Cooking Oils: Which to Avoid and Why
- jadavisr
- Apr 26
- 4 min read
When it comes to healthy eating, the type of fat we consume matters just as much as the quantity. Cooking oils are a kitchen staple, yet many people are unaware that some oils can promote inflammation and contribute to chronic health issues, including heart disease and metabolic syndrome. As a nutritional therapist, I often find clients are surprised by how much difference the right oil choices can make.
In this blog, we will explore which oils to avoid, why they pose risks, and offer healthier alternatives.
Why Are Some Cooking Oils Problematic?
Not all fats are created equal. The cooking oils we choose affect our balance of omega-6 to omega-3 fatty acids, oxidative stress levels, and overall inflammation in the body. Many commonly used oils are high in omega-6 polyunsaturated fatty acids (PUFAs), which, when consumed in excess and in a processed form, can drive inflammation (Simopoulos, 2016).
In addition, cooking oils that are highly processed, refined, and exposed to high temperatures during manufacturing can become oxidised. Oxidised fats have been linked to an increased risk of cardiovascular disease and other chronic conditions (Guasch-Ferré et al., 2015).
Another important factor is how cooking oils are extracted. Cold-pressed oils are mechanically extracted at low temperatures without the use of chemicals or excessive heat. This method helps preserve more nutrients, antioxidants, and natural flavours (Andrikopoulos et al., 2003).
In contrast, refined cooking oils often undergo multiple processing stages, which strip away beneficial compounds and can create harmful oxidation products.
Finally, how you store cooking oils matters. Cooking Oils are highly sensitive to light, heat, and oxygen, all of which accelerate oxidation. Research shows that oils stored in clear plastic bottles exposed to light degrade faster and may develop harmful compounds (Choe & Min, 2006). Oils should always be bought in dark-coloured glass bottles, which protect against light damage. They should be stored in a cool, dark cupboard, away from heat sources like ovens or direct sunlight, and tightly sealed after use to reduce air exposure.
Cooking oil Storage Tips:
Choose dark glass bottles — protects oil quality by blocking light.
Avoid plastic bottles — can leach chemicals and allow faster degradation.
Store away from heat and sunlight — a pantry or cupboard is ideal.
Refrigerate delicate oils like flaxseed or walnut oil to extend shelf life.
Use within 3–6 months after opening for best freshness and health benefits.
Cooking Oils to Avoid
1. Vegetable Oil Blends (e.g., "vegetable oil")
Often labelled simply as “vegetable oil”, these blends typically include soybean, corn, and sunflower oils – all high in omega-6 fats. They are heavily refined, bleached, and deodorised, which strips them of nutrients and promotes oxidation. Excess omega-6 intake, particularly from processed sources, has been associated with inflammatory diseases, obesity, and cardiovascular disease (Calder, 2015).
2. Soybean Oil
Soybean oil is one of the most widely consumed oils but is highly processed and rich in omega-6 fatty acids. Emerging evidence suggests that high intake may negatively impact metabolic health and promote insulin resistance (Deol et al., 2020).
3. Corn Oil
Like soybean oil, corn oil is high in omega-6 fats and often extracted using chemical solvents such as hexane. Studies indicate that overconsumption of corn oil can lead to imbalances in inflammatory pathways (Ramsden et al., 2010).
4. Sunflower Oil (High Linoleic)
While cold-pressed, high-oleic sunflower oil can be a better choice, standard sunflower oil is high in linoleic acid (a type of omega-6 fat). When heated, it can produce harmful compounds, including aldehydes, which are associated with cell damage and chronic disease risk (Gertz, 2014).
5. Rapeseed Oil, Standard, Not Cold-Pressed
Rapeseed oil is often promoted as a healthy option, but much of the commercial supply is refined and deodorised. Although rapeseed oil is lower in saturated fat, the refining process can degrade the quality of the oil, creating oxidation products that may be harmful (Ratnayake, 2000).
What to Use Instead: Healthier Alternatives
Choosing oils that are stable at high temperatures and naturally lower in omega-6 fats is key. Good options include:
Extra Virgin Olive Oil: Rich in monounsaturated fats and antioxidants and associated with reduced cardiovascular risk (Schwingshackl & Hoffmann, 2014).
Avocado Oil: High in monounsaturated fats and stable for cooking at higher temperatures.
Coconut Oil (in moderation): Contains saturated fats that are more stable when heated, although best used occasionally.
Cold-Pressed Rapeseed Oil: A better option compared to standard refined rapeseed oil; high in monounsaturated fats and lower in omega-6 content.
Tip: Even with healthier oils, proper storage and moderate use are key to maintaining their health benefits.
Final Thoughts
The oils we cook with daily can have a profound impact on our health. Reducing intake of highly processed, omega-6-rich oils, opting for cold-pressed and less refined oils, and ensuring oils are stored correctly are simple but powerful steps toward reducing inflammation, improving heart health, and supporting overall wellbeing.
If you are concerned about how your oil choices might be affecting your health or would like personalised advice on diet and chronic disease prevention, feel free to book a no obligation 30 minute chat with me.
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