Could consuming seed oils give you colon cancer?

The study has reignited claims that seed oils are toxic and that we are being “unknowingly poisoned” by them. But are these oils really to blame for the increase in cancer rates?

Unanswered questions

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“This study highlights the role of diet, as Western diets rich in omega-6 fatty acids like arachidonic acid may exacerbate the inflammatory environment that drives colorectal cancer,” says Dr Zeyad Nassar, a postdoctoral research scientist at the South Australian Health and Medical Research Institute.

Although both omega-6 and omega-3 fatty acids come from our diet, the study did not look at patient dietary histories. That means, Nassar says, the connection between diet and colorectal cancer was hypothesised.

And because the samples came from patients already diagnosed with colorectal cancer, they might have lipid dysregulation, says Dr Joachim Worthington, an epidemiologist at The Daffodil Centre, a joint venture between the Cancer Council and the University of Sydney. “Their body might not be able to metabolise those lipids for any number of reasons,” Worthington says.

Mahon agrees: “It’s the chicken and the egg. Did it really come from diet or could it be something inherently to do with the cancer that’s made those patterns the way they are?”

Still, experts agree it’s a solid launchpad for future research to explore mechanisms that link poor diet to cancer.

So where does that leave us with seed oils?

The key takeaways

Omega-6s are a type of polyunsaturated fatty acid (PUFA), which help to stimulate skin and hair growth, maintain bone health, regulate metabolism and maintain the reproductive system.

Concerns about seed oils typically arise from the way they are processed: the use of extreme heat and chemical solvents, such as hexane, to extract the oil; deodorisation and refining processes that reduce healthy antioxidants.

Research suggests residual hexane from processing falls below harmful thresholds – we are likely to be exposed to more hexane from breathing in fuel fumes from cars on the road. But when consumed in excess, seed oils may contribute to inflammation.

Our consumption of these oils has tripled in the past few decades, primarily because they are used in fast foods and UPFs. Our intake of these foods has continued to rise, while our intake of minimally processed foods has declined over time.

Not only are people often consuming them in excess, but when these oils are reheated repeatedly, as is the case in some fast food outlets, unhealthy trans fats can form in the oils.

Instead of avoiding seed oils completely, there’s good evidence that increasing our intake of omega-3 fatty acids – found in fatty fish such as salmon, tuna, mackerel and sardines as well as walnuts, flaxseeds and chia – is beneficial.

Dr Evangeline Mantzioris, program director of nutrition and food sciences at the University of South Australia, did her PhD examining the effect of tinkering with omegas on rheumatoid arthritis.

“Omega-3 fatty acids have been shown to be beneficial in reducing inflammation as you are increasing the omega-3 levels in your cells,” Mantzioris says. “More of those anti-inflammatory mediators can then dampen down the inflammatory response for rheumatoid arthritis.”

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At present, there are “well-established” dietary factors that can increase or decrease the risk of cancer, says Dr Lisa Mielke, head of the Mucosal Immunity and Cancer Laboratory at the Olivia Newton-John Cancer Research Institute.

Alcohol consumption, smoking, excess weight and consumption of processed meats increase the risk, while having a mostly plant-based, minimally processed and diverse diet decreases the risk – seed oils or no seed oils.

“There’s no one food that will be magical in your diet to transform your health,” Mantzioris says. “It’s about the whole dietary pattern.”

For cancer information and support call the Cancer Council’s 13 11 20 Information and Support line.

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