(Learning Curve) Are Seed Oils Harmful?
If you’ve spend more than 40 seconds on social media, you’ve probably seen people warning everyone about the dangers of seed oils. And because the seed oil thing is one of the more complicated and confusing arguments for laypeople to interpret, it’s easy to just take peoples’ word for it.
So to prevent you from doing that, I’m going to step in here and break it all down for you.
Also: I’m really sick of hearing about how poisonous these oils are, from people who have zero clues.
I guess I’m revealing where I stand on the matter, but that shouldn’t be the end of the story. I have my opinions, but I’m not entitled to my own science. None of us are, which is why when you see someone giving an opinion on something, you should ask them for the science they’re using to back their statements up. You’ll be surprised to see that a lot of people won’t have anything to show you, or that what they do show you is poorly done and doesn’t prove their point.
Welcome to the post-truth era, I guess.
I’m going to get right into the claims that are made about seed oils, and what the latest science says about them.
Note that I don’t work for any seed oil-related industries, so don’t email me or comment telling me I’m a shill.
What are seed oils?
The term ‘seed oils’ is often used interchangeably by diet warriors to refer to both oils that come from seeds – like canola and safflower, and vegetable oils, such as corn and soybean.
These oils are generally extracted from the plant using a chemical solvent, then they’re deodorized and refined in order to neutralize odours and taste. Sometimes, companies will extract oil by crushing the seeds from plants instead of using chemicals. These products are often labelled as ‘cold-pressed’ or something similar.
But does extraction method really make a difference in the healthfulness (or not) of these oils?
Although all oils are a combination of monounsaturated, polyunsaturated, and saturated fatty acids (no, olive oil isn’t pure monounsaturated fat), seed and vegetable oils tend to have high levels of polyunsaturated fats, otherwise known as PUFAs.
These PUFAs have been vilified by ‘doctors’ like Mark Hyman, LCHF/Keto diet warriors, and jerks like the Food Babe, who say the inflammation PUFAs cause is responsible for everything from chronic disease like cancer, Alzheimers, heart disease, and obesity. These people also claim that PUFA oils contain toxic chemicals and GMOs that should never be consumed.
Sounds scary. But is this true?
PUFAs can be categorized as omega-3s and omega-6s. There are some others, but they’re irrelevant to this post.
You might know of omega-3s as the ‘healthy fats,’ and you may have heard of omega-6s as being the ‘harmful, inflammatory fats.’
So all oils have some level of PUFAs, which can further be categorized as omega-3, 6, or 9.
This chart from Nutrition Action shows the fatty acid content of popular fats:
So many questions! Let’s get after them.
Seed Oils and Inflammation.
I want to start here, because in years past, even I got caught up in the claim that seed oils cause inflammation. I’m sure there’s an old blog post or something hanging around that has me talking about how omega-6s are inflammatory. But because I’ve since had many conversations about it with scientists like Kevin Klatt and the Food Science Babe among others, and had to do research on it for my cooking oil post as well as my upcoming book, Good Food, Bad Diet, I’ve changed my tune. It’s safe to say that I’ve been around the block with the existing research about PUFAs and inflammation.
And by ‘existing research,’ I mean recent, well-done studies with solid methodology. Not studies exclusively done in rodents or in lab dishes because, well, are you a rat?
To start, I agree with claims that our intake of PUFAs has increased dramatically with our consumption of ultra-processed foods. Rarely are these foods made with high-monounsaturated fats; you’ll usually find polyunsaturated fats in these foods, in combination with added sugars and refined grains.
Perhaps not a coincidence, prevalence of some chronic diseases in North America has also risen during this time.
But what do PUFAs have to do with this?
Believers in this claim hypothesize that chronic disease risk increases with chronic inflammation in the body, which I’m not here to argue about (because it’s probably true).
The question here is, are PUFAs responsible for the inflammation that’s causing these diseases?
There’s SO MUCH conflicting information about this, I almost drove myself nuts parsing it all out. Thankfully, I had help from people who do science even more than I do.
Here’s the deal:
Although the cells involved in inflammation have high levels of arachidonic acid (a PUFA) in them, a link between PUFAs and inflammation has never been proven.
A 2019 review of studies in Circulation found that high levels of linoleic acid – a PUFA – were associated with reduced risk of cardiovascular events.
