Refined Vegetable Oils: Health Risks and Glycidol

What Are Refined Oils and How Are They Produced?

To understand the associated health risks, we first need to clarify what refined oils actually are and how they are manufactured through industrial thermal processing.

What are refined oils?

Refined oils are plant-based oils that undergo a multi-stage industrial process of chemical treatment and purification. Unlike cold-pressed oils, which are gently extracted at a maximum of 40 degrees Celsius without the use of chemical additives, refined oils undergo intensive chemical processing and high thermal processing. The primary aim of refining is to render the oil neutral in flavour, extend its shelf life, and raise its smoke point – making it ideal for food manufacturers and high-temperature frying. However, this process comes at a heavy cost: the formation of toxic compounds.

How are refined oils manufactured?

The industrial refining of vegetable oils takes place across several stages, each requiring specific chemical agents and thermal processing:

• Degumming: Removal of phospholipids and proteins using acids or alkalis
• Neutralisation: Treatment with alkaline solutions to remove free fatty acids
• Bleaching: Use of bleaching clays to decolourise the oil and filter out lipid oxidation products
• Deodorisation: Heating to 180–270°C to strip away volatile odours and unpalatable flavours

The final stage – industrial deodorisation at extremely high temperatures – is particularly problematic: this is where hazardous contaminants like glycidol (glycidol fatty acid esters) and 3-MCPD are generated. These substances are unavoidable by-products of industrial refining present in virtually every refined oil.

Refined vegetable oils list: which oils are commonly refined?

Almost all standard cooking oils are commercially available in refined form. The most common refined vegetable oils list includes:

• Sunflower oil (refined)
• Rapeseed oil (refined)
• Soya oil (refined)
• Palm oil
• Corn oil / maize germ oil
• Groundnut oil / peanut oil (refined)
• Sesame oil (refined)

You can identify refined oils because the packaging will not state “cold-pressed”, “extra virgin”, or “virgin”. If the label simply reads “vegetable oil” or “cooking oil”, it is almost certainly a refined product. Claims such as “ideal for frying” or “high smoke point” also typically indicate an oil rich in polyunsaturated fatty acids that has undergone high-heat refining.

The Dangerous Contaminants in Refined Vegetable Oils

During the refining process, two particularly harmful chemical compounds are generated that pose significant risks to human health.

What are glycidol and 3-MCPD?

Glycidol is a genotoxic carcinogen that directly induces DNA damage. Unlike many other contaminants, there is no safe intake threshold for glycidol – even minute amounts can theoretically initiate carcinogenic mutations. Both the World Health Organization (WHO) and the European Food Safety Authority (EFSA) classify glycidol as a substance of critical concern.

3-MCPD (3-monochloropropane-1,2-diol) is likewise a carcinogen, though non-genotoxic. This means there is theoretically a threshold dose below which 3-MCPD is considered harmless. The tolerable daily intake (TDI) is established at 2 micrograms per kilogram of body weight. Nevertheless, 3-MCPD remains a problematic toxicant capable of damaging the kidneys and reproductive organs.

Both substances form during industrial deodorisation at temperatures exceeding 200°C and are unavoidably present in refined vegetable oils. By their own admission, manufacturers have yet to develop a process that eliminates these contaminants entirely without compromising the commercial “quality” and stability of the refined oil.

Why is vegetable oil bad for you?

Refined oils present major health concerns for several distinct reasons:

1. Genotoxic contaminants: Glycidol directly damages cellular DNA and can cause mutations that trigger cancer.
2. Loss of essential micronutrients: Chemical processing and thermal refining strip away naturally occurring vitamins, minerals, and protective antioxidants.
3. High cumulative exposure: Because refined oils are ubiquitous across ultra-processed foods (ready meals, baked goods, crisps, and takeaway foods), daily exposure is immense.
4. Accelerated toxic compound formation upon heating: When polyunsaturated oils are reheated or used for deep-frying, lipid oxidation accelerates, generating further toxic breakdown products.

The danger lies not merely in occasional consumption, but in chronic, daily exposure sustained over decades.

What is the ALARA principle in food safety?

Because glycidol is a genotoxic carcinogen with no safe exposure threshold, food safety authorities apply the ALARA principle: “As Low As Reasonably Achievable”.

This principle dictates that unavoidable food contaminants must be reduced to the lowest feasible level. It applies to substances that cannot be eliminated completely from the food chain but are proven to harm human health. For consumers, the ALARA principle provides a clear recommendation: avoid refined oils wherever possible and choose unrefined, cold-pressed oils instead.

