15 Worst Cooking Oils for Your Thyroid

By |2018-06-01T07:03:25-07:00June 7th, 2017|Hypothyroidism, Nutrition|18 Comments
  • worst cooking oils

This is a very important but confusing topic that has a much bigger impact on your thyroid than you realize.

There is a lot of confusing and false information that continues to circulate across the globe regarding what fats and oils are truly healthy.

Unfortunately, you and millions of other people have been led to believe that all of these so called “heart healthy” oils in your diet are preventing future health problems… while the reality is that they are not only heart UN-healthy, but are also linked directly to hypothyroidism.

I’ll show you how in just a minute.

One of my favorite quotes that I find applicable to many situations in life, including this one, is…

Going all the way back to 1960’s, the entire “heart healthy” marketing movement was driven by the fact that polyunsaturated fats (PUFAs) could lower cholesterol.

Even though the “heart healthy” movement is still going strong today, the entire cholesterol myth has been debunked by science long ago.

(NOTE: Want to learn the truth about hypothyroidism, cholesterol, and heart disease? Take a look at this post on “Why “Bad Cholesterol” Is Essential to Your Thyroid“.)

If all of these polyunsaturated fats were so “heart healthy”, then why has heart disease continued to rise in spite of our drastic increase in the use of these oils?

According to statistics from the FDA, our use of “heart healthy” polyunsaturated oils has increased by more than 330% since 1970 with the average person today consuming 51.9 lbs. per year as opposed to only 15.4 lbs. per year in 1970.

If, over the course of 40 years, these “heart healthy” oils have not made a positive impact on heart health, then why does the medical system continue to push them as if another 40 years might provide some different results?

That’s not wishful thinking… As Albert Einstein would say, that’s pure insanity.

The truth is that these “heart healthy” (PUFA) oils are making an impact on heart disease… they’re just making it worse…

Take this PUFA heart health study for example:

Use of dietary linoleic acid [PUFA] for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis.


“In this cohort, substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, coronary heart disease, and cardiovascular disease. An updated meta-analysis of linoleic acid intervention trials showed no evidence of cardiovascular benefit.”

The study results show the following:

  • 62% increase in all-cause mortality (premature death)
  • 70% increase risk of cardiovascular disease
  • 74% increase risk of coronary heart disease.

Those aren’t slight increases. That’s a huge problem!

That doesn’t paint a good picture for polyunsaturated fats, but believe it or not, polyunsaturated fats can paint a good picture, so to speak…

PUFAs – Great for Paint… Bad for Hypothyroidism

Polyunsaturated fats were once used almost exclusively for paint varnish.

You see, polyunsaturated fats work great for paints because they oxidize and dry very easily, allowing paint to be liquid and then dry when applied to a wall.

But, somewhere between the lines of ignorance and “insanity”, as Albert Einstein would have said, we’ve completely ignored the obvious dangers of these fats in favor of unscientific research and false promises.

It is very well known that polyunsaturated fats oxidize rapidly when exposed to oxygen and heat, and this oxidation creates free radicals, oxidative damage, and cell death.

Killing your own cells definitely doesn’t improve your health, in case you were wondering.

Regardless of how these oils are processed and manufactured, oxygen is abundant in the human body which is heated to roughly 98.6 °F.

Needless to say, your body is a perfect environment for the oxidation of polyunsaturated fatty acids.

But that’s only part of the problem…

Polyunsaturated fats also promote and cause hypothyroidism on multiple levels by blocking every part of your thyroid hormone pathway.

  1. Polyunsaturated fats block the thyroid gland from releasing thyroid hormone.
  2. Polyunsaturated fats block the transport of thyroid hormone to your cells within your bloodstream.
  3. Polyunsaturated fats block your liver from converting T4 thyroid hormone into the active T3 form of the hormone that your cells need.
  4. Polyunsaturated fats block your thyroid hormone from binding to your cell receptors.
  5. Polyunsaturated fats block your cells from properly utilizing the thyroid hormone that is available.

(NOTE: Want to learn some some ways to start fixing your thyroid hormone pathway so you can start seeing results with your hypothyroidism? Download our proven 3 Food Triple-Thyroid Boosting Protocol now and learn how to start every day right, feeling calm, clear, and full of energy.)

The Simple 3 Food Triple Thyroid-Boosting Daily Protocol

You can download this daily protocol here.

15 Worst Cooking Oils for Your Thyroid

The only way to stop the thyroid-suppressive effects of most cooking oils is to avoid them altogether.

Unfortunately, this is difficult because these toxic oils are so inexpensive. So, people continue to use them in their kitchens. And they are used almost exclusively in restaurants and in commercial food products where inexpensive oils lead to greater profits.

Below are fifteen of the worst oils/fats that pose the greatest risk to your thyroid based on their ratio of polyunsaturated fat (PUFA) to saturated fat.

Here they are ranked in order, starting with the worst:

  1. Safflower Oil
  2. Grapeseed Oil
  3. Flaxseed Oil
  4. Walnut Oil
  5. Vegetable Oil
  6. Canola Oil
  7. Corn Oil
  8. Soybean Oil
  9. Sunflower Oil
  10. Sesame Oil
  11. Almond Oil
  12. Cottonseed Oil
  13. Peanut Oil
  14. Shortening
  15. Avocado Oil 

When Will the Insanity End?

