Seed oils are the new sugar, which was the new gluten, which was the new animal protein, which was the new carbs, which was the new saturated fat.
It’s the latest nutritional boogeyman being blamed for the ongoing public health catastrophe that is our diabesity epidemic.
The anti-seed oil influencers are everywhere, and they’re becoming mainstream. Here’s a few of the prominent influencers that have made an impact on popular culture:
Dr. Cate Shanahan is the author of Deep Nutrition and nutritionist for the Lakers. She made news early in the pandemic when she was on Bill Maher’s show talking about poor metabolic health caused by seed oil consumption leading to preventable Covid deaths
Mark Sisson is the author of MarksDailyApple, a prominent website in the paleo diet movement. He’s also the founder of Primal Kitchen, a company that was started by marketing avocado oil mayonnaise, created with the premise that seed oils are bad for you. Primal Kitchen was sold to Kraft-Heinz for $200 million, suggesting the market here is actually pretty big.
Dr. Paul Saladino is author of the Carnivore Code and has 1.7 million Instagram followers. You may have seen one of the viral videos where he goes to well known chain restaurants and pesters their staff about ingredients in their food.
If you haven’t heard of seed oils, a quick Google search brings up articles suggesting concern about the health impact of seed oils from outlets as diverse as Harvard, the Food Network, and Rolling Stone.
You may even come across something about the Bitcoin Carnivores, who think of seed oils as “fiat food” the way they think of the US dollar as “fiat currency.”
I think seed oils is such an interesting topic partly because of the increasing attention it’s getting, and partly because it illustrates scientific illiteracy really well.
The way that topics like this are discussed are a huge reason why people often find nutrition to be so complicated.
So let’s dive right in.
What are seed oils?
Seed oil is a general term that refers to the oil produced from a number of different commodity crops.
The most common oils that are in the seed oil group are things like canola oil, soybean oil, corn oil, cottonseed oil, sunflower oil, safflower oil.
Those are ingredients that are probably in many of your pantries. You’ve probably cooked with one of them recently and I’m sure that you’ve eaten many things containing them over the last few days.
One of those is in almost every single shelf stable food product AKA processed food.
There are a bunch of different ways to slice and dice it up, and it quickly gets confusing.
Cate Shanahan refers to the majority of seed oils we consume by the moniker “Hateful 8,” but that’s an incomplete list, and it’s not worth diving into the rabbit hole to think about the difference between high oleic versus non-high oleic varieties.
Why might seed oils be bad?
The case against seed oils boils down to 3 major arguments:
The biological plausibility of harm
The high omega 6 to omega 3 ratio that we consume with significant seed oil consumption may push some biological systems towards more inflammatory pathway. I wrote about this in more detail in prior post on fish oil.
Seed oils are mostly polyunsaturated fatty acids, which can become oxidized easily. Oxidized fatty acids may contribute to heart disease. Seed oils also don’t have natural antioxidants the same way that other oils like olive oil do.
Processing methods of seed oils may lead to trans fat formation. Trans fats are bad, and that’s something almost everything in nutrition agrees on.
The changes across the population over time mirror changes in disease incidence
People consume more seed oils than ever before and we have more obesity and diabetes than ever before:
The Lindy effect, precautionary principle, naturalistic fallacy, or something else about it being unnatural (kind of a corollary to point 1).
Seed oils are new to human consumption and we haven’t adjusted to be able to consume much linoleic acid (the predominant omega 6 in many seed oils) without it leading to bad biologic effects
Seed oils may sound really bad, but the arguments are only persuasive if you cherry pick evidence
Unfortunately, the arguments against seed oils don’t really pass muster if you look at actual studies in humans that look at endpoints that we care about.
The evidence against seed oils boils down to a sleight of hand that people advocating for almost every fad diet perpetuate.
Step 1: show a mechanistic connection between the problem and bad outcomes
You can see this with almost every single study cited by the anti-seed oil folks. Take a look here:
It’s a lot of PubMed IDs to cite.
But look at what the content is actually saying.
It doesn’t prove that seed oils cause heart disease. It just says that seed oils raise some blood markers in the short term. All the other PubMed IDs mentioned are similar.
We get no information about risk of actual heart disease. We just get short term info about a biomarker.
It’s a quality of evidence I would never accept to decide about whether to prescribe a drug or send someone for a procedure.
Step 2: show that there’s an connection in the epidemiology - the more we eat, the sicker we get
I pasted that graphic from Shanahan’s website above. But you’ll see graphics like that in a number of other sources:
You could plot out a lot of different things on that graphic and it would look the same - just because things are rising together doesn’t mean one causes the other.
Step 3: animal studies further reinforce the hypothesis
There’s an adage in pediatrics that “kids aren’t little adults.” It means that diseases and treatments in kids aren’t the same as they are for adults - you need to think differently.
The nutritional corollary to that is that mice aren’t little humans.
Every single time I see an animal model cited as proof that some dietary component is bad, I feel sad about the state of our global scientific literacy.
It doesn’t tell me anything useful to hear about cancer being cured in a mouse.
And it’s equally uninformative to hear about the impact of seed oils, animal protein, or some other bad guy in the way that a mouse develops chronic disease.
The arguments against seed oils aren’t different than the arguments for a plant based diet
They’re equally weak and rely on sleight of hand to make the case.
A bit of mechanistic evidence from one paper, coupled with an epidemiologic connection from another, add in an animal study.*
The seed oil people do the same thing that the gluten people or the carnivore people or the plant based diet people all do to advocate for their preferred way of eating: cherry pick the data and tell an incomplete story.
You can read the China Study or watch Game Changers and come away with the conclusion that a vegan diet is the way forward for health.
Hearing the story of a famous person employing that method makes it feel even more persuasive.
But it’s all a shoddy way to interpret evidence.
Nutrition research is hard to do, and most of it misinforms more than it helps you understand anything.
The real trials in humans that look at the outcomes that we care about don’t show that seed oils are harmful.**
So what explains all of this data if it’s wrong? Or why my cousin who cut out seed oils feels so amazing?
Correlation doesn’t equal causation.
Those graphs showing a rise in chronic disease at the same time we have a rise in seed oil consumption seem really persuasive until you think about the confounders.
Where do you find seed oils in 2023?
The answer is that they are in every single processed food. Almost every cheap and shelf stable source of highly palatable calories has seed oils in it.
In other words, is it really the corn oil that’s making you sick, or is it the Doritos? Are you sure the canola oil is the problem and it’s not the Oreos?
And along with that increase in seed oil consumption comes an overall increase in calories.
How can you have any confidence that it’s the soybean oil rather than the total calorie consumption?
I have zero certainty that these associations are going to play out when they’re studied well.
The data are too confounded to make heads or tails of it all.
Is it possible that seed oils really are bad for you?
Absolutely.
But it’s equally likely that seed oils are just a proxy for more calories, less activity, and a Western lifestyle.
Cutting out seed oils probably makes people feel better because they eat less junk and ultimately fewer calories.
There may be something to the hypothesis that seed oils cause disease. But for now, that’s all it is: a hypothesis, and one that’s lacking a solid base of evidence.
*If you’re wondering why I’m not discussing the Minnesota Coronary Experiment and the Sydney Diet Heart Study, it’s because my interpretation of those studies is that the conflict between the initial analysis and a re-analysis requires another trial to replicate the findings before I’m persuaded.
**I would strongly recommend this video from Layne Norton breaking down the flaws with this research if you’re looking for more here: