Are Seed Oils Safe and Healthy for Consumption?

Janet Tiberian Author
By Janet Tiberian, MA, MPH, CHES
September 20, 2022
Oil poured into a blue stovetop pan

The topic is surprisingly polarizing among nutritionists, foodies and many health advocates. What are seed oils? Are seed oils bad for you? Are cooking oils made from seeds like canola or soy healthy and safe?

The oils, which have been a staple of western diets for more than 100 years (oil made from soybeans goes back thousands of years in Eastern diets), seem innocuous enough. We use them in baking and frying, and food manufactures use them in everything from mayonnaise to cookies. They have soared in popularity at the expense of butter and lard, once the main source of cooking fats in American diets.

They are often seen as heart-healthy – at least more heart healthy than the fats they replaced. And they are cheap compared to other alternatives like olive oil. 

There are many seed oils, but the most common ones include: 

  • Canola 
  • Corn 
  • Cottonseed 
  • Soybean 
  • Sunflower 
  • Safflower 
  • Grapeseed 

Vegetable oil is typically a blend of 1 or more of these oils. People began using seed oil in the early 20th century as an alternative to lard. Today they’re commonly used for baking, cooking and as an ingredient in processed foods. They remain popular because they’re:

  • Affordable
  • A good source of antioxidants and vitamin E
  • Able to help lower cholesterol and blood sugar levels

None of this sounds controversial. But it is.

How Seed Oils Are Processed

Part of the controversy revolves around how seed oils are created. Before discussing the manufacture of seed oils, it’s useful to look at how olive oil is made. Olive oil, which is held up is one of the healthiest oils, is typically made with a mix of ancient techniques and modern technology. Olives and pits are crushed into a paste to release oil, then slowly stirred with water so that the oil clumps; they have been processed this way for more than 1,000 years. 

Modern producers do this in closed mixing chambers filled with inert gasses to reduce oxidation, which can change the flavor of the oil. They may also add a little heat to improve oil extraction. The subsequent oil is typically labeled extra virgin olive oil. It’s healthy, simply processed and 4-5 times the cost of canola and soy oils.

Extracting oil from seeds is different. Like olives, seeds are heated, milled, squeezed, heated and pummeled until the oil is extracted. Manufacturers also use the chemical solvent hexane to maximize the extracted oil. (Some olive oils actually use hexane, too, but these oils are not typically labeled extra virgin.) 

Once extracted, manufacturers use other processes to enhance:

  • Flavor
  • Color
  • Stability

Water and organic acids may be used to remove fine meal particles and fats. The oil may be passed through filtration, a process that’s unfortunately called bleaching, though it does not involve bleach.

Although some seed oils are processed similarly to olive oil (and those that are expensive), most brands at the grocery store are highly processed. 

Are seed oils safe?

That doesn’t make them unsafe. In fact, the Food and Drug Administration considers them safe for human consumption and even allows some health claims. Canola oil, for example, is considered “healthy” because it is very low in saturated fat and high in monounsaturated fat. It also contains some omega 3 fats. 

Opponents of the oils, however, often point to their highly processed nature and hexane as one of the reasons the oils should be avoided. Hexane is a solvent that is used to improve oil extraction in the manufacturing processed; most of it is removed by the time the oil reaches the store. Hexane is not harmless like the gasses used in olive oil production, but it has a very low toxicity. It’s been used for nearly a century to extract oil, and there is no evidence that it’s harmful in the trace amounts found in processed seed oils.

In fact, you probably ingest more hexane while pumping gasoline.

So, what’s the problem with seed oils? 

Just because seed oils are not considered unsafe by the FDA, doesn’t mean that they are “healthy.”

Seed oils may contribute to inflammation, raising the risk for various diseases and weight gain. However, healthy experts are really divided. One camp suggests you eliminate industrial seed oils from your diet, while the other believes there’s not enough evidence to support this suggestion. 

To unpack the connection between seed oils and inflammation, you need to understand unsaturated fats. Fats are broken into 2 umbrella groups -- saturated and unsaturated. There are chemical differences between the two types of fat, but the simplest explanation is that saturated fats are solid at room temperature and include animal fats like butter and lard and plant fats like coconut oil. Unsaturated fats which are generally liquid at room temperature – like oils.

Unsaturated fat also can be broken into 2 groups – trans and cis. Let’s start with trans fats and then we’ll tie everything back to seed oils.

