Seed Oils and Cancer: Separating Myths from Science

Are Seed Oils Really Linked to Cancer? What Science Says

Seed oils have become a controversial topic, with some people blaming them for everything from general inflammation to cancer. But are these oils truly harmful? Or, is this just another case of misinformation?

Let’s break down the science and separate fact from fear.

What Are Seed Oils?

Seed oils are the oil extracted from seeds, including canola, soybean, sunflower, safflower, grapeseed, and corn oil. They are widely used in cooking, processed foods, and health supplements like evening primrose and borage oil. These oils are rich in polyunsaturated fats, particularly omega-6 fatty acids, which are essential fatty acids, crucial to our body's optimal functioning.

But how much is too much?

The Seed Oil and Cancer Debate

Recently, headlines have suggested that seed oils may be driving colon cancer in young adults. This claim was fueled by a study published in Gut, which examined the lipid (fat) content in colorectal cancer tumors. However, the study did not actually conclude that seed oils cause cancer. Instead, it found that tumors contained higher levels of certain inflammatory lipids, particularly those derived from arachidonic acid, an omega-6 fatty acid.

Here’s the problem: media outlets and influencers extrapolated the findings and made broad claims about seed oils being the cause of cancer in young adults. But the study itself never made that claim. In fact, here is what one of the researchers wanted people to know from their work:

“It is well known that patients with unhealthy diets have increased inflammation in their bodies ... We now see this inflammation in the colon tumors themselves, and cancer is like a chronic wound that won’t heal – if your body is living off of daily ultra-processed foods, its ability to heal that wound decreases due to the inflammation and suppression of the immune system that ultimately allows the cancer to grow.” 

The wake-up call was more general about the Western diet and how it allows, or even promotes, the growth of colorectal cancers. The PR release went on, "According to Yeatman [one of the researchers], this study emphasizes the urgent need to reevaluate the components of the Western diet, which typically consists of excessive consumption of added sugars, saturated fats, ultra-processed foods, chemicals and inflammatory seed oils."

Was the Seed Oil Headline Just a Distraction?

The researchers themselves have previously found a similar detrimental effect of inflammation from Western diets with heart disease. Remember, data on the harms of a diet of ultra-processed foods (aka Western Diets or Standard American Diets) is strong enough to be considered factual now. There is no debate that Western diets increase systemic inflammation and the risk of heart disease, cancer, and dementia. The researchers believe it is "added sugars, saturated fats, ultra-processed foods, chemicals and inflammatory seed oils" that are to blame.

Our attention should be on the totality of a Western diet, and in some ways, the seed oil headlines have distracted us from looking at Western diets in general.

Are Omega-6 Fats Really Bad for You?

While it would be convenient for everything to be good or bad, once again, we need to understand this in context.

Omega-6 fatty acids are one of two essential fatty acids for humans, meaning our bodies require them but we can’t produce them on their own. The key is balance. A high omega-6 to omega-3 ratio in the diet can promote inflammation, which may contribute to the inflammation underlying chronic diseases, including cancer. However, omega-6 fats are not inherently harmful—it’s the excessive consumption, especially from ultra-processed foods, that is problematic.

Chemicals (like hexane) in the Seed Oils? 

It is true that chemically processed oils can contain residues of the very chemicals used to extract the oil from the plant or seed. Ingesting chemicals like hexane is never a good idea. This highly toxic chemical's "safe" levels are debatable, so we advise zero as the ideal amount of intake. While there is no conclusive evidence that hexane causes cancer, there is also no evidence showing that hexane doesn't cause cancer! The question has simply not been studied enough to know the answer. That said, hexane is clearly toxic to nerves (a neurotoxin), and we can't imagine it's doing any actual good, so it's best to avoid it. That means it is best to opt for cold-pressed oils whenever possible, which is a mechanical pressing of the oils out of the plant/seed.

Ultra-Processed Foods: The Bigger Concern?

Many foods high in seed oils are also ultra-processed, meaning they contain additives, preservatives, and low amounts of fiber and antioxidants. Studies have linked ultra-processed food consumption to increased risks of obesity, diabetes, heart disease, and cancer. This suggests that the real issue may not be seed oils themselves, but the fact that they are regularly used in ultra-processed food.  

How to Make Healthier Choices

Here are some ways to maintain a healthy balance:

1. Increase Omega-3s—Eat more fatty fish (salmon, sardines, herring, mackerel, anchovies), walnuts, chia seeds, and flaxseeds, or consider taking a fish oil or algae-based omega-3 supplement.

2. Choose Cold-Pressed Oils—Opt for minimally processed oils like cold-pressed olive oil, avocado oil, or expeller-pressed seed oils.

3. Eliminate Ultra-Processed Foods— Focus on whole, nutrient-rich foods instead of processed snacks, fried foods, and fast food. Make ultra-processed foods the exception, not the rule in your diet.

4. Check Your Cooking Oils—Instead of using chemically refined vegetable oils, try cooking with extra virgin olive oil, coconut oil, or butter (if your dietary preferences allow it).

The Bottom Line

There is no strong scientific evidence that seed oils directly cause cancer. The real issue lies in the overconsumption of ultra-processed foods, which often contain highly refined versions of seed oils, added sugars, and artificial ingredients. Instead of demonizing seed oils, a more balanced approach is to avoid highly processed foods, focus on whole foods, consume a variety of healthy fats, and an overall anti-inflammatory diet high in a wide variety of vegetables.

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