Are seed oils actually bad for you?

Few nutrition topics generate more heated debate right now than seed oils. On one side, influencers and podcasters are declaring them toxic and responsible for the obesity epidemic, cancer, and chronic disease. On the other, mainstream nutrition bodies continue to recommend them as heart-healthy alternatives to saturated fat. The truth, as is almost always the case in nutrition science, sits somewhere more nuanced than either camp acknowledges.

Here is an honest, evidence-based assessment of what we actually know.

What are seed oils?

Seed oils are oils extracted from the seeds of plants. The ones most commonly discussed include sunflower oil, vegetable oil, rapeseed oil, safflower oil, corn oil, soybean oil, and cottonseed oil. They are widely used in food manufacturing and home cooking, and they are a primary ingredient in the vast majority of ultra-processed foods.

They are distinct from other plant oils like extra virgin olive oil, avocado oil, and coconut oil, which are extracted from the fruit rather than the seed and processed very differently.

The omega-6 argument

The primary concern raised about seed oils is their high content of omega-6 polyunsaturated fatty acids, particularly linoleic acid. The argument goes like this: linoleic acid converts in the body to arachidonic acid, which is a precursor to pro-inflammatory compounds. Therefore, high seed oil consumption drives inflammation.

This is a biologically plausible mechanism. The problem is that the clinical evidence for it is less clear than the social media debate suggests. A systematic review of 15 clinical trials found no consistent evidence that increased omega-6 intake raises inflammatory markers. However - and this is an important caveat - those studies had significant limitations including small sample sizes, short durations, and the use of biomarkers that may not capture subtle inflammatory shifts.

So the honest position is: the inflammation argument is not definitively proven, but it is also not definitively disproven. The mechanism is plausible and the research is insufficient to close the question.

The processing problem

What is less contested is the processing issue. Seed oils are extracted through industrial processes involving high heat, chemical solvents, bleaching, and deodorising. By the time the oil reaches your kitchen or a food manufacturer's facility, most of the naturally occurring nutrients, antioxidants, and phytochemicals present in the original seed have been removed.

This is meaningfully different from cold-pressed or minimally processed oils like extra virgin olive oil, where the polyphenols and antioxidants that give the oil its health properties are preserved.

Highly refined seed oils are essentially stripped of nutritional value before they are used. That alone is a reason to prefer less processed alternatives, independent of the inflammation debate.

The omega-3 to omega-6 ratio

What we do know with reasonable confidence is that the ratio of omega-3 to omega-6 in the modern diet is significantly skewed towards omega-6. Current estimates suggest most people in Western countries consume an omega-6 to omega-3 ratio of around 15:1 or higher, compared to the estimated evolutionary ratio of closer to 4:1.

This matters because omega-3 and omega-6 fatty acids compete for the same enzymes in the body. When omega-6 is present in excess relative to omega-3, the balance of signalling molecules produced shifts in a more pro-inflammatory direction. The solution is not necessarily to eliminate omega-6 - we need it, and in the right amounts it is beneficial - but to dramatically increase omega-3 intake and reduce excessive omega-6 consumption.

The primary sources of omega-3 are oily fish (salmon, mackerel, sardines, anchovies), walnuts, flaxseed, and chia seeds. Most people in the UK are significantly deficient in omega-3, and a high-quality fish oil supplement is one of the most evidence-based nutritional interventions available for reducing inflammation, supporting cardiovascular health, and protecting brain function.

Why this is particularly relevant for women in perimenopause and menopause

Chronic low-grade inflammation is directly relevant to the hormonal transition of perimenopause and menopause. Inflammation worsens insulin resistance, disrupts the HPO axis that governs hormone production, impairs gut health and oestrogen clearance, and contributes to the joint pain, fatigue, brain fog, and mood changes that many women experience during this stage.

The dietary pattern that drives chronic inflammation - high in ultra-processed foods, refined seed oils, sugar, and low in oily fish, vegetables, and fibre - is also the pattern most likely to worsen perimenopausal symptoms. An anti-inflammatory dietary approach is therefore not just a general wellness recommendation for this group. It is a clinically relevant intervention.

What actually matters most

The seed oil debate is a distraction from the more important point, which is this: the problem is not seed oils in isolation. The problem is ultra-processed food, of which seed oils are an ingredient.

Ultra-processed foods - which include not just obvious junk food but cereals, breads, crackers, plant-based milks, sauces, protein bars, and many other everyday items - are the primary vehicle through which most people consume excessive seed oils. They are also low in the nutrients, fibre, and phytochemicals the body needs, and high in additives, preservatives, and refined carbohydrates that drive inflammation independently of the oils they contain.

The most practical response to the seed oil debate is therefore not to spend time agonising over which oil to cook with, but to reduce ultra-processed food consumption overall, increase whole food intake, and prioritise omega-3 from oily fish and good quality supplementation where dietary intake is insufficient.

When cooking at home, choosing extra virgin olive oil, avocado oil, or butter for high-heat cooking is a sensible default. Not because seed oils are definitively toxic, but because these alternatives are less processed, more nutritionally intact, and better evidenced for health benefits.

The bottom line

Seed oils are not the poison they are often portrayed as on social media. But they are also not neutral. Highly refined, stripped of nutritional value, consumed in excess through ultra-processed food, and contributing to an imbalanced omega-3 to omega-6 ratio - there are good reasons to minimise them in favour of less processed alternatives.

The bigger picture is the dietary pattern, not a single ingredient. And for most people, particularly women navigating the inflammatory dimension of perimenopause and menopause, shifting towards a whole food, anti-inflammatory dietary pattern will produce far more benefit than obsessing over any one ingredient.

If you would like to understand how your current diet is affecting your hormonal health and inflammation levels, I offer personalised nutritional therapy consultations tailored to exactly this kind of assessment.

Book a free 20-minute consultation to find out how I can help, or explore my Women's Health Nutrition Packages and General Nutrition Packages.