Trans fats can be found in small amounts in animal products, but most often, they’re lab created. Manufacturers add hydrogen to an oil, solidifying it to make products like vegetable shortening and margarine. The process is called hydrogenation, and originally, hydrogenated fats were created to help us lower saturated fat consumption. However, over time, studies found that hydrogenated (or trans) fats are more harmful than saturated fats; they trigger inflammation, raising your risk for:

  • Pain syndromes
  • Asthma
  • Cancer
  • Heart disease 
  • Type 2 diabetes
  • Certain types of arthritis

Cis fats can be either monounsaturated (omega-9 fatty acids) or polyunsaturated (omega-3 or omega-6 fatty acids). All these types of fat are necessary for health. But we acquire them differently. 

Your body can produce omega-9 fatty acids. But you also can get these fats into your diet by eating nuts and nut oils. 

However, your body cannot produce omega-3 or omega-6. These fats must come from foods. Examples include:

  • Salmon
  • Mackerel
  • Sardines
  • Chia seeds
  • Walnuts
  • Sunflower seeds
  • Almonds
  • Corn oil 

There should be a healthy balance between omega-3s and omega-6s. The ideal ratio of omega-3s to omega-6s is one to four. This means you should consume between 1.1 and 1.6 grams of omega-3s and up to 6.4 grams a day of omega-6s per day. The remainder of your fat consumption would be a combination of monounsaturated and saturated fats, according to The Dietary Guidelines for Americans 2020-2025.

Omega-3s help reduce inflammation while some omega-6s foster it, specifically, linoleic acid, an essential fatty acid that’s needed for healthy cell membranes and skin. Too many omega-6s can lead to chronic inflammation, potentially causing health issues. 

Unfortunately, maintaining a healthy ratio is easier said than done. The typical Western diet has about 10 times more omega-6s than omega-3s. Most Americans are eating between 5 and 15 times the recommended amount of omega-6 fatty acids, according to a study published in Progress in Lipid Research. These extra omega-6s are coming from seed oils in processed foods. Processed foods comprise about 70 percent of the American diet and our consumption of ultra-processed foods continues rising.

In processed foods, these seed oils are often partially hydrogenated and convert into trans fats. Although most food manufactures have replaced partially hydrogenated oils with other ingredients, many foods are still made with them.

Why aren’t these oils banned?

These oils remain unbanned because the actual health impact of trans fats, lipid peroxides and highly processed seed oils aren’t clear. In fact, some researchers reject concerns over the health of seed oils, claiming the studies that suggest seed oils may not be healthy were poorly conducted.

These researchers assert that linoleic acid usually contributes to lowering inflammation and the risk of inflammatory diseases like heart disease. A meta-analysis of 30 studies found that participants with higher linoleic acid levels in their blood were seven percent less likely to develop heart disease. And men with the highest levels of linoleic acid had a 43 percent lower risk from dying from any disease compared to men with the lowest levels of linoleic acid, according to a study published in the American Journal of Clinical Nutrition.

Are you torn?

Don’t be. Nutrition science is often complicated and somewhat controversial. But there’s something to take from the controversy: Seed oils often end up in foods we should eat less of anyway, namely, fried and highly processed foods. Using them occasionally in home baked goods or other recipes is probably okay. If you are concerned about limiting your use, try these suggestions:

  • Skip ultra-processed foods. Many ultra-processed foods are linked to health issues. Some of these foods can easily be swapped with a homemade version. For instance, replace commercial salad dressings with an olive oil and lemon juice mixture.
  • Try an air fryer. We’re not advocating to eliminate cooking oils from your diet. But if you’re looking to cut back, air fryers can provide an oil-free method of cooking.
  • Eat healthy fats. Healthy fats are necessary for good health. You can find them in avocados, olive oil, nuts, seeds, eggs, fatty fish (like salmon) and lean beef and poultry. 
  • Talk to your doctor. Your doctor knows your health history and can help guide your dietary decisions and/or refer you to a specialist. Get more knowledge to answer the question "Why are seed oils bad for your health?" and receive guidance navigating a seed oil diet for your lifestyle. 

Don’t have a doctor? Consider partnering with an MDVIP-affiliated physician. They have time to really work with you and develop a wellness plan. Find a physician near you and begin your partnership in health » 

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About the Author
Janet Tiberian Author
Janet Tiberian, MA, MPH, CHES

Janet Tiberian is MDVIP's health educator. She has more than 25 years experience in chronic disease prevention and therapeutic exercise.

View All Posts By Janet Tiberian, MA, MPH, CHES
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