If you have any interest in health and nutrition you've probably come across talk about seed oils being bad for you. It's not a new discussion, but it's certainly become more prominent in recent years. Is it unwarranted fear mongering or is there research supporting the claims of these oils being toxic?
Generally when people refer to "seed oils" they are talking about products that are usually labelled as "vegetable oil". Of course these aren't actually oils from vegetables. It's believed this label came into being because one of the first oils of this type to be marketed for human consumption was cottonseed oil, which was better known as lamp oil at the time and would probably be seen as something we shouldn't be eating. When people refer to seed oils they're usually taking about corn, cottonseed, canola, soybean, sunflower, safflower, rice bran and grapeseed oils. These are usually all highly processed oils.
There seem to be three main camps against seed oils; the majority say that it's just the 8 above mentioned highly processed and refined oils that are the problem and virgin, cold pressed oils are fine. Another camp says that all oils coming from plants are toxic while another camp says it's just the oils very high in Omega-6 fatty acids that are problematic.
Are Seed Oils Beneficial in Any Way?
A lot of the claims that seed oils are bad for us don't seem to be being made out of the blue. When you look into it a good amount of evidence is being cited. So recently I've been trying to find out what the evidence to the contrary is from those who advocate for vegetable oils as being beneficial for us. Frustratingly, most of the time these advocates don't really tell us anything other than that studies have found them to be beneficial, leaving me wondering in what way. When really pressed on how they are beneficial, the only answer they seem to have is that they have been shown to reduce cholesterol, which doesn't necessarily demonstrate a benefit, especially with questions being raised as to whether cholesterol is actually as bad as we've been led to believe it was all these years.
These are just a handful of articles which discuss the lack of evidence in studies of saturated fat consumption causing heart disease and how dietary recommendations should be or are starting to be changed:
https://pmc.ncbi.nlm.nih.gov/articles/PMC9794145/
https://pubmed.ncbi.nlm.nih.gov/31841151/
https://bjsm.bmj.com/content/51/15/1111
https://www.jacc.org/doi/10.1016/j.jacc.2020.05.077
Interestingly, during my research into why seed oils are thought to be toxic for us I came across a mention of a study that found that carb consumption with saturated fats increased insulin resistance at a higher rate than carbs consumed with seed oils. So could this be seen as a benefit, despite the fact that insulin resistance still increased with seed oils, just not as rapidly as with saturated fats?
How might consuming seed oils be harmful?
Back to the argument on the side of seed oils being toxic; if we look at the argument that it's the extraction and refining process that is the biggest issue, why could that be a problem?
When an oil is extracted through traditional methods from seeds or fruits with high oil content the product is just pressed to force the oils out. The resulting oil is called virgin oil and is unadulterated with all the nutrients and vitamins it carries still intact. It will also have the flavour of the fruit or seed it comes from. However, if a seed doesn't contain much oil or if they want to extract more oil from the already pressed oils or fruits, then they have to employ high heat, higher pressures and add a solvent. This produces a sludgy looking oil which then has to be refined and cleaned to make it look nicer and to remove the solvent. This process removes the flavour and most of the nutrients and vitamins, which is why they might add vitamins back in.
Concerns with this form of processing is that traces of solvent might remain in the oil, the high heat and pressure could be causing higher peroxidation rates which aren't detectable through smell or taste like they would be with cold pressed oils. A question also arises as to whether some of the removed nutrients could help mitigate the damage from peroxidation products in our bodies?
So what is peroxidation?
Polyunsaturated fatty acids start to become unstable over time. This process occurs quicker once they've been released from their wholefood state. Heating increases that peroxidation process and with the high pressure, high heat and often chemical processing, further peroxidation occurs. It seems that it's the peroxidation end products that can cause harm in the body rather than the original oils themselves.
Most plant oils are high in Linolaic Acid (LA) which is an Omega-6 polyunsaturated fatty acid. Along with Omega-3 it's classed as an essential fatty acid because our bodies cannot produce it but it essential for certain body functions. However, if we have more than our body needs then it gets put in our fat stores which means it's hanging around in our bodies for longer. Does this mean it will continue to peroxidate in our bodies? Some believe so.
The Omega-6/Omega-3 imbalance issues
Then there is the belief that the issue is more to do with the imbalance in our bodies between Omega-6 and Omega-3 when we consume too much seed oil. The main function of Omega-6 is to cause inflammation when we get sick or injured in order to summon the immune system to that area for repairs. Omega-3 is the counter balance which stops the inflammation from spreading where it's not needed and brings down inflammation once healing is done. Both fatty acids use the same enzyme pathways for conversion for their respective uses and when Omega-6 levels are too high they will crowd Omega-3 out. For a long time many felt the solution to this was to up Omega-3 intake in order to try and balance the ratios out, but this is actually quite hard to do because most foods with Omega-3 also have Omega-6 in at the recommended or higher 6 ratios. Only some seafoods and fish have higher Omega-3 to 6 ratios. So more recently it's being recommended that the best way to balance out your Omega-3 to 6 ratios is by cutting out high Omega-6 foods, namely seed oils.
From testing done on people eating ancestral diets (that is original diets from their region without any outside influences) it seems they always got enough of both of the Omega fats from the natural foods they were eating, leading to the hypothesis that it is our consumption of the processed oils with high Omega-6 which is leading to our bad balance of these fats. As these populations eating the ancestral diets were also free of the chronic diseases that have become so common today, it could also indicate that it might be that we only require low levels of these fats for optimal health, which might be why some have come to the conclusion that any plant oil is too much unsaturated oil.
Concluding thoughts
I'm not inclined to believe that all plant oils are bad. After all, olive oil has been used for millennia in Mediterranean diets and is only recently we've seen a rise in chronic diseases. Admittedly olive oil is a mono-unsaturated fat rather than polyunsaturated, which means that it's a bit more stable and less prone to peroxidation. Cold pressed polyunsaturated oils haven't ever really been used to the same degree as olive oil has been, so we can't really say what their effects would be if they were used at these rates.
It's actually very hard to do proper scientific studies on the effects of diet, so we can never be truly sure if or how what we're eating is affecting us. Some studies done in the past have revealed a certain amount, but they cannot ethically be repeated today. I keep coming across mention of a heart health study which replaced saturated fats with polyunsaturated ones in the form of seed oils and they found that cancer rates increased with those consuming the seed oils. Unfortunately I don't have access to those studies myself, so I can't corroborate that. I do, however, believe that we've spent thousands, if not millions, of years eating whole, minimally processed foods and it's not a stretch to conclude that our bodies would struggle to adapt to eating something so highly processed and removed from its original form in just over 100 years.
Do you think the growing distrust of vegetable oils is justified?
I'll leave with this video for some more food for thought.
