Concerns with Polyunsaturated Vegetable Oils – Part 2

This article is Part 2 in a two-part series on concerns with Polyunsaturated Vegetable Oils.Part 1 can be read here.

There are a few key things about polyunsaturates vegetable oils that need to be understood to understand this article, so I’ll keep the science simple.

There are two class of polyunsaturated fats; (PUFAs); omega 3 (ω-3 also written n-3) and omega 6 (ω-6 / n-6) which compete with each other for enzymes, and which becomes significant at one branch point (marked with the red and green box).

At that junction point (where the red box is at Arachidonic acid and green box is at Eicosapentanoic acid) if there is more n-6 fats than n-3 fats, then the pathway will favour the n-6 pathway. If there are more n-3 fats than n-6 fats, then the pathway will favour the n-3 pathway. The issue, as I will elaborate on below, is that in the Western diet, the n-6 pathway is always favoured.

Of significance, the n-6 polyunsaturated fats are pro-inflammatory and the n-3 polyunsaturated fats are anti-inflammatory. This is important to understand why eating lots of foods high in n-6 fats can lead to health consequences.

When people take low-dose Aspirin® for example, to lower the risk of heart attack or stroke, it acts on Arachidonic acid in the n-6 polyunsaturated fat pathway, to keep it from making certain inflammatory products that can lead to heart attack or stroke. 

In our evolutionary history it was thought that n-6 fats (from nuts and seeds that were gathered in the wild) and n-3 fats (from the fish and meat we hunted) were eaten in close to a 1:1 ratio – providing the two essential fatty acids from both classes. When man began domesticating grain and growing beans and lentils and nuts and seeds for food (all high in n-6 fats), the shift towards a diet higher in n-6 fats occurred. The modern Western diet is estimated to have an omega-6 to omega-3 fatty acids of 15–20:1 in favour of n-6 fats [6].

Many people take omega-3 fish oil capsules in an effort to protect their body from inflammation, but because the amount of n-6 fats in the diet is so much higher than the amount of n-3 fats, the n-6 pathway is still favoured.

Unless we significantly lower the amount of n-6 fats in the diet, taking fish oil doesn't really help as the n-6 pathway will always be favoured.

Changing the Makeup of Cell Components

Industrial seed oils have very high levels of linoleic acid which is at the top of the n-6 pathway.  These industrial seed oils are pro-inflammatory and will elongate to Arachidonic acid, resulting in many pro-inflammatory products being produced.

When we eat a lot of food made with soybean oil or fried in soybean oil we eat way more linoleic acid then our body has evolved to handle.

A major problem with polyunsaturated fatty acids such as linoleic acid are that they are very unstable fats that are easily oxidized (similar to a fat becoming ‘rancid’ or a metal ‘rusting’). Even if we never buy these industrial seed oils to cook with at home, when we buy French fries at restaurants they are fried in either soybean or canola oil. When we pick up a donuts, same thing.  Bottle salad dressing and mayonnaise (even the one that is called ‘olive oil mayonnaise’) are made with one of these industrial seed oils. These oils are found in products one would never expect to find them, including peanut butter! Start reading labels and you will be shocked how many products they are in – or rather, how few products they are NOT in.

Industrial seed oils are in most of the prepared food we buy and almost all of the food we eat out in fast-food restaurants.

According to a 2011 journal article published in the American Journal of Clinical Nutrition;

“The most striking modification of the US food supply during the 20th century was the >1000-fold increase in the estimated per capita consumption of soybean oil from 0.006% to 7.38% of energy.” [7]

When the linoleic acid content of the diet is high because we are eating foods made with industrial seed oils, important components of our cells membranes incorporate higher amount of linoleic acid into them.

For example, cardioleptin is a phospholipid component found in the inner mitochondrial membrane, which is where all energy metabolism in our body occurs. Cardioleptin plays an important role in the function of several enzymes involved in mitochondrial energy metabolism. 

When we eat a lot of pre-made and processed foods and food made in fast-food restaurants, cardioleptin’s fatty acid content becomes 90% linoleic acid, making it easily oxidized, affecting its function. If the diet is high in coconut oil and olive oil, cardioleptin will be higher in stearic and oleic acids and these fats are more stable fats than linoleic acid.

Literally, we are what we eat!

Cooking with Industrial Seed Oils

When industrial seed oils are heated such as they are in the making of commercial foods using them, they undergo rapid oxidation which means that they react with oxygen in the air to form toxic substances, including aldehydes and lipid peroxides.  Aldehydes are known neurotoxins and carcinogens, and are documented to contribute to DNA mutations, inflammation and hypersensitivity [8].

Heating polyunsaturated vegetable oils for just 20 minutes produces 20 times the permitted levels of ldehydes recommended as a maximum limit by the World Health Organization [8].

Keep in mind that at fast-food restaurants and in the preparation of commercial donuts and other fried food products, these industrial seed oils are used for frying everything from French fries to donuts and are heated over and over for extended periods of time, creating alarming levels of aldehydes and lipid peroxidation products.
Concentrations of aldehyde per litre of oil when heated to 180 C (from Groosvelt et al, 2015)

When heated, industrial seed oils produce oxidized metabolites known as oxidized linoleic acid metabolites (OXLAMs) which have been also been implicated in the development of non-alcoholic fatty liver disease (NAFLD)[9].

In the body cell components such as cardioleptin with high amounts of linoleic acid are easily oxidized producing an oxidation product known as 4-hydroxynonenal (4-HNE) which has been implicated in the development of cancer [10].

