Whole-Food PUFAs Are Not Better Than Seed Oils
This is not about food fear but about biological and evolutionary context
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Disclaimer: Content for entertainment purposes only. Not medical or health advice.
This article is inspired by a post I saw on Twitter (or X, as Mr. Musk would have you call it).
The Tweet in question argued for an increased intake of PUFAs (polyunsaturated fats) from natural sources, such as nuts and fatty fish, in the winter, citing an evolutionary perspective. Here is the summary of the post:
Seed oils are terrible not because of their PUFA content but because of the chemical process used to extract and deodorize them. You should not fear natural PUFAs.
You should eat more PUFAs in the winter, as cold-climate foods are higher in PUFAs.
PUFAs increase the body’s ability to produce more heat and stay warmer in the winter due to upregulating uncoupling proteins (UCPs).
I think that the topics covered in this Tweet are a good way to get a chance to dissect the many issues with PUFAs (not just with “seed oils”) and discuss why, just because PUFAs can help an animal in the wild survive a season of food scarcity (winter), it doesn’t make them (and their accumulation in tissues) optimal for health and longevity.
Disclaimer: This isn’t meant to spread food fear
Just to get this out of the way - acknowledging the many issues with PUFAs (including whole-food PUFAs) doesn’t mean that you need to become paranoid about their presence in foods to the point of starting to avoid anything that contains nuts, seeds or fish like the plague.
You will not drop dead if you eat a piece of pecan pie (unless you are deathly allergic to pecans, I guess) and having some salmon when the craving comes will not land you in a grave.
However, considering that the spirit of the post serving as inspiration for this article was all about insisting that we should be “PUFA-maxxing” in the winter, consuming as many nuts, seeds and fatty fish as possible during the cold months, I do find this article to be necessary to provide some clarity.
There’s a recurring sentiment that I have seen on health social media implying that, while industrially extracted “seed oils” are awful, their negatives can be circumvented by consuming whole-food, cold-pressed PUFAs.
While whole foods that contain PUFAs do have beneficial aspects to them (for example, seeds tend to be good sources of vitamin E and fish are great sources of protein, iodine, selenium, vitamin D, retinol and other nutrients), these foods’ PUFA content is not part of what makes them healthful.
To say that whole food PUFAs are better than “seed oil” PUFAs is very misleading and adds to the confusion. An excess of omega-6 and omega-3 PUFAs contributes to the same negative effects in the body regardless of source and regardless of whether or not they were oxidized before consumption (this will be elaborated on in more detail later in this article).
While there is no need to fear food, awareness of the different constituents of various foods (PUFAs, in this example) and a contextual understanding of their effects on health is important, especially when faced with content that encourages excessive PUFA consumption, regardless of source.
PUFAs 101
Since I have content that goes into this in-depth already, I’ll provide just a quick overview in this article for those who are not sure what PUFAs are.
Polyunsaturated fats (PUFAs, for short) are a type of fat with multiple double bonds. These double bonds can be thought of as weaker-than-normal links between the carbons that make up the fats. A PUFA fat can easily “break” or disintegrate in these places. My article on omega-3s goes into this in more detail.
Because of their structure, PUFAs create the perfect substrate for the generation of reactive oxygen species, leading to an increase in oxidative stress. They’re like kindling in a field of lit matches. A free radical (which is an unstable molecule that contains unpaired electrons in its outer shell) can easily “break” one of the double bonds to steal an electron from one of the polyunsaturated fatty acids. This process is called “lipid peroxidation,” and through it, more free radicals (as well as other reactive compounds) are created out of the injured PUFAs. This adds to the body’s oxidative stress burden and depletes our antioxidants.
The most common PUFAs found in foods are the omega-6 and omega-3 fats, referred to as “essential fatty acids.” In biology, the term “essential” means that the molecule in question is not synthesized by the human body. That definition differs from how “essential” is usually defined in plain English, meaning “indispensable.”
