​How to think about cooking oils

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When choosing cooking oils, the two most important factors are:

• how the oil is extracted and processed

• how stable the oil is when exposed to heat, air, and light

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In practical terms, focus on:

• whether the oil is cold-pressed or heavily refined

• how easily it breaks down when heated

• whether chemical solvents were used during processing

• whether the oil is pure or a blend

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Cooking oils that are minimally processed and more stable hold up better. Oils that are heavily processed and unstable break down more easily.

 

Where exposure comes from

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With cooking oils, exposure mainly comes from processing methods and breakdown during heat.

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Many refined seed oils are extracted using high heat and chemical solvents such as hexane. While some of this is removed during processing, trace residues can remain. The bigger issue is what happens when these oils are heated.

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Oils that are high in polyunsaturated fats (common in seed oils) are more prone to oxidation. When they break down, they can form harmful compounds such as:

• aldehydes

• lipid peroxides

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These compounds can form during both industrial processing and everyday cooking, especially at higher temperatures.

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Over time, repeated intake of oxidized oils and these breakdown products is associated with inflammation, cellular stress, and metabolic strain.

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Blended oils add another layer. When oils are mixed, it often reduces transparency and can combine multiple lower-quality sources, making it harder to know how stable or processed the oil actually is.

 

What to look for when buying cooking oils

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You don’t need to overcomplicate it — a few clear guidelines go a long way.

• Choose cold-pressed oils when possible
  These avoid chemical solvents like hexane and stay closer to their natural state

• Use more stable oils for cooking
  Oils like olive oil, avocado oil, and coconut oil are less prone to breaking down under heat

• Limit refined seed oils
  Oils like canola, sunflower, safflower, soybean, and corn oil are more prone to oxidation and breakdown

• Be cautious with blends
  Mixed or “vegetable oil” blends are often the least transparent and lowest quality

• Pay attention to packaging
  Dark glass bottles are better than clear plastic, which can expose oils to light and leaching

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These simple shifts can significantly reduce exposure to degraded and highly processed oils.

 

Common labels explained

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Cold-pressed / Expeller-pressed
Oil extracted mechanically without chemical solvents. Generally less processed.

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Refined
Oil that has been filtered, heated, and processed to remove impurities. Often more stable than raw seed oils but more processed.

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Vegetable oil / Oil blends
Usually a mix of different refined seed oils. Quality and composition can vary widely and are often not clearly disclosed.

 

Bottom Line

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Cooking oils differ most in how they are processed and how stable they are when used. Cold-pressed oils that are more stable tend to break down less and avoid chemical solvent exposure. Refined seed oils and blends are more heavily processed, more prone to oxidation, and more likely to form harmful compounds like aldehydes and lipid peroxides.

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The goal is to choose cooking oils that are minimally processed, more stable under heat, and lower in overall toxic byproducts.