Is Vegetable Oil Unhealthy?

Vegetable oil has long been touted as a heart-healthy option, but recent research and discussion around vegetable oils, especially seed oils, have brought this into question. So, if you’re wondering if vegetable oils are a healthy or unhealthy choice, here is everything you need to know.

What is vegetable oil?

The term “vegetable oil” refers to any edible oil derived from plants. Any oil extracted from plant seeds, nuts, cereal grains, or fruit is considered a vegetable oil. Vegetable oils are generally mild, odorless, flavorless, and light-colored and are commonly used in cooking and food manufacturing (1).

Vegetable oil is not itself a type of oil, rather, it is a group of oils and the most popular vegetable oils include canola oil, corn oil, safflower oil, sunflower oil, and soybean oil. When a bottle of oil is labeled as “vegetable oil” it is either made of a single vegetable oil, typically soybeans, or a combination of vegetable oils. Vegetable oils also include a subset of oils known as “seed oils” which are derived from seeds.

Vegetable oils are sources of all fatty acids, including saturated, monounsaturated, and polyunsaturated fatty acids, however, their exact fatty acid composition varies based on the source plant and/or the processed techniques used in their production (2, 3).

How are vegetable oils made?

Vegetable oils are made by extracting oil from plants using either a chemical solvent or an oil mill.

Vegetable oils were essentially non-existent until the early 1900s when new industrial processes allowed them to be extracted. Most vegetable oils require extensive processing to extract their oils. While the exact processing methods will vary by oil, the stages of refined vegetable oil production involve degumming, neutralizing, bleaching, deodorizing, dewaxing, and fractioning (4, 5).

List of Vegetable Oils and Seed Oils

Here is a list of the most common edible vegetable oils:

• Avocado oil
• Canola oil
• Coconut oil
• Corn oil
• Cottonseed oil
• Grapeseed oil
• Flax seed oil
• Soybean oil
• Safflower oil
• Rice bran oil
• Olive oil
• Palm oil
• Peanut oil
• Sesame oil

Seed oils are a subset of vegetable oils that are derived from seeds and include (6):

• Canola oil
• Corn oil
• Cottonseed oil
• Grapeseed oil
• Rice bran oil
• Safflower oil
• Soybean oil
• Sunflower oil

Fatty Acid Composition of Vegetable Oils

Here is a breakdown of the saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) in common vegetable oils and seed oils (7):

Where are vegetable oils used?

Vegetable and seed oils are commonly used in the industrial food industry and are found in many ultra-processed foods. Refined vegetable oils are found in salad dressings, cereals, coffee creamers, cookies, crackers, granola bars, plant milk, popcorn, mayonnaise, and prepared meals, and are also used to make margarine, shortening, and fake butter or vegan spreads.

In addition to processed foods, vegetable oils, especially seed oils, are commonly used in restaurants, especially fast-food restaurants, as they are relatively inexpensive and highly versatile compared to other edible oils and animal fats. Moreover, many vegetable oils have a very high smoke point, which makes them great for deep frying.

In the past 100 years, vegetable oil consumption has dramatically increased in the Western diet at the expense of many traditional fats like butter and lard.

The Health Concerns of Vegetable Oils

While vegetable oils do have some potential health benefits, their drawbacks are concerning.

High in Omega-6 Fatty Acids

One of the main concerns with vegetable oils, specifically seed oils, is their high content of polyunsaturated fatty acids (PUFAs), namely omega-6 fatty acids.

Both omega-3 and omega-6 fatty acids are essential fatty acids that cannot be produced by the body and, therefore, must be consumed through the diet. These PUFAs have been shown to have numerous health benefits, however, the ratio in which they are consumed is important.

Studies of evolutionary diets have shown the optimal ratio of consumption of omega-6 to omega-3 fatty acids is somewhere in the range of 1:1 to 4:1 (8, 9). Unfortunately, due to the increased consumption of vegetable oils and the processed food products that contain them in the Western diet, this ratio has dramatically increased and has been seen as high as 20:1 in some cases (10). This increase has been correlated with increases in chronic inflammation and impaired gut health (11, 12).

Some studies have shown that a high intake of omega-6 fatty acids is associated with an increased risk of heart disease, however, other studies do not support this idea. In fact, a high consumption of linoleic acid, the most common omega-6 fat, has several health benefits (13).

Omega-6s are the PUFAs found in vegetable oils, and although they are essential to human health, in excess they may be harmful and inflammatory, however, further study is needed.

Trans Fats

Certain commercial vegetable oils contain trans fats, which are considered harmful to health.

While trans fats naturally occur in many animal foods, most of the trans fats in the Western diet come from partially hydrogenated oils (PHOs), which are formed through a manufacturing process that converts vegetable oil into solid fat at room temperature (14). A high intake of trans fats has been associated with many chronic diseases, including heart disease, obesity, cancer, and diabetes (15).

