Seed oils aren't demonstrably bad for you... so why don't I cook with them?
- Michael Blackburn
- Aug 10
- 4 min read
This is a topic that generates a lot of emotion, and there are a lot of people who won't even read past the opening line to see what informs my opinion. I initially bought in to the "seed oils are bad" side of the argument but I try to remain flexible and sometimes, when the evidence simply doesn't support the argument, you have to be willing to adjust your stance. Let's take a look at both sides and see what see what the science says.
Let's start with what exactly seed oils are: seed oils are vegetable oils extracted from the seeds of plants, specifically soy, canola (rapeseed), sunflower, corn, grapeseed, flax, etc. They are rich in polyunsaturated fatty acids (PUFAs) and Omega 6s and are commonly used due to their affordability, shelf life and heat tolerance.
So, what are some of the things that fall on the negative side? In high amounts they are pro-inflammatory with the associated risks: cancer, cardiovascular disease and metabolic syndrome. Observational data in populations with lower (but not zero) seed oil consumption show a lower incidence of these risks. When seed oils (most oils, actually. Studies have found a similar process occurs in ghee, olive oil, etc.) are heated to high temps they oxidize and produce harmful byproducts (aldehydes, etc.). Reheating amplifies those effects: oxidation worsens, trans fats and lipid peroxides form, all of which can pose significant health risks. Studies have shown links between frequent consumption of fried foods and cardiovascular disease. In most cases, seed oils undergo industrial processing using additives. This can result in traces of hexane remaining in the finished product. High temp processing can partially hydrogenate the oil, creating trans fats. It also strips oils of natural anti oxidants like vitamin E, leaving them more prone to oxidation. Lastly, they displace healthier fats in the diet (monounsaturated and Omega 3s) and they have high energy density, potentially contributing to obesity and metabolic issues when over consumed.
That's quite a list. So, what arguments can be made on the positive side? To begin with, meta analyses of controlled studies by independent groups indicate that Omega 6s do not increase markers of inflammation when balanced by adequate Omega 3 consumption. To put that in perspective, the ideal consumption ratio of Omega 6s to Omega 3s is 2:1 or 3:1. Modern diets have shifted that ratio to 10 and even 20:1. This leads to a pro-inflammatory imbalance as excess Omega 6 consumption inhibits the conversion of Omega 3 into anti-inflammatory compounds. Therefore, problems likely arise more from broader lifestyle and dietary choices than seed oil consumption alone. Harmful effects require excessive, unbalance consumption. Chronic disease in populations that consume high amounts of seed oils is more than likely driven by over consumption of ultra processed and/or fried foods combined with a sedentary lifestyle. Regarding the negative effects of oxidation, it occurs mostly at high temps and prolonged repeated heating. Seed oils used in moderate heat cooking or raw applications minimize these risks. For example, high quality canola oil has been shown in clinical trials to improve HDL/LDL profile and ranks with olive oil in that respect. And high quality and canola oil are not mutually exclusive terms. You can buy top quality organic, expeller pressed canola oil. It costs about the same as any other top quality oil and eliminates one of the key factors driving the commercial use of seed oils, the fact that they're cheap. Lastly, modern processing methods mean that most seed oils contain little to no trans fats, and hexane residue is tightly regulated and present in such small amounts that it is unlikely to impact health.
So, what are our key takeaways here? Multiple independent studies (i.e. not funded by seed oil industry groups) have shown that canola oil used to replace other dietary fats (butter, coconut oil, lard...) leads to better blood indicators for heart health, inflammation, etc. One of these studies was even funded by a pro coconut group. Instead of avoiding Omega 6s entirely, people should look to decrease their overall intake of them and increase their intake of Omega 3s to restore proper balance. We should also prioritize whole, minimally processed foods and avoid heavily processed (highly palatable, cheap, convenient, high in carbs and fats, lead to caloric excess and weight gain) foods and fried foods. Lastly, MOVE! All of these things coupled with low levels of physical activity/sedentary lifestyles are more than likely the root, or close to it, of most of our problems.
Given all of this, why do I choose not to cook with seed oils for my clients? It all comes down to that healthy ratio. I have no idea how they eat outside of the meals I provide them and therefore have no idea idea how much seed oil they are consuming. I choose not to increase their intake above what they already consume. Their is one instance where I do cook with seed oils. Occasionally a client family will request chicken nuggets for the kids. In this case I use canola oil because to use a non seed oil would be prohibitive. I use a thermometer to carefully monitor the temp and only use the oil one time and then discard it.
Here are some links to people who do a great job on explaining all of this, including two who do a great job actually reviewing the meta analyses of a number of seed oil studies, and played a great part in helping me make an informed decision:
Marc Morris:
Mike Israetel:
Dr. Gil Carvalho:
DR. Michael Ruscio:
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