Seed Oils: Friend or Foe?

Seed oils have sparked debate in recent years, with some claiming they are harmful while others argue they are beneficial in moderation. Let's break down their health effects and how they compare to other oils.

Are they healthy?

Some of the controversy surrounding seed oils centres on their omega-6 content. While essential, excessive intake (without balancing with omega-3s) may contribute to inflammation. However, recent research suggests that plant-based oils, including seed oils, are associated with a lower risk of cardiovascular disease when consumed in moderation[3].

The real concern arises when these oils are repeatedly heated at high temperatures, which can strip nutrients and form harmful compounds[4][5]. However, this issue is more relevant in industrial settings like restaurants with infrequent oil changes, rather than in typical home cooking where you’re cooking at lower temperatures.

Most seed oils are processed via hexane extraction - normal in food processing. While some evidence suggests hexane could be linked to several health conditions[6], after being extracted, the oil is then bleached and deodorised to remove colour, additives and potentially harmful compounds. For those wary of chemical processing, cold-pressed oils—produced without heat or solvents—offer an alternative, albeit at a higher cost.

Additionally, seed oils are commonly found in ultra-processed foods (UPFs), which are linked to inflammation and other health risks[7]. However, it’s important to consider these negative health effects may actually reflect the effects UPFs, where these oils are commonly used. Since UPFs also contain added sugars, refined starches, and additives—each associated with inflammation—it’s difficult to isolate the impact of seed oils from the broader dietary context.

Are some seed oils better than others?

No matter the processing method, a seed oil’s health value depends on its final nutrient composition at the point of purchase.

Consider the nutrition label and fatty acid composition for these rapeseed oils taken from a specific product (A), and from the UK’s authoritative nutrition database, McCance and Widdowson's The Composition of Foods (B):

Looking at the nutritional contents and fatty acid composition of this oil:

• Low amount of saturated fatty acids per 100ml
• Of the monounsaturated fatty acid (MUFA) content, ~61-71% is the omega-9 oleic acid that makes extra-virgin olive oil so famous for its heart-healthy properties
• Of the polyunsaturated fatty acid (PUFA) content, 21-23% is omega-6 linoleic acid and ~11% is omega-3 alpha-linolenic acid (the highest ALA content of any vegetable oil)
• What you don't see on this label: the presence of plant sterols, vitamin E, and vitamin K1

This is a nutritional powerhouse, boasting several cholesterol-lowering and cardio-protective properties, such as the polyunsaturated-to-saturated fatty acid ratio, plant sterols, and the antioxidant vitamin E. However, due to misinformation about their supposed dangers on social media, people are now avoiding these seed oils.

In comparison to sunflower oil, rapeseed oil offers a healthier fat profile, with more omega-3s, lower omega-6s, higher monounsaturated fats, and lower saturated fat. Its omega-6 to omega-3 ratio of around 2:1 supports better dietary balance, while sunflower oil’s omega-6 dominance (with a much higher ratio) may promote inflammation if not offset by omega-3-rich foods.

Are seed oils truly as harmful as claimed?

Seed oils aren’t inherently harmful—their impact depends on how they’re consumed. Moderation and balancing omega-6 with omega-3 are key, with an optimal ratio of around 4:1 omega 6 – omega 3.[8]

Opting for cold-pressed or minimally processed versions can be a healthier choice because they retain more nutrients and natural compounds due to their extraction process.[9] Olive and avocado oils offer added benefits due to their high MUFA and antioxidant content, supporting heart health through their anti-inflammatory properties. Meanwhile, seed oils provide vitamin E and unsaturated fats.

For best overall health, focus on a diverse intake of fats, including olive oil, nuts, seeds, and oily fish for omega-3s. Prioritising your overall dietary pattern —rich in vegetables, whole grains, lean proteins, and healthy fats—is more beneficial than fixating on individual ingredients.

Written by Abigail Attenborough

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