Trans fats have been banned in many countries, including the United States since 2015, however, in some places, it can be difficult to avoid them fully. Currently, the FDA still allows food manufacturers in the US to label their products “trans-fat-free” as long as there are fewer than 0.5 grams of these fats per serving (14).

Easily Damaged

Vegetable oils are easily prone to oxidation, which can cause the oils to go rancid.

Dietary fats differ in their chemical structure by the number of bonds they contain; saturated fats contain no double bonds, monounsaturated fats contain one double bond, and polyunsaturated fats contain two or more double bonds. differ by the number of double bonds their chemical structures contain.

Most vegetable oils are primarily composed of polyunsaturated fatty acids, and their high content of double bonds makes them more prone to oxidation (16). The double bonds in polyunsaturated fats in vegetable oil make them incredibly fragile and easily damaged by exposure to light, heat, and air.

Not only does the oxidation of vegetable oil damage the fat itself, but a high intake of polyunsaturated fatty acids in the diet and, therefore in your body, increases cell membranes sensitivity to oxidation. (17)

This susceptibility of vegetable oil to heat makes them a poor choice for cooking oils, as that is exactly what most households and restaurants use them for.

Refined and Highly-Processed

Most vegetable oils are highly refined and a form of ultra-processed food. The production of most vegetable oils is lengthy, technical, and requires many processing techniques. While food processing is not inherently harmful, many health-conscious consumers prefer to consume nutrient-dense whole foods, and it is generally advisable to prioritize unprocessed and minimally processed foods in the diet.

Moreover, certain vegetable oils use chemicals in the production process. Hexane is a chemical solvent used in the extraction of vegetable oils from seeds and grains. While it is removed in the refining process, traces of hexane residue may remain in the final product of these cooking oils.

That said, the hexane levels of vegetable oils and seed oils are nowhere near enough to cause toxicity, and hexane can be avoided by opting for expeller-pressed oil or cold-pressed oils, which are made without heat or chemicals (18).

Is olive oil a vegetable oil?

Olive oil is a fruit oil and is, therefore, a vegetable oil. However, unlike vegetable oils from seeds, olive oil is far less processed than other vegetable oils, as it is simply made by pressing ripe olives into oil. Moreover, olive oil, as well as avocado oil, contains a different fatty acid profile, containing fewer omega-6 fatty acids than other vegetable oils, especially seed oils.

Moreover, olive oil has been well-studied and has a large body of evidence to support its health benefits. (19, 20)

So, are all vegetable oils bad?

Not all vegetable oils are unhealthier, however, vegetable oils from seeds that are ultra-processed and particularly high in omega-6 fatty acids should be limited. This includes canola oil, corn oil, cottonseed oil, grapeseed oil, rapeseed oil, rice bran oil, and soybean oil.

Before industrial processing, humans simply consumed naturally occurring animal fats in the form of such as butter, ghee, tallow, and lard, or minimally processed fats such as olive oil. Although many people are still concerned about saturated fat, they need not be, as saturation of these fats is their most beneficial part.

Best Alternatives to Vegetable Oil

The best alternatives to refined vegetable oils are animal fats and plant oils that have been minimally processed. Natural cooking fats such as butter, ghee, tallow, lard, or olive oil are great for cooking and dressing. When buying liquid oils such as extra-virgin olive oil or avocado oil, look for versions sold in a dark glass bottle as light can turn oils rancid, and ensure they are stored in a cool, dry place away from heat sources.

How to Avoid Refined Vegetable Oils and Seed Oils

Here are some simple tips to limit your consumption of refined vegetable oils.

1. Don’t use them as cooking oil. To help reduce your consumption of refined vegetable oils and seed oils, when cooking at home, opt for higher quality cooking oils such as olive oil, and avocado oil, or use animal fats such as butter, ghee, or lard.
2. Read the ingredient list. When purchasing prepared foods, read the ingredients list and try to avoid products that include refined vegetable oils and seed oils. While this may be difficult to do for all products, many brands offer alternative options made of olive oil or avocado oil as opposed to canola oil and soybean oil.
3. Don’t stress too much. Given vegetable oils are commonly used in prepared foods and restaurants, there is no need to avoid them entirely, in fact, it is almost impossible.

In addition to solely focusing on limiting your consumption of omega-6 fatty acids, you can focus on consuming more omega-3 fatty acids in your diet to help balance out the ratio of essential fatty acids. Focus on consuming foods such as salmon, mackerel, sardines, flax seed, and walnuts, to help ensure you’re eating more omega-3 fats.

The Bottom Line

Vegetable oils are oils made from derived from plants and include a subset of oils known as seed oils which are derived from seeds. Certain forms of vegetable oils are refined and highly processed, are easily damaged by light, heat, and air, and contain high levels of omega-6 fatty acids, which may impact health negatively, however, more research is needed. It is best to limit the consumption of vegetable oils, namely seed oils, and prioritize sources of healthy fats such as animal fats and olive oil.