Calorie and fat content aren’t what make certain oils unhealthy. What does is the source, extraction method, and processing method used.
Even the healthiest starting products (like olives) can make unhealthy oils based on how it was extracted and processed (for eg. light olive oil or olive pomace oil, which are both refined).
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During processing, refined oils – like canola, corn, soy, sunflower, safflower, cottonseed, peanut, and vegetable oils – are heated to high temperatures and heavily processed, which causes the unsaturated fatty acids from the seeds to oxidize, creating byproducts that are harmful to human health, including trans-fats which spark inflammation, age us, and contribute to chronic illness and heart disease.
For example, research at the University of Florida at Gainesville found trans-fat levels as high as 4.6 percent in commercially available canola oil. (1)
Refined oils are extracted with a chemical solvent, typically hexane, which is a petroleum by-product that is classified as a neurotoxin by the US CDC.
Refined oils are bleached, deodorized (because rancid oil smells bad), and steam-cleaned before they make it into the bottle.
On the other hand, unrefined oils are expeller pressed. They’re put through a machine that presses the oil out of a nut or seed through high pressure. The friction of the machine creates heat, which can damage some more sensitive oils.
Cold pressed oils are those that are expeller pressed, under controlled cool temperatures to prevent oxidation or damage of delicate oils. For example, extra virgin / first cold pressed olive oil. These are my top 3 picks for unrefined oils.
Tips from my book: The Real Food Grocery Guide