What are seed oils, and should you avoid them?

Seed oils are oils derived from the seeds of plants, such as grapeseed (canola oil), soybean oil,  cottonseed oil, and others. These oils have been used in culinary applications for a long time due to their low cost and versatility in cooking.

However, there are some potential drawbacks to using seed oils. Recently, people have become more aware of the fact that not every cooking oil affects your health the same way. Sure, a gram of cooking oil amounts to a gram of dietary fat, but there are other ways that different oils differ aside from macronutrient counts.

Here are a few things you should be aware of when it comes to seed oils.

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Are seed oils bad for you?

Seed oils aren't inherently bad on their own, but there are some things you should be aware of when deciding which culinary oils to use. Fatty acid breakdown, extraction methods, and time on the shelf all contribute to the quality of an oil.

Fatty acid breakdown

One major concern around seed oils is the higher levels of omega-6 fatty acids found in these oils. While omega-6s are necessary for our bodies, the typical Western diet already contains a high ratio of omega-6 to omega-3 fatty acids. This imbalance might lead to inflammation and other negative health effects.

It's not the amount of omega-6 that matters as much as the ratio of omega-6 to omega-3 you're getting through diet. In our society, it's simply easier to get omega-6 fatty acids in the typical foods we eat. You can balance out these effects by making sure you're getting omega-3 fatty acids as well, either through diet or supplementation.

Seed oil extraction methods

Another reason people are paying more attention to the source of their oils is because of extraction methods. Two main extraction methods are used with seed oils: solvent extraction and high heat extraction. Neither is ideal.

Solvent extraction

Solvent extraction involves using hexane. According to the EPA, inhalation of hexane could affect the central nervous system and you may experience dizziness, giddiness, slight nausea, and headache. This is direct exposure to the chemical, not so much the kind of exposure you'd get through eating oil extracted with hexane. Still, some people choose to avoid it.

High heat extraction

Many seed oils undergo a process called "high heat extraction," which involves using high temperature and pressure to extract the oil. This can lead to oxidation, which can be harmful in certain amounts.

Excessive oxidation could lead to cardiovascular disease, joint problems including arthritis, digestive conditions, cell damage, and other problems.

Shelf life

Once a seed oil is in the bottle, it might hang out on the store shelf for a long time. Oils slowly oxidize over time, so the older an oil is, the more potentially oxidized it might be.

This applies to all oils, although some are more stable (resistant to oxidation) than others. Your best bet is to choose the freshest, most stable cooking oil you can get your hands on. 

While seed oils may have their uses in the kitchen, it is important to be mindful of their potential drawbacks and consume them in moderation. Opting for healthier alternatives like olive or avocado oil can benefit both your health and taste buds.

References

Hexane - US EPA. https://www.epa.gov/sites/default/files/2016-09/documents/hexane.pdf. Accessed October 26, 2022. 

Grootveld M, Silwood C, Addis PB, Claxson A. (PDF) Health effects of oxidized heated oils - June 2006 Foodservice Research International 13(1):41 - 55

DOI:10.1111/j.1745-4506.2001.tb00028.x

https://www.researchgate.net/publication/229976090_Health_effects_of_oxidized_heated_oils