PUFA-rich oils tend to stay liquid in cold temperatures. An oil that consists mostly of PUFA will be liquid after being removed from the fridge. Oils high in PUFA include sunflower oil, safflower oil, corn oil, soybean oil, canola/rapeseed oil, cottonseed oil, and fish oil. Foods high in PUFA include most nuts and seeds and fatty fish, such as mackerel or salmon.
While omega-3s are often considered a fat that should be increased in the diet, they are even more prone to lipid peroxidation than omega-6 fats, and as you will see in this article, are even more problematic when incorporated into cellular components. This is because they have more double bonds. Their health benefits, as seen in numerous research studies, are mainly due to their ability to oppose the inflammation caused by omega-6-derived inflammatory mediators, such as prostaglandins. However, due to their ability to increase oxidative stress, a high omega-3 intake can ironically increase inflammation long term, as oxidative stress can stimulate the pathways responsible for the creation of inflammatory mediators such as prostaglandins, leukotrienes, and interleukin-1-beta. This is discussed in more detail in my article on omega-3s.
With a basic understanding of what PUFAs are let’s jump into the arguments being made in the Tweet.
“Seed oils are bad due to the extraction process and not because of their PUFA content. You should not fear natural PUFAs.”
“Seed oils” is a term used to describe the oils extracted from seeds, such as sunflower or rape seeds. In your supermarket aisle, “seed oils” would be the golden, liquid oils that are usually found in big, see-through plastic bottles. For the nutrition old-timers, these used to be called “vegetable oils,” before the term “seed oils” took off online.
These oils are popular in restaurant food due to their cheap cost and lack of flavour.
However, the very reason why these oils lack flavour and odour and are usually recommended for recipes that call for a “neutral” oil is due to the process through which industrial seed oils are produced.
This YouTube video is a decent illustration of the process but here’s the summary:
A solvent is often used to extract at least a portion of the oil. The most common one is hexane, which can convert into neurotoxic metabolites in the body.1 In order to be deodorized, the oils are steamed at very high temperatures and bleaching clay is used to remove impurities. High temperatures accelerate the oxidation of PUFAs, which can happen due to the presence of metal/mineral ions (which the clay is likely to contain). The use of bleaching clay has been shown to accelerate the oxidation of these fats.2
This process of course sucks and results in an oil with many lipid peroxides already in it.
However, the issue of lipid peroxidation and reactive oxygen species (ROS) generation remains even if these oils are consumed in their purest, unoxidized form in foods such as nuts or fatty fish.
Even if we eat completely intact and unoxidized PUFAs, they are likely to become oxidized and turned into highly toxic lipid peroxides such as malondialdehyde upon reacting with metals or proteins in the stomach.3
In the cell, instead of entering the mitochondria, PUFAs can be incorporated into cell membranes. This makes these cell membranes more prone to oxidative damage, which can injure and even kill cells.4
In the endoplasmic reticulum, the COX-2 enzyme can convert them (specifically the omega-6 PUFAs) into hormone-like molecules called prostaglandins, which cause chronic inflammation and pain, and interfere with cellular energy creation.56 High levels of prostaglandins (especially prostaglandin E2) are involved in many disease states. They are involved in causing painful periods,7 inhibited insulin release and diabetes,8 and the development and progression of cancers.9
In the mitochondria, PUFAs can get incorporated into mitochondrial membranes and components such as cardiolipin, instead of being burned for energy. This can make mitochondria more “leaky,” allowing protons to passively leak out, making it harder for the cell to establish the proton gradient needed to create energy (ATP).
