Fertility Nutrition – Women's Health, Pregnancy & Early Life

Are Seed Oils Toxic to our Health & Fertility?

The most misunderstood nutrition topic

Gettyimages 2162243089 Seed Oil Web

Are Seed Oils Toxic? Separating Myth from Science

You’ve probably seen headlines or social media posts claiming that seed oils are toxic, “pro-inflammatory,” or harmful to fertility and long-term health. With so much conflicting information online, it’s easy to feel confused.
So, what does the science actually say about seed oils, inflammation, and heart health?

Where the “Seed Oils Are Bad” Myth Comes From

Much of the fear around seed oils stems from concerns about omega-6 polyunsaturated fatty acids (PUFAs), which are found in oils like soybean, sunflower, safflower, and corn oil. Some claim that omega-6s drive inflammation and increase disease risk.

A widely cited study used to support this claim is the Sydney Heart Study (1968–1973). In this trial, men who had experienced a cardiovascular event were encouraged to increase their omega-6 intake via margarine. The results showed worse heart outcomes, which led some to blame omega-6 PUFAs.

But here’s the catch: the margarine used at the time contained high levels of trans fats due to hydrogenation. Trans fats are now well-established as harmful to heart health. This makes the study heavily confounded — and it’s not fair to blame omega-6 oils for those outcomes.

What the Totality of Evidence Shows

When we look at modern, high-quality studies, the picture is very different:

  • Omega-6 PUFAs lower LDL cholesterol, a major risk factor for cardiovascular disease. (Farvid et al., 2014)
  • Diets rich in omega-6s are associated with a reduced risk of heart disease and all-cause mortality. (Ramsden et al., 2013)
  • Replacing saturated fats with polyunsaturated fats can reduce cardiovascular events by up to 32%. (Mozaffarian et al., 2010)

The main caveat is that a very small proportion of people with specific genetic variants may be more sensitive to high omega-6 intake (we’ll return to this shortly). For the overwhelming majority, omega-6 PUFAs are safe and beneficial.

Do Omega-6s Increase Inflammation?

Contrary to popular claims, omega-6 fats do not increase inflammatory markers in humans. Large reviews and meta-analyses show no evidence that omega-6 PUFAs cause chronic inflammation. (Johnson & Fritsche, 2012)

Does the Omega-6 to Omega-3 Ratio Matter?

You may have heard that the balance between omega-6 and omega-3 is what matters most. But current evidence suggests that the absolute intake of omega-3s is far more important than the ratio itself.
What this means: eating less omega-6 won’t improve health outcomes — but eating enough omega-3s will.
Plant-based omega-3 (ALA) is found in flaxseed oil, chia seeds, hemp seeds, and walnuts. Marine sources like oily fish and algae provide EPA and DHA, which are even more potent for heart, brain, and fertility health.

Is Everyone the Same? What About Genetic Variants?

This article is based on the scientific evidence available at the date of publication — which consistently supports the benefits of omega-6s. Still, not everyone processes fats the same way. Variants in the FADS1 and FADS2 genes affect the body’s ability to convert shorter-chain omega-6 (linoleic acid) and omega-3 (ALA) into their longer-chain, biologically active forms. Some people carry “low-activity” versions of these genes, which reduce conversion efficiency. (Glaser et al., 2010)

In some population studies, these variants have been linked to less favourable metabolic markers (higher fasting insulin, triglycerides, or insulin resistance) when diets are high in omega-6 but low in omega-3. (Blomquist et al., 2025)

What this means in practice:

  • For most people, omega-6s are protective and beneficial.

For those with these variants (which can’t be easily known without genetic testing), it’s especially important to:

  • Prioritise omega-3 intake (EPA, DHA, ALA).
  • Choose high-quality oils (cold-pressed, minimally processed).
  • Limit ultra-processed foods, which often combine seed oils with sugar, refined carbs, and additives.

This is a good example of precision nutrition — tailoring advice to individual biology, which is an emerging science.

Understanding Different Types of Fat

To put seed oils in context, it helps to understand the three main types of fat:

  • Saturated fats – solid at room temperature (butter, lard, coconut oil). High intakes raise LDL cholesterol and increase cardiovascular risk.
  • Monounsaturated fats (MUFA) – liquid at room temperature (olive oil, avocado, nuts). These are heart-healthy and anti-inflammatory.
  • Polyunsaturated fats (PUFA) – liquid at room temperature (seed oils, walnuts, fatty fish). Includes omega-6 and omega-3 fatty acids, both of which are essential for health.
  • Both MUFA and PUFA are strongly beneficial for heart, metabolic, and fertility health.

Seed Oils, Fertility, and Women’s Health

So what about fertility? Are seed oils toxic for reproductive health?
The answer is no. There is no scientific evidence that seed oils harm fertility. In fact, omega-6 and omega-3 fatty acids are essential building blocks for cell membranes and hormone production, both of which are critical for reproductive health. (Chavarro et al., 2007)

However, quality matters:

  • Cold-pressed oils retain more natural compounds like vitamin E and plant phytonutrients, which provide antioxidant benefits beyond the fat profile itself.
  • Extra Virgin Olive Oil (EVOO) is considered the gold standard — rich in MUFAs, polyphenols, and antioxidants, with strong evidence for benefits in cardiovascular, metabolic, and fertility health. (Martinez-Gonzalez et al., 2019)

The Problem Isn’t the Oils — It’s the foods they’re in.

It’s worth noting that around 60% of seed oil intake comes from ultra-processed foods — like packaged snacks, baked goods, and fast food. These foods don’t just contain seed oils — they’re also high in added sugars, refined starches, sodium, preservatives, and additives, all of which are strongly linked to poor health outcomes. (Monteiro et al., 2019). So, the real issue is not the oils themselves, but the dietary context in which we consume them.

Takeaway

  • Seed oils are not toxic.
  • Omega-6s lower LDL cholesterol and reduce cardiovascular risk.
  • The omega-6:omega-3 ratio is less important than ensuring adequate omega-3 intake.
  • Cold-pressed oils provide extra nutrients (vitamin E, phytonutrients).
  • EVOO remains one of the best oils for overall and fertility health.
  • The main risk comes from ultra-processed foods, not the oils themselves.
  • A very small subset of people with genetic variants may need to be especially mindful of balancing omega-3 with omega-6.

Bottom line: Don’t fear seed oils. Instead, focus on whole foods, quality oils, and getting enough omega-3s for optimal health and fertility.

 

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