Increasing Appetite

The high linoleic acid content of industrial seed oils also act on two endo-cannibinoids in the body (2-AG and Anandamide) which results in us feeling hungry, even when we have recently eaten –  in much the same way as cannabis (marijuana) does [11-12].  As a result, these industrial seed oils are believed to contribute to obesity and the associated health risks such as Type 2 Diabetes and high blood pressure.

Final Thoughts…

For fifty years, the public ate industrially-created trans fats in place of natural saturated fats and we only found out later that they were a major contributor to heart disease.

For the last forty years we have been eating industrial seed oils in greater and greater quantities place of natural saturated fat, but (a) given how these industrial seed oils are produced (solvents, high heats for extended period of time, bleach, etc.) and (b) given what is known about the very toxic products they produce when heated in production and how they are oxidized in the body and oxidized through heating when cooking, it is warranted to be very cautious about eating prepared foods made with them.

To avoid these industrial seed oils will take a concerted effort as they are in virtually everything we buy ready-made and many of the foods we eat out, but one solution is to cook real food using healthy sources of fat and to avoid these industrial seed oils that were created and marketed to us as supposedly healthy substitutes for natural fats.

The butter, lard and tallow of years gone by were made from animals that were pasture raised, not fed soybeans and corn as commercial animals are now, but in light of the mounting number of studies that indicate that saturated fat is not associated with increased risk of cardiovascular disease, perhaps it might be preferable to buy grass fed butter or render tallow or lard from the fat of pasture-raised animals for some cooking applications – rather than use these industrial seed oils that were created as substitutes.  Butter, lard and coconut oil (a vegetarian saturated fat) are all very low in linoleic acid and thus are very stable.  They are not easily oxidized in the body or by heating and produce very low levels of aldehyde and lipid peroxidation products when heated, compared with many of the industrial seed oils.

These are all factors we need to consider when deciding which fats our food should be made with.

The chart below shows the linoleic content of some common fats in blue.  Keep in mind that fats with the smallest amount of linoleic acid are the most stable and the least prone to oxidation (either in the body or when heated).

Comparison of Dietary Fats – linoleic acid content
A personal note:

For non-heating uses, I use natural sources of monounsaturated fat such as cold pressed macadamia nut oil, hazelnut oil, avocado oil, and extra virgin olive oil and for cooking and heating uses I use a mixture of olive oil and coconut oil (to raise the smoke point), clarified butter (ghee) at higher temperatures and butter at lower temperatures and for baking.

I read labels of all products I buy and deliberately avoid purchasing any food products that contain soybean oil, canola oil or sunflower oil and when I eat out, I ask that my food be prepared with coconut oil, butter or ghee.

While the jury is still “out” when in comes to saturated fat, it is my opinion that with the mounting evidence that eating saturated fat does not contribute to heart disease, using moderate use of butter, ghee (clarified butter) and coconut oil seems to me to be a more acceptable risk than eating foods made with, or fried in industrial seed oils.

I trust having the information contained in this article will help you make an informed choice for yourself and for those you cook for.

If you have questions about how I might be able to help you follow a low carb lifestyle -including selecting appropriate fats for use in your own cooking, please feel free to send me a note using the “Contact Me” form located on the tab above.

References

(continued from Part 1)

6. A.P. Simopoulos, Evolutionary aspects of the dietary omega-6:omega-3 fatty acid ratio: medical implications,World Rev Nutr Diet, 100 (2009), pp. 1-21

7. Tanya L Blasbalg, Joseph R Hibbeln, Christopher E Ramsden, Sharon F Majchrzak, Robert R Rawlings; Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century, The American Journal of Clinical Nutrition, Volume 93, Issue 5, 1 May 2011, Pages 950–962.

8. Grootvelt M, Rodada VR, Silwood CJL, Detection, monitoring, and
deleterious health effects of lipid oxidation products generated in culinary oils during thermal stressing episodes, Lipid Oxidation, November/December 2014, Vol. 25 (10)

9. Maciejewska, Dominika & Ossowski, Piotr & Drozd, Arleta & Karina, Ryterska & Dominika, Jamioł & Banaszczak, Marcin & Małgorzata, Kaczorowska & Sabinicz, Anna & Wyszomirska, Joanna & Stachowska, Ewa. (2015). Metabolites of arachidonic acid and linoleic acid in early stages of non-alcoholic fatty liver disease-A pilot study. Prostaglandins & other lipid mediators.

10. Zhong H, Yin H. Role of lipid peroxidation derived 4-hydroxynonenal (4-HNE) in cancer: Focusing on mitochondria. Redox Biology. 2015;4:193-199. doi:10.1016/j.redox.2014.12.011.

11. Alvheim AR, Malde MK, Hyiaman DO et al; Dietary Linoleic Acid Elevates Endogenous 2-AG and Anandamide and Induces Obesity, Obesity (2012) 20;1984-1994

12. Alveim AR, Torstensen BE, Lin YH et al, Dietary Linoleic Acid Elevates the Endocannabinoids 2-AG and Anandamide and Promotes Weight Gain in Mice Fed a Low Fat Diet, Lipids (2014) 49:59–69


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Author: BBDN

Joy Y Kiddie MSc., RD - I'm a Registered Dietitian in private practice in British Columbia, Canada that provides services in-person in my Coquitlam office, as well as by Distance Consultation (using Skype / telephone).