Cardiolipin is a phospholipid found in the mitochondrial membrane and its job is to support energy production. One of its jobs is stabilizing mitochondrial complexes. In general, the more unsaturated the fats in cardiolipin, the more inhibited energy production becomes and the more ROS is produced. Increased cardiolipin unsaturation is a hallmark of aging.10
While it seems that cardiolipin still functions fine as long as it contains linoleic acid, reductive stress has been found to upregulate the enzyme delta-6-desaturase,1112 which converts linoleic acid to the more unsaturated fatty acid, arachidonic acid. When arachidonic acid gets incorporated into cardiolipin in place of linoleic acid, cardiolipin’s function declines.13 Reductive stress (caused by electrons moving too slowly through the mitochondria) is brought on by low metabolic function, which a high PUFA intake contributes to. Cardiolipin’s function declines further when the even more unsaturated fats, such as the omega-3 fat DHA, displace linoleic acid.1415 The content of fats in cardiolipin is reflected by the fats being consumed in the diet.
“At birth, the baby's mitochondria contain a phospholipid, cardiolipin, containing palmitic acid, but as the baby eats foods containing polyunsaturated fatty acids, the palmitic acid in cardiolipin is replaced by the unsaturated fats. As the cardiolipin becomes more unsaturated, it becomes less stable, and less able to support the activity of the crucial respiratory enzyme, cytochrome oxidase. The respiratory activity of the mitochondria declines as the polyunsaturated oils replace palmitic acid, and this change corresponds to the life-long decline of the person's metabolic rate.” - from: “Aspirin, brain, and cancer,” by Dr. Ray Peat
“Compared to the control diet, the high fat diet remodeled liver mitochondrial phospholipid acyl chain composition by 0.6–5.3 fold with notable increases in n-6 and n-3 polyunsaturation. The remodeling in the liver was accompanied by diminished complex I to III respiratory enzyme activity by 3.5 fold. Finally, qRT-PCR analyses demonstrated an upregulation of liver mRNA levels of tafazzin, which contributes to cardiolipin remodeling.”16
“Newly synthesized CL [cardiolipin] contains predominantly saturated fatty acid chains. The primary outcome of CL remodeling is the incorporation of polyunsaturated fatty acids (PUFAs) into CL molecules. Unlike saturated and monounsaturated fatty acids, PUFAs are susceptible to oxidation in the presence of elevated reactive oxygen species (ROS), and oxidation of PUFA-CL has been shown to underlie cellular sensitivity to apoptosis.”17
The main issue with PUFAs is not burning them for energy, as burning PUFAs for energy would not be so bad. However, PUFAs have a long journey from mouth to mitochondria, and many things can go wrong along this journey.
As such, the main concern with PUFAs isn’t even so much whether or not they are oxidized at the time of consumption, as they can cause the same damage even if consumed unoxidized, due to their ability to oxidize in the body, especially once they become incorporated into cells.
“You should eat more PUFAs in the winter, as cold-climate foods are higher in PUFAs.”
There are good reasons why animals and plants in cold climates contain higher levels of PUFAs (reasons that will be discussed in this section), yet these reasons do not make PUFA consumption in winter beneficial as far as optimal health goes.
Here is the thing about Mother Nature - One of the main rules by which she abides is to always prioritize survival at the expense of optimal health. Alive and sick is better than dead, and nature will always make concessions to avoid the latter.
Polyunsaturated oils can be a tool that can help avoid death in cold climates and in times of famine, at the expense of optimal health. They do this in two main ways:
Increasing mobility in cold climates.
Lowering the metabolic rate to spare resources and induce hibernation in a time of limited food (winter).
Increasing mobility is the reason why the fats of fish that live in cold waters or of seeds that mature in late fall are polyunsaturated.
These fats do not harden in cold temperatures, allowing cold-water fish to remain mobile in cold waters (as opposed to hardening like a brick), and allowing the oils in seeds to flow freely to nourish the baby plant that the seed will develop into, without hardening into a solid in the cold soil.
In the case of cold-water fish and Arctic animals, by allowing for better mobility in cold temperatures, these fats provide an evolutionary advantage. As a cold-water fish, if you can’t move, you can’t feed and you won’t be able to survive.
However, here is what’s interesting. Due to the issues that arise because of the structure of these fats (their ability to increase oxidative stress, interfere with metabolic signalling, etc.), even cold-water fish get sicker when fed an excess of fish oil and other polyunsaturated fats.