Oils For Cooking: Which Ones Should You Avoid?

by The Health Sciences Academy — Get free science updates here.

First of all, you don’t need to be a chef to benefit from today’s article. I’ll answer a common question so when your client asks, you’ll be able to give them the best information possible.

Let’s run a little test:

  • Which oils are you (or your client) cooking with?
  • Why are you (or your client) using those oils?
  • Do you think there are better options?
  • And which oils do you believe you should avoid?

When it comes to cooking, not all oils are created equal.

Here’s the bottom line: some oils are better suited for cooking than others.


Simply because they can handle the heat better, making them less dangerous to your health. And that’s a big deal, especially when using higher heat.

With that in mind, the context of today’s article is the toxicity, oxidation, release of free radicals, and degradation of oils for cooking (rather than heart health, or weight loss, or everything else under the sun).

Smoke points and harmful free radicals

The first question you need to ask yourself is: which oils create harmful compounds when heated?

Let’s start with the smoke point first.

The smoke point of an oil is the temperature at which it goes over the edge of safety and starts smoking.

When an oil is heated past its smoke point, it releases free radicals – it reacts with oxygen to form harmful compounds. You definitely don’t want to be consuming or breathing in these.

Free radicals can injure cells and DNA in your body.

Beware of HNE, a nasty compound

One harmful compound that can be produced when heated is called HNE. This compound is linked to the pathogenesis of vascular diseases such as atherosclerosis, diabetes, and neurodegenerative disorders.

The nasty thing with HNE is that the longer you heat the oil, and even the more you reuse that oil, like restaurants do, the more HNE it will accumulate.

Bad for the body.

Plus, when it comes to oil reuse, this is a great opportunity to truly limit your eating of fried foods, especially in restaurants. Restaurants commit two bad acts:

  1. they typically fry in polyunsaturated fats (you’ll learn why this is not ideal in a moment) and
  2. they reuse the oil over many times.

Keep in mind that our human body is quite capable of defending itself from toxic or unsafe compounds that enter its space. The best line of defence that you can consciously choose for your well being is to minimise exposure to noxious compounds such as these.

Oil stability is revealed in saturation levels

Regarding the saturation level of fats in cooking oils, consider the types fatty acids they have. This will give you a big clue in both their heat tolerability and overall stability.

Oils with saturated fatty acids are the top choice for cooking. These oils include coconut oil, clarified butter (ghee), butter, and palm olein (refined palm oil).

They are stable because the fatty acids are basically packed tightly together. They’re not loose, in other words. They can tolerate high heat well.

At the other end, there are oils with polyunsaturated fats. These are oils like soybean, corn, canola, sunflower, and safflower. They’re unstable fats – they’re not bound together tightly at all. Because they are unstable, they can produce higher levels of free radicals when they’re heated.

And, as we said before, we don’t want too many free radicals in our bodies.

What is ‘high heat’ cooking… and why should I care?

Higher heat cooking is used for sautéing, frying, stir-frying, grilling, pan roasting, searing and caramelising.

The real big important consideration here is: what happens to the oil when it gets too hot? This is where you want to be considerate of the type of oil you’re using.

When it comes to using oils for cooking, you have choices to decide upon.

As mentioned previously, you can use oils with stable fats, such as olive oil, avocado oil, clarified butter (ghee), refined palm oil, and coconut oil. This is a healthier way to heat your foods, because oils with saturated fats are pretty resistant to heating, which means less degradation.

The oils which should be avoided for cooking are oils like soybean, corn, canola, sunflower, and safflower. These oils have unstable fats and will decimate the nutritional properties of your food. Oh, and they’ll give you a big fat health risk in the meantime.

Cooking with oil 101

Heating oil up until it smokes is a really bad idea anytime if you want to keep things healthy.

Here’s a scenario that you or your client might be able to relate to:

You turn on the heat on the stove top, put some oil into your pan and get distracted by something outside the kitchen. Next thing you know smoke is everywhere.

Sound familiar?

If you’re cooking at high heat for say sautéing, grilling, or pan searing, the salient point to remember is to use oils that are stable and have a high smoke point.

That means they have more stable fats, or saturated fats, in them to tolerate the high heat better. I’ll give you a complete list below so you can be clear.

Okay, in summary, which oils should you use?

Based on the above, here are the best cooking oils to use in the kitchen in order to reduce free radical exposure and toxicity.

The simplest way to break this down is by the level of cooking heat you are using.

This first group is for high-heat cooking. These are specifically for frying, sautéing, grilling, pan roasting, searing, stir-frying, and caramelising. Here are a few safe choices:

  • light or refined olive oil (here the word ‘refined’ means without the combustible solids found in extra virgin oil, which can degrade into harmful oxidation products during high-heat cooking)
  • avocado oil
  • clarified butter (ghee)
  • refined palm oil (here the word ‘refined’ also means without combustible solids)
  • coconut oil

All of the above have a higher smoke point and are lower in polyunsaturated fats.

If you are leaning towards just medium-heat cooking, such as gentle sauté, stewing, baking, or braising, all of the above would work, as well as butter.

Free Download

Click HERE to get our Oils For Cooking Workbook (PDF download) that will help you work out if the oils you're currently using are suitable or not.

Remember, for both high-heat and medium-heat cooking, look for a cooking oil that meets both of the following criteria:

  1. LOW percentage of polyunsaturated fats (15% or below), and
  2. HIGH smoke point (160 °C or above).

How about off-heat options, such as over a finished dish, after it's been cooked?

For maximum flavour, you can go for unfiltered extra virgin olive oil and unrefined or toasted nut and seed oils.

Care for your oil: avoid these two things

When taking care of your cooking oils, there are two additional things to remember (besides heat and saturation). These two things are:

  1. oxygen, and
  2. exposure to light.

Why? Because they negatively affect the oils and can cause them to become rancid.

Rancid oils are a major source of destructive free radicals in our diet and they shouldn’t be consumed.

So, what should you do then?

Store your oils in a cool, dry place, away from direct light. You don't want them to oxidise and go rancid.

Also avoid buying in large containers. Buy smaller batches, so the oil has less 'sitting around' time and stays fresher.

Oh, one more thing – tighten that lid before storing to keep them cared for best!

Your Next Steps

Do you want to discover how you, or your clients can eat healthy? Do you want to learn how to build personalised food plans that you or your clients can follow? Or would you like to help them understand how their genetic makeup can be adapted to nutrition and how food can change their DNA?

Getting specialised by completing our Nutritional Therapist Certification can be your first step towards acquiring the unique knowledge and skills for helping you or your clients make the necessary changes to their diet and lifestyle, in a way that is personalised.

You will also learn:

  • How to perform client assessments and detect nutrient deficiency risks
  • How to structure client consultations
  • About free radicals and DNA damage
  • How to test your antioxidant capacity and so much more!

Get started now and start expanding your knowledge and building your future in nutrition.

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The-Health-Sciences-Academy-Alejandra-Ruani-small1-right Alex Ruani, Doctoral Researcher, is the Chief Science Educator at The Health Sciences Academy, where her team of accomplished scientists and PhDs are training a new breed of over 100,000 highly-specialised nutrition professionals who are leveraging the latest personalisation strategies to help their clients. She is a Harvard-trained scientist and UCL Doctoral Researcher who is fanatical about equipping health professionals with the latest science-based tools so they can succeed in their practices – from identifying the unique nutrient needs to building highly personalised nutrition programs. Besides investigating and teaching the latest advances in health and nutrition biochemistry, Alex makes it easier to be smarter with her free email updates.

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