And while there are several papers by James DiNicolantino in particular that appear to connect PUFAs with adverse health outcomes, it is widely known that this guy is a pharmacist who calls himself ‘doctor,’ promotes sauna for covid treatment and to ‘eliminate toxins,’ and is a huge anti-PUFA low carb advocate. He can’t back up any of his claims with proper research, though. His references for this commonly cited paper, for example, include studies done as far back as 1965, and many others done on mice.
No thanks. I’ll get my research from someone who doesn’t spout conspiracy theories or get their information from old Cosmo articles.
A 2017 review of studies found no connection between a diet high in PUFAs and inflammatory markers. This 2020 review of studies drops the mic on the inflammation hypothesis as well as the importance of the omega-3:omega-6 ratio:
“The reason that the omega-6 to omega-3 PUFA ratio seems unimportant in predicting cardiometabolic disease or inflammation is probably because concerns about this ratio are partly formed on the basis of a number of incorrect and simplified assumptions—for example, that omega-6 PUFAs overall are proinflammatory, that omega-6 PUFAs (and linoleic acid in particular) have adverse effects on cardiovascular disease risk (although in fact omega-6 and omega-3 PUFAs are related to lower risk), and that reducing linoleic acid intake will lower arachidonic acid concentrations (by contrast, linoleic acid supplements do not increase arachidonic acid concentrations in plasma or adipose tissue).”
That being said, preliminary research suggests that any differences in how we respond to PUFAs may lie in our genes…because of course it does.
As far as PUFAs causing disease, nobody has ever isolated these fats as a cause of any disease or condition. But it’s not a far reach to assume that people who eat large amounts of refined oils, probably eat large amounts of them in ultra-processed food. That their diet quality may not be very high, with few fruits and vegetables, and less fiber than recommended.
Seed oils and cooking.
When we cook with oils, we subject them to heat. Grapeseed, canola, and sunflower oil, all three of which are considered PUFA ‘seed oils,’ have the highest smoke points of all the commonly-used cooking oils. They also contain at least two double bonds in their structure, which makes them more volatile under heat. When oil is heated beyond its smoke point, these bonds begin to break down and react with oxygen, forming polar compounds which may be harmful to our health.
But that’s only part of the story.
How often do you fry?
How long is your oil at this temperature?
How high are you heating your oil?
I can tell you this: don’t heat your oils beyond the smoke point, and if you use high-heat cooking, don’t do it for hours (which you’re probably not…I mean, how long does it take to make french fries?)
If you’re deep frying with vegetable oil, you should be tossing it afterwards instead of reusing it. Polar compounds accumulate over time with high heat cooking.
They’re GMO, and that’s bad.
When are we going to stop demonizing GMOs? There is NO credible research showing that GMOs are harmful to human health. Period.
Seeds oils are laden with chemicals from the refining process.
The ‘chemical’ scare tactic is a favorite of people in the wellness industry, and yes – there are chemicals such as hexane used in the oil refining process. But even so, the finished product has minute amounts of those chemicals. When I say ‘minute,’ I mean, for example, canola oil has 0.8 parts per million per kilogram of oil.
If you’re still worried about the refining process, you can always buy cold-pressed canola oil. It’s expensive, but it does exist.
Seed oils contain trans fats.
This one is true, actually!
The oil refining process causes trans fats to form, although they are present in very, very low levels in the refined oils we cook with. Any amount of trans fat isn’t good, and they do add up, if you’re eating one type of oil multiple times a day. Vary the types of fats you consume, and you shouldn’t have an issue.
They’re modern, and since our paleo ancestors didn’t eat them, we shouldn’t either.
I’ll bet the people who believe this stuff take antibiotics, eat seedless watermelon and orange carrots, and use lightbulbs.
Those things didn’t exist in the paleo era either, but hey, science.
Instead instead of nitpicking over fats, it’s so much more productive and smart to concentrate on the overall quality of your diet. Nobody eats these oils in isolation, so it’s time to replace the hysteria about seed oils with a greater understanding of the importance of our total dietary patterns.
Beware of blanket statements about foods like, ‘X contains toxic chemicals’ or ‘Y is inflammatory, never eat it!’
There really isn’t any food on the planet that we should NEVER eat. And while fear sells books and diets and products, it’s counterproductive and unnecessary, especially around food and eating.