How much longer do they have to keep repeatedly pushing and promoting the use of these oils before we realize that ignoring the science that is right in front of our eyes is true insanity?

By continuing to follow the health advice of the masses, how can you logically expect different results? How can you expect anything but more hypothyroidism, heart disease, and cancer?

Sometimes the only way to achieve opposite results is to take opposite action.

Do yourself a favor, and if you use any of these worst cooking oils, then stop and replace them with a fat known to help support healthy thyroid function.

You can learn more about one thyroid-boosting fat I highly recommend you use instead in our 3 Food Triple-Thyroid Boosting Protocol.

Click here to get started with your 3 Food Triple-Thyroid-Boosting Daily Protocol.

About the Author:

Tom Brimeyer is the founder of Forefront Health and the creator of the popular Hypothyroidism Revolution program series. Specializing in thyroid and metabolism disorders, Tom's work has impacted over 50,000 people spanning more than 60 countries. Tom is also a highly sought after practitioner who runs a successful health consulting practice where he continues to help clients across the globe to take back control of their lives from their devastating health conditions.


  1. Sara June 8, 2017 at 9:32 am - Reply

    What is wrong with Avocado oil?
    You can’t cook with Olive oil in high temperatures, but Avocado oil is okay to use in high temperatures.

    • Tom Brimeyer June 8, 2017 at 10:54 am - Reply

      Hi Sara, as mentioned in the article it has an unsatisfactory polyunsaturated to saturated fat ratio, which can suppress thyroid function.

  2. Shauna June 8, 2017 at 11:29 am - Reply

    So coconut oil would be ideal when an oil is needed?

  3. Lisa R. June 8, 2017 at 11:44 am - Reply

    Gosh, I wish I knew that before I bought a big expensive bottle of avocado oil!!!

  4. Babs June 8, 2017 at 11:47 am - Reply

    So this list would be the same for unhealthy uncooked oils?

    • Tom Brimeyer June 8, 2017 at 12:03 pm - Reply

      Hi Babs, it doesn’t matter if it’s cooked or not. The article mentions that oxidation can occur even at body temperature.

  5. Emma June 8, 2017 at 2:54 pm - Reply

    Oh, I love pumpkin seed oil and use it loads! A good choice or no?

    • Tom Brimeyer June 8, 2017 at 3:01 pm - Reply

      Hi Emma, a general rule of thumb is if it comes from a seed, then it’s going to be predominantly PUFA.

  6. Grace June 8, 2017 at 4:36 pm - Reply

    Hello, Is olive oil included on this list as a vegetable oil?

    • Tom Brimeyer June 8, 2017 at 5:18 pm - Reply

      Hi Grace, olive oil isn’t on the list. Vegetable oil refers to the cheap vegetable oil that you’ll find at most grocery stores. It typically a mixture of canola, soy, and safflower oils.

  7. Kolleen June 8, 2017 at 5:18 pm - Reply

    I use coconut oil to cook but I use olive oil for my salad dressing which I eat everyday. I don’t see it on the list. How does it rate?

    • Tom Brimeyer June 8, 2017 at 5:19 pm - Reply

      Hi Kolleen, that’s perfectly fine.

  8. Shasha June 8, 2017 at 10:02 pm - Reply

    Yes…raw walnuts made my weight go up, but I need to eat them. They are 1/3 of my diet..can’t eat much else. They are my source of fat besides organic poached eggs. They are very healthy. I can’t eat saturated/monounsaturated fat… clogs my blood vessels. Heated oils hurt me..make free radicals. I can’t avoid this oil.

    • Tom Brimeyer June 9, 2017 at 6:21 am - Reply

      Hi Shasha, I think you missed some important points in the article. Saturated fats don’t clog arteries or increase your risk of heart disease as per the study mentioned. High levels of PUFAs do.

  9. Sue June 29, 2018 at 6:22 am - Reply

    I was using coconut oil since i know it the best to use , but i end with high cholesterol and my nutritionist said don’t eat it at all, because it was behind my high cholesterol .She was right when i stopped and did blood test after 4 month was OK my cholesterol .
    There is good article about coconut oil and cholesterol on line ,google it ,
    Was is your reading Tom about this ?

  10. Debbie T. April 7, 2021 at 6:53 pm - Reply

    Hi Tom,
    I use La Tourangelle Organic Sun Coco Oil for some cooking and baking because it’s a very neutral tasting oil. It’s a blend of high-oleic sunflower oil and refined coconut oil (both organic). From research it seems that high-oleic sunflower oil is pretty low PUFA. The nutrition label says:
    Saturated Fat 3g
    Trans Fat 0g
    Polyunsaturated Fat 2g
    Monounsaturated Fat 9g

    How does that look for composition? Otherwise I occasionally use olive oil; for other cooking needs I use organic ghee, Kerrygold butter, or organic refined coconut oil. Thanks for all you do!

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