Here are the claims I see most often, and I provide the truth behind these seed oil myths:
Claim #1: Seed oils are industrial waste products, therefore, unsafe to consume
The claim that a food ingredient is an industrial waste product implies that because it may have been a waste stream at one point in time that somehow makes it bad to consume. Obviously, this reasoning does not prove anything about safety or nutrition of a food ingredient, but also utilizing a waste stream means there’s less waste, which isn’t a bad thing.
The word “industrial” is also used to imply something negative about the ingredient, but many different ingredients we consume are used in other industries (water, salt, baking soda, etc.) and once again, that tells you nothing about the health or safety of that food.
Besides all of that, this claim isn’t even true regarding seed oils. Seed and vegetable oils have been part of human culture for millennia. China and Japan produced soybean oil as early as 3000 B.C. Southern Europeans started to produce olive oil by 2000 B.C. People started producing olive oil in the Middle East almost 8,000 years ago. Canola was bred through conventional plant breeding methods in Canada during the 1960s and ’70s to significantly reduce the levels of erucic acid and glucosinolates in the parent rapeseed for use in food.
Not to mention that the opposite of this claim is actually true. Used seed and vegetable oils are recycled from deep fryers to be used as a direct fuel, as well as in the production of biodiesel, livestock feed, pet food, soap, detergent, cosmetics, and industrial chemicals.
Claim #2: The oils are heated to such high temperatures during refining that it causes them to oxidize
During the refining process, seed oils are heated to a temperature that drives off volatile compounds, which actually makes the oil more stable. This is why refined oils have higher smoke points and a longer shelf life than their unrefined counterparts. That temperature is lower than the temperature that would be necessary to oxidize the oil.
Deodorization is a steam distillation process that drives off the unwanted aldehydes, ketones, alcohols and short chain fatty acids that cause undesirable odors. Careful execution of this process improves the stability and color of the oil, while preserving its nutritional value. After the steam distillation process, the oil is conditioned under nitrogen to prevent oxidation.
Claim #3: Seed oils are washed in solvents like hexane, which is a known neurological toxin
Hexane has been used to extract oils from plant material since the 1930s. After extraction the hexane is then removed from the oil. There is no evidence to substantiate any risk or danger to consumer health when foods containing trace residual concentrations of hexane are ingested.
Refined vegetable oils extracted with hexane contain less than 1 ppm of residual hexane. It’s estimated that the level of ingestion of hexane from all food sources is less than 2 percent of the daily intake from all other sources, primarily gasoline fumes.
Claim #4: Refined seed oils contain significant levels of trans fatty acids
The processes used for deodorization have been modified to limit the production of trans fatty acids. Vegetable, seed and even nut oils, have been found to contain levels of trans-fatty acids that are less than or comparable to the levels in beef fat and cows milk, which contain about 2 to 5 percent of trans-fat as a percent of the total fat.
Claim #5: Seed oils are unhealthy and inflammatory
Evidence strongly shows the opposite of this claim. Human trials consistently show that omega-6 fatty acids do not cause inflammation.
High-quality observational evidence shows modest reductions in coronary heart disease rates by further decreases in saturated fat if replaced by a combination of poly- and mono-unsaturated fat, and the benefits of polyunsaturated fat appear strongest.
Claim #6: The ratio of omega-6 to omega-3 is too high
Both omega-6 and omega-3 polyunsaturated fatty acids are essential and reduce risk of heart disease. The ratio of omega-6 to omega-3 is not useful and can be misleading.
A 2021 prospective analysis showed that replacing butter and margarine with canola oil, corn oil, or olive oil was related to lower total and cardiometabolic mortality. Studies show that a diet high in these fats can help lower cholesterol and blood sugar. An analysis by the American Heart Association found that eating more omega-6 fats either reduced markers of inflammation or left them unchanged. Many studies have shown that rates of heart disease went down as consumption of omega-6 fats went up. The AHA supports an omega-6 PUFA intake of at least 5 percent to 10 percent of energy in the context of other AHA lifestyle and dietary recommendations. They conclude, “To reduce omega-6 PUFA intakes from their current levels would be more likely to increase than to decrease risk for CHD.”
So, as you can see, many of the popular claims surrounding seed oils are not only untrue, but in actuality quite the opposite. Use the oils you prefer, have access to and work best for your application. Spreading disinformation regarding seed oils is yet another classist take, as it demonizes less expensive, more accessible foods.
Food Science Babe is the pseudonym of an agvocate and writer who focuses specifically on the science behind our food. She has a degree in chemical engineering and has worked in the food industry for more than decade, both in the conventional and in the natural/organic sectors.