The Problem with Refined Oils: What Oils to Avoid in Your Kitchen

by | Mar 6, 2024 | Blog, General Wellness, Nutrition

Fortunately, by now, most people know that fat doesn’t make you fat. We don’t need to demonize them. Fats, or rather, healthy fats, are essential for your body.

Healthy fats can be found in both animal and non-animal sources, including avocados, avocado oil, coconuts, coconut oil, coconut milk, olives, olive oil, nuts, seeds, nut butter, grass-fed butter and ghee, grass-fed meat, pasture-raised poultry, wild-caught fish, and organic egg yolks. Healthy fats are much needed for your cell membranes, organ function, energy levels, hormonal health, and brain function. They are necessary for absorbing fat-soluble vitamins, including vitamins A, D, E, and K, and some minerals and antioxidants. A diet rich in healthy fats may help to keep your inflammation levels at bay, regulate your blood sugar levels, lower your triglycerides, and increase longevity (1, 2, 3, 4, 5).

Using oils in your cooking can be a great way to add healthy fats to your diet — and, of course, to improve the taste and quality of your dishes. They are an essential part of a healthy pantry.

However, what oils you use matters! Not all oils are created the same. Some oils, such as refined vegetable oils, are not good for your body, while other oils are healthy fats that may help to improve your health.

In this two part article, I want to first talk about the problem with refined oils in your kitchen. In part #2, I will go over the best oils to use in your kitchen instead.

The Problem with Refined Oils

Refined oils, also known as vegetable oils, are edible oils made from plants, used for cooking and baking. They are commonly found in processed foods, including margarine, salad dressings, sauces, cookies, baked goods, and mayonnaise. Some commonly known refined vegetable oils include soybean oil, canola oil, and safflower oil. 

Unlike olive oil, coconut oil, and animal fat, refined vegetable oils were not available until the 20th when the technology to make them became available. Refined vegetable oils are extracted from plants through an oil mill or with a chemical solvent and then get refined, purified, or even chemically altered at a factory.

You may be surprised to hear that these oils were not even made to be food at first. Back in the 1870s, William Procter and James Gamble, two soapmakers in Cincinnati, realized that they could make soap from vegetable oils instead of pork fat, which was used at the time. Using vegetable oils was much cheaper. Around the same time, cottonseed oil was used as a source of fuel as well, and they were able to get any leftover cottonseed oil for soap making. 

So, how did these refined oils become a food source? During their oil-making process, they realized that they could turn cottonseed oil into solid fat similar to the texture of lard through the process of hydrogenation. Eventually, corn, canola, soybean, safflower, and other vegetable oils were developed through similar processes and turned into a regular part of cooking, frying, food processing, and junk foods in the 20th century (6).

In the 1950s, Dr. Ancel Keys introduced the diet-heart hypothesis, suggesting a link between saturated fat, cholesterol, and heart diseases. Because animal fats are high in saturated fat and cholesterol, polyunsaturated fatty acids (PUFAs) became the new recommendation. Vegetable oils and margarine flooded the market, touted as healthy alternatives (7). The American Heart Association still talks about the benefits of PUFAs (8). Yet, more recent research indicates that PUFAs from vegetable oils have no heart health benefits (9, 10). As you will learn later in this article, they carry some health risks and are better avoided.

How Are Refined Vegetable Oils Made?

It’s a long and complicated process before refined vegetable oils end up in your kitchen or in our processed foods..

  • The first step is gathering all the seeds from corn, soy, rapeseed, safflower, or cotton plants.
  • Then, these seeds are heated at a very high temperature. This results in the oxidation of unsaturated fatty acids, as well as byproducts, which are toxic to both animal and human health.
  • Next comes processing with a petroleum-based solvent, which allows the extraction of the most oil from the seeds.
  • Because at this stage, most seed oils smell harsh, the next step is a deodorizing process that creates trans fats, which are rather harmful to your health.
  • As the final step, chemicals are added for color, then these refined oils are ready to be bottled up, sold at stores, or used in processed foods.