Interestingly, the ALARA principle is also the standard protocol in radiology to minimise radiation exposure during medical imaging – demonstrating how seriously health authorities regard the hazards of genotoxic substances.

Cancer Risk from Refined Vegetable Oils: What Do the Studies Say?

The scientific literature regarding glycidol and the broader health risks of refined oils is deeply concerning.

Are refined oils carcinogenic?

Yes, refined oils contain glycidol, an established genotoxic carcinogen. Being genotoxic means it directly alters the genetic material within our cells. Such DNA damage can lead to uncontrolled cell division – the fundamental trigger of cancer.

In animal bioassays, glycidol induced multiple forms of tumours in rats and mice, including tumours of the mammary glands, thyroid, testes, and brain. Using these toxicological datasets, researchers calculated the corresponding cancer risks for humans.

How dangerous is glycidol in cooking oils?

The figures are startling: an acceptable cancer risk benchmark is conventionally set at 1 in 100,000 – meaning a maximum of one additional cancer case per 100,000 individuals is considered tolerable. For glycidol, in a person weighing 70 kilograms, this equates to less than 1 microgram per day.

However, the real-world data reveals a very different picture:

• Average glycidol exposure in the general population: over 50 micrograms daily
• This is more than 50 times the acceptable benchmark
• For children, exposure reaches up to 200 times above the acceptable risk limit

A Swedish study by Aasa et al. (2019) evaluated internal glycidol doses in children and concluded that their estimated cancer risk is dramatically elevated. The authors called for urgent regulatory measures to reduce glycidol levels across the food supply.

What makes this especially concerning is that glycidol does not accumulate in body fat; instead, it reacts rapidly with cellular DNA. Consequently, each separate exposure can cause irreversible damage, creating a cumulative lifetime risk.

Are refined oils dangerous for children?

Yes, children are particularly vulnerable for several key physiological and dietary reasons:

1. Higher relative dietary intake: Children consume significantly more food and energy relative to their body weight than adults.
2. Infant formula: Commercial baby formulas rely on refined oils containing substantial levels of glycidol fatty acid esters.
3. Longer latency period: Carcinogenesis can take decades to develop – exposure in early childhood provides the longest timeframe for cellular damage to manifest as clinical disease.
4. Rapidly dividing cells: Growing children experience high rates of cell division – precisely the phase when genotoxic DNA damage causes the most catastrophic harm.

As early as 2009, the German Federal Institute for Risk Assessment (BfR) concluded that infants fed exclusively on commercial baby formula ingest concerning quantities of glycidol. Comparable levels of glycidol have similarly been recorded in infant formulas across the United States and Europe.

The guidance from healthcare authorities is clear: breastfeeding is the best option for infants, not least because breast milk contains no detectable levels of glycidol or 3-MCPD.

A further significant finding emerged from a large-scale epidemiological study of over 100,000 women: frequent consumption of fried foods – which are predominantly prepared in refined vegetable oils – was associated with a significantly reduced life expectancy. In men, regular consumption of fried food was linked to a 35% higher risk of prostate cancer. Accordingly, medical experts recommend that individuals at elevated risk of prostate cancer drastically reduce their intake of deep-fried food as a sensible precaution.

Refined Vegetable Oils vs Cold-Pressed Oils: The Crucial Difference

Not all oils are created equal. When evaluating cooking fats, the manufacturing method and thermal processing make the decisive difference to your health.

Is refined vegetable oil healthy? The difference between refined and cold-pressed

The distinction lies in the extraction process and the resulting nutritional and health properties:

Cold-pressed oils are extracted mechanically from seeds, nuts or fruit without the application of high heat or chemical agents. As a result, they retain their natural flavour, rich colour and, above all, their delicate micronutrients. Labelling such as “cold-pressed”, “virgin” or “extra virgin” denotes cold-pressed oils.

The higher smoke point of refined vegetable oils is their only purported “advantage” – yet this comes at a substantial cost to your health. For higher-temperature cooking, naturally heat-stable virgin alternatives like coconut oil or avocado oil can be used instead, tolerating heat without developing toxic compounds.

Why refined oil is bad: Do refined oils contain trans fats?

This is a common point of confusion: no, refined oils do not typically contain trans fats – at least not in notable amounts. Trans fats are formed primarily during the hydrogenation of fats (chemical hardening), a separate industrial process used in products such as hard margarines.

