fat

here is a list of healthy fat sources, avocado, red meat, fish, eggs, coconut, bacon, pistachio, nuts, dark chocolate, olive oils, chees, greek yogourt

I have to admit that the science on fatty acids is pretty complicated. In this whole jungle, how are you supposed to remember which ones are good and which ones bad? First off, Nutrita is here to help you. Second, as a rule of thumb, always answer the question:

does it come from a simple animal sources or is it an industrially concentrated plant product?

Fat from animal sources (e.g. beef trimmings, butter, lard) are generally good. Fat from plant sources (e.g. flax oil, sunflower oil, soybean oil canola oil) are notably bad. There are exceptions though, like olive oil, avocado oil and palm oil (environmental concerns for the latter notwithstanding).

Whole-food products we’ve evolved to eat to differing degrees such as meat, fish, olives, nuts and seeds all contain fats conducive to health. Dairy products are a recent addition to humanity, but unlike other novel additions such as grains, many of us seem to tolerate them well for the most part. Dairy is one of those things you should experiment with removing and reintroducing.

While you may think butter is a ‘processed product’ (it is, technically) and therefore not good, you’d be wrong. When you use it for flavor and cooking, it’s fine, but when it takes over meat fish or even vegetables – I’m looking at you Bulletproof Coffee – then it stops being health promoting.

By the way, ever tried to isolate the oil from sunflower seeds by hand? Good luck! This requires a lot of sophisticated industrial machinery that damages the fragile unsaturated fatty acids making them all the more noxious to your health.

Fats to avoid

Fats to avoid are canola oil, sunflower oil, chips, pizza, mayonnaise, french fries

One kind of fat that must be avoided no matter the type of diet you follow are industrial trans fats. Trans fats are made by the hydrogenation of unsaturated vegetable oils. Ruminant derived trans fats (from a cow) like CLA are fine.

Trans fats were introduced in the 1950s to make liquid vegetable oils solid at room temperature. This made them more stable, leading to a longer shelf life and a cheaper price tag. Trans fats also occur naturally in small amounts in dairy and meat, but it is the industrial kind of trans fats that you should avoid. They are known to cause heart disease and strokes and are also associated with an increased risk of type 2 diabetes [21, 22]. Trans fats are found in fried foods such as donuts, ready meals like frozen pizza, biscuits, cookies and crackers, and in margarine.

The science behind the harmful effect of industrial trans fats is so robust that their use is even restricted in some countries (Denmark, Switzerland, and Canada) and states (California, New York State, Baltimore, and Montgomery County) [23, 24]. The U.S. Food and Drug Administration categorizes them as not being GRAS (Generally Recognized as Safe). These kind of foods are usually not part of a well-formulated ketogenic diet that Nutrita would help you follow. Our app takes out the guesswork of you figuring out if this or that food is full of trans fats.


Thankfully, it just so happens that diets which exclude flours and refined sugars also tend to exclude most sources of nasty seed oils. These 3 ingredients – flour, refined sugars and seed oils – are mixed together in many different ways to give you lots of different junk-foods, like pizza, donuts or loaves of bread.

By avoiding this sort of junk-food you’ve effectively drastically lowered your omega-6 fatty acid intake (LA and AA) as well as your intake of unsaturated oxidized oils. How much omega-3 fatty acids you need is comparatively much less important.

Nevertheless, some people may need to focus on increasing omega-3 fatty acid on top of eliminating seed oils from their diet for specific medical conditions. Eating lots of fatty fish like mackerel and sardines for instance is a good strategy to do so, probably better than gambling on dodgy fish oil supplements.

So stick to the basics of eliminating the ‘worst offenders’ from your diet and you’ll reap most of the benefits.

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Written by Sarah Neidler, PhD

Sarah Neidler did her PhD in cancer research at the Beatson Institute for Cancer Research in Glasgow. She has a strong interest in nutrition and the ketogenic diet and believes that they are beneficial for the treatment and prevention of chronic conditions, such as heart disease and diabetes. She loves cooking, reading, sewing, Yoga, and CrossFit.

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