What to Know About Seed Oils
By Lizzie Streit, MS, RDN, LD
Seed oils have been a hot topic for the past several years, but they’ve recently gained even more attention. Everyone from influencers and podcasters to politicians and fast food chains are talking about them, even going so far as to highlight one chain’s switch from vegetable oil to beef tallow for frying foods on national television.
Amidst all the buzz about seed oils, it’s easy to miss the discussions on the science behind the topic. In this article, you’ll learn what defines a seed oil, how they’re made, and any pros and cons of consuming them.
What are seed oils?
Seed oils refer to a group of cooking oils made from the seeds of certain plants and include canola, corn, cottonseed, grapeseed, rice bran, safflower, soybean, and sunflower oils.
Although there are other seed oils like flaxseed and sesame, these eight oils are the most widespread in the food supply and have even been dubbed the “hateful eight.” They’re the ones usually named in claims that seed oils are “toxic” and detrimental for health, receiving blame in internet spaces for countless health issues from obesity to cancer.
How are seed oils made?
Seed oils typically go through a series of processing steps to be turned into the bottles you see on store shelves. Some oils undergo mechanical cold or expeller pressing, which involves pushing the seeds through a press using friction to extract the oils. Some heat is created through expeller pressing, whereas cold pressing is more controlled to keep temperatures from getting too high.
Seed oils that are not labeled as expeller or cold pressed usually go through more intensive chemical processing to extract oil from the seeds. Canola oil, for example, is cleaned, heated, pressed, and then soaked in a hexane-based solvent that eventually evaporates. Then, it’s refined to improve shelf life, odor, color, and flavor.
Claims against seed oils
Critics of seed oils claim that negative health effects stem from their processing as well as their composition. They often suggest that intensive processing may strip the oils of nutrients, introduce harmful chemicals, and leave behind trace amounts of hexane, a toxic gas.
In addition, many seed oils contain high amounts of polyunsaturated omega-6 fatty acids. The most common omega-6 in seed oils, linoleic acid, is essential for health but may have pro-inflammatory effects when consumed in excess. It’s been claimed that since seed oils are widespread in the food supply, humans are eating much more omega-6 fatty acids than they did throughout history. At the same time, modern diets do not contain enough omega-3 fatty acids like those found in fatty fish.
Some scientists suggest that eating too many omega-6 fatty acids and not enough anti-inflammatory omega-3 fatty acids results in chronic inflammation associated with many diseases. In other words, the ratio of omega-6 to omega-3 found in today’s typical Western diet may be part of the reason for the increase in diet-related diseases.
Finally, the processing and nutritional composition of seed oils makes them prone to oxidation. When exposed to high heat, light, or oxygen, polyunsaturated omega-6 fatty acids undergo reactions that may release potentially harmful compounds and make oils go rancid. This is why critics of seed oils often suggest that using them for frying and high heat cooking, especially over and over again, causes “toxins” to form.
What the science says
Overall, the seed oil debate lacks a robust base of evidence to back up the many suggestions that they are uniquely bad for human health. There is no recent, strong research that supports the theory that linoleic acid causes inflammation and is detrimental to health. It’s also unclear what ratio of omega-6 to omega-3 fatty acids in the diet would even be ideal for health. Claims about the negative impact of compounds added during chemical processing and created through oil oxidation on human health, while seemingly possible, are not supported by any randomized controlled trials.
As pointed out in recent studies, the way fatty acids behave in the human body is complex. While the theory that eating too much linoleic acid leads to the development of inflammation in the body may make sense on the surface, the way it actually plays out in the body is hard to predict or study.
A meta-analysis of 30 randomized controlled studies found that linoleic acid consumption does not affect markers of inflammation in the blood. Instead, research suggests that omega-6 fatty acids like linoleic acid may be beneficial to heart health.
As research continues, it’s possible that conclusions about the impacts of seed oils on health will change. Concerns about the negative health effects of the chemical processing, composition, and oxidation of these oils should continue to be explored. But at this moment, the science is not clear cut.
Putting it all together
At the end of the day, the evidence behind the vilification of seed oils is not strong. However, that doesn’t mean you should be racing to include them in excess in your diet. Seed oils are often found in ultra-processed and fast foods, two categories that should be limited in a well-balanced diet.
Instead of focusing on avoiding them at all costs, turn your attention to eating more whole and minimally processed foods like fruits, vegetables, whole grains, legumes, and lean meats. A healthy diet should mostly consist of foods that naturally do not have seed oils or other additives anyway.
To meet your omega-6 needs, consider consuming whole nuts and seeds instead of their oils. These have not been heavily processed and still contain fiber, protein, and other beneficial compounds that aren’t found in seed oils. Choose raw or dry roasted options, since many roasted nuts actually contain seed oils.
For cooking, try extra virgin olive oil and avocado oil. These options are made from fruits instead of seeds, are not heavily processed, and maintain many beneficial nutrients and antioxidants. They are also both sources of heart-healthy monounsaturated fats.
Butter, lard, and beef tallow are often touted as superior options for cooking by the anti-seed oil crowd. However, these cooking fats are high in saturated fat. Eating too much saturated fat is associated with poor heart health outcomes. It’s probably best to use these foods sparingly and mostly rely on extra virgin olive oil and avocado oil as discussed.
Take-home message
Based on current research, consuming small amounts of seed oils on occasion is not going to have drastically bad impacts on your health. Claims that they are “toxic” and the root cause of all disease are overblown, but they aren’t really health foods either. Foods with seed oils tend to be heavily processed, deep fried, and/or high in sodium, sugar, or calories.
Instead of focusing on what to avoid, think about all of the foods with well-known healthful properties you can add to your 1200 calorie diet or diabetic meal plan. Fruits, vegetables, whole grains, whole nuts and seeds, lean proteins, and minimally processed dairy foods are excellent choices to keep you satisfied and feeling your best.
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