Nutrition myth buster: How worried should you be about cooking with seed oils?

Jennifer Bowden

Nutrition writer·New Zealand Listener·

7 Jul, 2026 06:08 PM4 mins to read

‌

Subscribe to listenAccess to Herald Premium articles require a Premium subscription. Subscribe now to listen.Subscribe now

‌

SaveShare this article

Reminder, this is a Premium article and requires a subscription to read.

Copy LinkEmailFacebookTwitter/XLinkedInReddit

Oils derived from crops such as canola, corn, cottonseed, rice bran, safflower, sunflower and soybeans are frequent targets of claims that they are unnatural and industrial.

As well as Jennifer Bowden’s columns in the NZ Listener, listener.co.nz subscribers can access her fortnightly Myth busters column which explore food and nutrition myths.

The online world is awash with alarming claims about seed oils, including suggestions that they are unnatural and industrial, cause
inflammation and may even be fuelling modern chronic disease. Yet these same seed oils are widely regarded as safe, even beneficial, by nutrition scientists, particularly when compared with alternatives such as butter or lard. So how did one everyday ingredient become so controversial?

Oils derived from crops such as canola, corn, cottonseed, rice bran, safflower, sunflower and soybeans are frequent targets of these claims. Canola oil, in particular, is often portrayed as the product of dubious genetic engineering, linked to industrial rapeseed oil which is used to make lubricants, soap and synthetic rubbers. Because rapeseed oil was not historically used as a food and contains compounds that can be harmful to humans, this association is used to infer that canola oil itself must be suspect.

The reality is less dramatic. Canola oil is indeed derived from rapeseed, but it was developed in the 1970s through selective breeding programmes to remove compounds considered harmful. The oil produced from these modern plants differs substantially in its fat profile from traditional rapeseed oil. While the original rapeseed plant contained compounds such as isocyanates and glucosinolates that may be detrimental to health, these have been bred out of modern canola plants. A similar process can be seen elsewhere in our food supply: modern edible almonds, for example, come from varieties selectively bred to eliminate the bitterness and toxicity found in their wild ancestors.

The claim that these oils promote inflammation is also common online – largely because the omega-6 fatty acids they contain, such as linoleic acid, can be converted in the body into compounds involved in inflammatory processes. From this, it is often assumed that eating more omega-6 fats, through seed oils, must increase inflammation. But the evidence does not support this. In human studies, higher intakes of omega-6 fats, including linoleic acid, did not appear to raise levels of inflammatory markers and in some cases were associated with lower levels.

Broader research points in a similar direction. Recent systematic reviews have found that seed oils can improve blood lipid profiles and help with blood sugar control, suggesting a possible role in managing conditions such as diabetes and cardiovascular disease. Other large-scale analyses have linked higher omega-6 intake with lower risks of heart disease, cancers, and even overall mortality. While these findings are not entirely uniform, the weight of evidence does not support the idea that these oils are uniquely harmful. However, people may report feeling better after avoiding seed oils because the change often coincides with eating fewer highly processed foods overall, rather than any effect of the oil itself.

Still, the intensity of the backlash against seeds oils suggests something more than nutrition science is at play. When people talk about seed oils online, they are not just making scientific claims – they’re also often making value judgments about food. Foods are framed as “good” or “bad”, “clean” or “toxic”, “natural” or “artificial”. In this context, seed oils are rarely described in neutral terms; instead, they are labelled “industrial”, “unnatural” or “dirty”, while alternatives like butter are cast as “clean”, “real” and “ancestral”.

This language echoes earlier trends such as clean eating and reflects a broader pattern of food anxiety in contemporary culture. Seed oils are not simply assessed on the basis of their health effects – they are subject to a moral evaluation. Through this lens, they come to symbolise something larger: concerns about modernity, food processing and a loss of control over what we eat. It is this wider narrative that helps explain why seed oils are so easily cast as harmful, even when the scientific evidence is far more nuanced.

Nutrition science rarely offers simple villains or easy answers. In reality, health outcomes tend to reflect overall dietary patterns rather than any single ingredient – a point often lost in online debates. But the appeal of movements like “seed oil avoidance” lies precisely in that simplicity – a way of restoring certainty, even when the evidence is far more nuanced.

SaveShare this article

Reminder, this is a Premium article and requires a subscription to read.

Copy LinkEmailFacebookTwitter/XLinkedInReddit