Is Rapeseed Oil Bad for You? The UK's Most-Used Cooking Oil Examined

Rapeseed oil — sold as canola oil in North America — is the most widely used cooking oil in the UK. It is in the majority of supermarket own-brand vegetable oils, most processed foods, and restaurant fryers. It is often marketed as a healthy choice: low in saturated fat, high in monounsaturated fat, and a source of omega-3.

The reality is more complicated. Rapeseed oil is not as harmful as sunflower or corn oil, but it is not the straightforward health food its marketing suggests.

What Is Rapeseed Oil?

Rapeseed is a bright yellow flowering plant (Brassica napus) grown extensively across the UK — those yellow fields you see in spring are rapeseed crops. The seeds are pressed to extract oil.

The variety sold today as food-grade rapeseed oil is a product of plant breeding: the original rapeseed plant contained high levels of erucic acid (a potentially harmful long-chain fatty acid) and glucosinolates. Modern "low erucic acid rapeseed" (LEAR) was developed in the 1970s to remove these compounds. In Canada, this was branded as "canola" (Canadian oil, low acid).

Fatty Acid Profile

Fatty acid	% in rapeseed oil
Oleic acid (omega-9, monounsaturated)	61%
Linoleic acid (omega-6)	21%
Alpha-linolenic acid (omega-3, ALA)	9–11%
Saturated fat	7%

Compared to sunflower oil (68% linoleic acid), rapeseed oil's 21% linoleic acid looks favourable. The omega-3 ALA content is also often cited as a benefit.

However, there are several important caveats.

Why the Omega-3 Content Is Misleading

The ALA (alpha-linolenic acid) in rapeseed oil is plant-based omega-3 — not EPA or DHA. ALA must be converted in the body to EPA and DHA to be useful for the same biological functions (membrane composition, anti-inflammatory prostaglandin production, brain function).

This conversion is highly inefficient: approximately 5–10% of ALA converts to EPA, and less than 1% converts to DHA. The conversion is also reduced when omega-6 intake is high, because linoleic acid and ALA compete for the same desaturase enzymes.

The practical implication: the omega-3 content of rapeseed oil is largely irrelevant as a health benefit. You would need to consume unrealistic quantities to obtain meaningful EPA/DHA equivalents, and the omega-6 content simultaneously impairs the conversion of any ALA you do consume.

The Processing Problem

The health properties of rapeseed oil depend significantly on how it is produced:

Cold-Pressed Rapeseed Oil

Cold-pressed rapeseed oil is mechanically extracted at temperatures below 60°C without chemical solvents. It retains its natural colour (golden yellow), flavour (mild, nutty), and antioxidants including vitamin E and polyphenols. Cold-pressed rapeseed is a legitimate healthy cooking oil with a reasonable fatty acid profile.

Refined "Vegetable Oil" (Standard Commercial Rapeseed)

The vast majority of rapeseed oil used in UK food manufacturing and sold as "vegetable oil" is refined through a process involving:

1. Seed heating and flaking
2. Hexane solvent extraction
3. Degumming (phosphoric acid treatment)
4. Neutralisation (sodium hydroxide)
5. Bleaching (activated clay)
6. Deodorisation (steam at 200–250°C)

The deodorisation step is particularly concerning. At these temperatures, some of the polyunsaturated fatty acids undergo geometric isomerisation to form trans fatty acids — specifically elaidic acid. Studies have detected small amounts of trans fats in commercially refined rapeseed oil despite the absence of hydrogenation. The quantities are debated and generally below the threshold that triggers mandatory labelling.

The refining process also removes most of the tocopherols (vitamin E) and other protective antioxidants present in cold-pressed oil, reducing the oxidative stability of the final product.

Thermal Stability: A Real Concern

Rapeseed oil's 21% linoleic acid content makes it significantly more thermally stable than sunflower oil (68% linoleic acid) but still considerably less stable than olive oil, avocado oil, coconut oil, or butter for high-heat applications.

When rapeseed oil is heated repeatedly — as occurs in restaurant fryers — the polyunsaturated fraction oxidises to produce aldehydes including 4-hydroxynonenal (4-HNE) and acrolein. A 2015 study in the British Medical Journal found that frying with multiple oils at typical cooking temperatures produced the following aldehyde concentrations:

• Corn oil: highest (well above WHO daily limit)
• Sunflower oil: very high
• Rapeseed oil: moderate (better than sunflower, worse than olive oil)
• Extra virgin olive oil: low
• Coconut oil and butter: lowest

Rapeseed vs. Olive Oil: The Honest Comparison

Rapeseed oil is frequently positioned as a cost-effective UK alternative to olive oil. The comparison:

Property	Rapeseed oil (refined)	Extra virgin olive oil
Linoleic acid (omega-6)	21%	10%
Oleic acid	61%	73%
ALA omega-3	9%	1%
Useful omega-3 (EPA/DHA equiv.)	~0.5–1%	~0.1%
Anti-inflammatory polyphenols	Removed by refining	Yes (oleocanthal, etc.)
Thermal stability	Moderate	Moderate-high
Processing	Heavy chemical processing	Mechanical pressing

For everyday cooking, extra virgin olive oil is superior on every metric that matters — lower omega-6, higher polyphenol content, better-evidenced cardiovascular benefit, and similar thermal stability for home cooking temperatures (not industrial frying).

Filippo Berio Extra Virgin Olive Oil 5L — the cost difference between EVOO and rapeseed oil is approximately £1–2 per week at typical UK usage levels. This is negligible against the difference in fatty acid quality and polyphenol content.

Should You Avoid Rapeseed Oil?

Rapeseed oil is not "bad for you" in the absolute sense. It is substantially better than sunflower or corn oil as a cooking fat. Cold-pressed rapeseed oil is a reasonable option if cost is a significant constraint.

But it is not the health food UK food marketing makes it out to be:

• The omega-3 content does not deliver meaningful EPA/DHA
• Standard refined rapeseed oil has lost most of its antioxidants
• Its linoleic acid content (21%) still contributes meaningfully to omega-6 overload in a diet already high in processed food
• There are clearly superior options at similar price points

For UK consumers looking to reduce their omega-6 load, replacing refined vegetable/rapeseed oil with cold-pressed extra virgin olive oil is the most impactful single change — more important than avoiding any specific processed food.

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