Many people ask me about seed oils, and it seems 2024 was the year where they came into the spotlight.

You may have heard mutterings that cooking oils that come from seeds are bad for our health, with some concerns that they cause inflammation and are even “toxic” for the body.

So what’s the deal with them? Which oils are the ones currently being demonised?

Common examples include:

You’ll often find them added to ultra-processed foods, as well as in bottles sold in the supermarkets. In fact, most vegetable oils are seed oils.

Understanding how we consume seed oils in our diet is really important (used in a small amount in cooking or as an additive to ultraprocessed foods), as a lot of associations quoted from research in media and social media seem to skip over this really important point.

Many people accuse the omega-6 content of seed oils as the reason for why they are unhealthful. Omega-6 is a type of fatty acid needed from the diet that is linked to good skin and cellular health. Seed oils contain a specific type of omega-6 fatty acid called “linoleic acid”. Linoleic acid is converted to arachidonic acid, and it is the arachidonic acid that is rumoured to be bad for us as it is linked to generating compounds which play a role in regulating inflammation.

This is where the bad rep comes from! Especially when there are so many health conditions that can link back to high levels of inflammation – cancer, heart disease, mental health issues to name but a few.

However, when you look at the research picture to date, that is not what the science seems to suggest.

Inflammation: One systematic review from 2011, demonstrated that high intakes of linoleic did not seem to increase levels of arachidonic acid in the body. In fact, from what we understand, only a very small percentage of linoleic acid gets converted to arachidonic acid and the researchers explained that there were cases in some studies where participants consuming the highest amounts of linoleic acid actually had the lowest levels of inflammation.

Heart Disease: Researchers from a review in 2020 found that higher levels of linoleic acid was linked to a reduction in cardiovascular (heart) disease. Whilst, another study finding similar results – that linoleic acid intake and arachidonic acid levels didn’t raise the risk of heart disease, and those with higher amounts in the bloodstream were 7% less likely to develop it.

Bowel cancer: Recently, there has been much attention in the press over the impact of cooking oils as a risk factor for bowel cancer. This media speculation comes from the recent publication of a US study, looked at 81 tumour samples in people aged between 30 to 85 and found that they had higher levels of bioactive lipids attributed to seed oils.

While our food choices have an impact on every cell in the body, these findings cannot be suggested as being direct i.e. not directly connecting the fats (lipids) found in the tumours to seed oils in the diet. It is important to acknowledge that this research was carried out in a relatively small sample over in the US (different countries have different diets and food standards). It may well be that this study provides the springboard for further research and discoveries, but there are too many confounding factors to suggest that seed oils cause bowel cancer from this one paper alone. Researchers commenting on the studies findings have also have pointed to the potential effects of the seed oils within ultraprocessed foods specifically vs seed oils alone.

Does arachadonic acid do any good? Arachidonic acid in it’s own right is important for wound healing and blood clotting in times when the body is under stress and injury.

So what’s the bottom line? To eat or not to eat?

Like everything to do with nutrition, we all have unique relationships with food, so if you want to avoid seed oils, then you are of course free to do so. However, if the reason for cutting them out/ being overly concerned about the health impacts/ inflammation then you can rest easy that and in fact, from the evidence we have to date, they may bring more healthful qualities than compared to other fats like butter, lard, ghee.

The main issue with seed oils is that they are mostly found in highly processed and highly calorific foods and take aways. Reducing the intake of ultra-processed food, whether made with seed oils or not, would have more health benefits than simply cutting down on seed oil used in cooking. A lot of these foods are high in refined sugar, fat and salt, which do more damage to our health than from what we can understand seed oils can do on their own.