6 Reasons That Refined Vegetable Oils Are Unhealthy

Learning the history of refined vegetable oils and how they are made, chances are, you are already skeptical about their effects on your health. But let’s talk a bit more about 6 reasons why refined oils are unhealthy:

Evolutionary Conflict

You may approach this from an evolutionary perspective. Though our ancestors consumed nuts, seeds, coconuts, avocados, olives, and animal fats, they didn’t eat processed oils, which were introduced to our diet much later. Adding these refined oils, along with refined sugar and overly processed foods, only leads to an overweight and unhealthy society. In fact, a 2011 research has found that between 1970 and 200s, the average person’s weight has grown by 26 pounds (11). This is only getting worse. Though refined oils are not the only issue, they play a major role along with other processed, refined, and unnatural food sources, unhealthy lifestyle strategies, and stress.

Imbalances Omega 3:6 Ratio

Omega-3 and omega-6 fatty acids are both essential fatty acids. This means we need both — but we need them in a healthy balance. Omega-3 fatty acids offer anti-inflammatory benefits. However, omega-6s are pro-inflammatory. Refined vegetable oils are high in omega 6s, and following a diet high in them may disrupt the balance. The healthy ratio of omega 3 and 6 is between 1:1 and 1:4, but due to our modern diet high in refined oil and other unhealthy ingredients, we see 10:1, 20:1, or even higher ratios, which may lead to chronic inflammation, chronic symptoms, and chronic diseases (12).

Unstable Oils

Refined vegetable oils are incredibly unstable and oxidize easily when they are exposed to heat, chemicals, or light. These factors can lead to the development of trans fats and lipid peroxides. Trans fats may increase the risk of cardiovascular disease and type 2 diabetes, and lipid peroxide may disrupt your DNA, membrane lipids, and proteins. Both can increase the risk of chronic disease and lead to early signs of aging (13).

Heat and Toxicity

Whether you are cooking with them at home or they are used at fast food chains or restaurants, refined oils are often heated repeatedly.  Frequent reheating can lead to the release of toxic byproducts, which may harm your health. It can also rob them of any remaining natural antioxidants. It also leads to the formation of free radicals, which increase oxidative stress, chronic inflammation, cardiovascular disease, digestive issues, and chronic health problems (14, 15, 16).

Synthetic Additives

Refined vegetable oils tend to be very unstable. To reduce this issue, during production, they add synthetic antioxidants to lower the risk of oxidation and rancidity. These synthetic antioxidants may have endocrine-disrupting, immune-disrupting, and carcinogenic effects and may also cause food allergies, food sensitivities, inflammation, and other health issues (17, 18, 19).


Finally, though not all, the majority of refined vegetable oils come from genetically modified (GMO) sources. In the United States, around 90% of soy, corn, cotton, and rapeseed have been genetically modified. GMO products are also a major issue in Canada, while less so in Europe. While we still need more research to completely understand the potential long-term safety and risks of GMOs, avoiding them certainly seems like the safest choice (20, 21, 23, 24, 25).

Diseases Linked to Refined Vegetable Oils

Refined vegetable oils may increase your risk of certain health issues, including:

  • Asthma (26)
  • Obesity (27)
  • Chronic inflammation (28, 29)
  • Diabetes (30, 31)
  • Heart disease (32)
  • Anxiety, depression, and mental health issues (33)
  • Cognitive decline, dementia, and Alzheimer’s disease (34, 35)
  • Irritable bowel syndrome (IBS) and irritable bowel disease (IBD) (36, 37, 38)
  • Infertility (39, 40)
  • Osteoarthritis (41)
  • Macular degeneration (42)

Oils to Avoid in Your Kitchen

Refined vegetables that I recommend you avoid in your kitchen include:

  • Corn oil
  • Canola oil
  • Rapeseed oil
  • Sesame oil
  • Soybean oil
  • Sunflower oil
  • Safflower oil
  • Peanut oil
  • Rice bran oil

In short, I don’t recommend using any oils besides olive oil, coconut oil, avocado oil, and flax oil. Why do I recommend these four oils? Now that you understand the health risks of refined vegetable oils, you probably want to know what are best oils to use in your kitchen.

In part #2 of this article series, I will go over the best oils to use in your kitchen.

Next Steps

If you want to know more about how nutrition and cooking strategies may improve your health, follow my blog or schedule a consultation for personalized advice.

If you are dealing with any chronic health issues and need advice on how to improve your nutrition and health, I welcome you to start a functional medicine consultation with me for further personalized guidance. You may book your consultation here

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