However, that does not mean refined vegetable oils are safe – quite the contrary: contaminants such as glycidol fatty acid esters and 3-MCPD are arguably more hazardous than trans fats, as they cause direct DNA damage. Whilst trans fats primarily elevate cardiovascular disease risk, glycidol acts as a potent genotoxic carcinogen.

Whenever oils are subjected to high heat – whether refined or unrefined – trace amounts of trans fats can nevertheless develop, particularly during repeated frying cycles and the lipid oxidation of vulnerable polyunsaturated fatty acids. This represents another compelling reason to avoid deep-fried takeaway foods.

Practical Recommendations: Alternatives to Refined Oils

The good news: there are safe, unadulterated and wholesome alternatives to refined oils.

Refined vegetable oils list of alternatives: What should you use instead?

Here are the best culinary alternatives that you can use with complete confidence:

For cold dishes (salads, dressings):

• Extra virgin olive oil – rich in polyphenols and antioxidants
• Cold-pressed flaxseed oil (linseed oil) – exceptional omega-3 content
• Cold-pressed hemp seed oil – optimal fatty acid balance
• Cold-pressed walnut oil – rich in alpha-linolenic acid

For medium-temperature cooking and sautéing:

• Virgin olive oil (up to 180°C)
• Virgin coconut oil (up to 177°C) – thermally stable and resilient
• Butter or ghee (clarified butter, up to 200°C)

For high-temperature frying and roasting:

• Avocado oil (virgin, up to 260°C) – exceptionally high smoke point
• High-oleic sunflower oil (cold-pressed, up to 210°C)
• Coconut frying oil (up to 234°C)

Alternative cooking methods requiring no oil:

• Air fryer – crisp textures with minimal or no added fat
• Steaming – gentle method that preserves delicate micronutrients
• Braising in vegetable stock – flavoursome and wholesome
• Oven baking on greaseproof paper – perfect for homemade chips and roast vegetables
• Grilling – achieves rich flavour without added oil

When shopping, keep the following in mind:

• Look for descriptions such as “cold-pressed”, “virgin”, “extra virgin”, or “unrefined”
• Choose oils in dark glass bottles to prevent light-induced lipid oxidation
• Store your oils in a cool, dark cupboard
• Avoid products labelled simply as “refined” or generic “vegetable oil” (understanding why is vegetable oil bad for you begins with this industrial deodorisation process)
• Cut down on supermarket ultra-processed foods, commercial pastries and ready-fried convenience snacks

The most important recommendation: reduce your overall reliance on extracted fats and prioritise whole, unprocessed foods. Whole nuts, seeds and avocados supply beneficial fats in their natural food matrix – entirely free from harmful chemical contaminants.

Conclusion: Why Refined Vegetable Oils Are Best Avoided

The scientific evidence is unambiguous: refined vegetable oils contain glycidol fatty acid esters, a genotoxic carcinogen that causes direct DNA damage. With an estimated average daily intake exceeding 50 micrograms – over 50 times the acceptable safety threshold – overall dietary exposure remains alarmingly high. Children face the greatest vulnerability, with glycidol intake reaching up to 200 times the acceptable cancer risk benchmark.

To date, the manufacturing sector has not established a method to carry out industrial deodorisation and refining without generating these processing contaminants. For consumers, the ALARA principle – “as low as reasonably achievable” – means in practice: avoid refined vegetable oils wherever possible.

The reassuring takeaway is that superior options are readily available. Cold-pressed oils and unrefined native fats supply essential nutrients without contaminant burdens. Furthermore, modern cooking techniques such as steaming, grilling, or using an air fryer make deep-frying entirely obsolete.

Protect your health and your family’s wellbeing: replace refined vegetable oils with wholesome, unrefined alternatives and cut back on commercial fried foods. Your cellular health will thank you.

Scientific Sources

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• Bakhiya N, Abraham K, Gürtler R, Appel KE, Lampen A. Toxicological assessment of 3-chloropropane-1,2-diol and glycidol fatty acid esters in food. Mol Nutr Food Res. 2011;55(4):509-21.
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• Federal Institute for Risk Assessment (BfR). Initial evaluation of the assessment of levels of glycidol fatty acid esters detected in refined vegetable fats. BfR Opinion No. 007/2009, 10 March 2009.
• Larsen JC. ILSI Europe Report Series: 3-MCPD esters in food products. Summary report of a workshop held in February 2009 in Brussels, Belgium. ILSI Europe. October 2009.