Avoiding seed oils is an online trend, but are they as bad as some would have you believe?

When United States secretary of health and human services, Robert F Kennedy Jr announced the new US dietary guidelines on January 7, he promised to "evangelise real food."

The 2025–2030 guidelines included a new food pyramid putting protein, saturated fats and whole foods in the spotlight.

According to Mr Kennedy, the guidelines aim to "end the war on saturated fats", encourage Americans to eat more protein and full-fat products and emphasise whole grains, reducing intake of refined carbohydrates.

Robert F Kennedy Jr has claimed seed oils are toxic.  (Reuters: Nathan Howard)

While seed oils are not specifically mentioned in the updated guidelines, Mr Kennedy has previously claimed seed oils were "poisoning Americans", and the new guidelines point to other types of oil and fats for cooking.

So what are seed oils and are they really the dietary villains that some people make them out to be? And what do the new guidelines say about saturated fat?

What are seed oils?

Seed oils (often sold as vegetable oils), as the name implies, are oils derived from seeds.

There are eight types that have been collectively referred to by critics as the "hateful eight"; canola, corn, cottonseed, grapeseed, rice bran, safflower, soy and sunflower. (Olive oil and coconut oil are classified as oils from fruits.)

These seed oils are readily available at supermarkets, typically affordable and often used in cooking thanks to some of them having a higher smoke point (meaning they can be heated to higher temperatures than other oils without smoking).

Canola oil is classifed as a seed oil as it is made from the seeds of the canola plant.  (ABC Landline)

Seed oils contain monounsaturated and polyunsaturated fats, which include omega-3 and omega-6 fatty acids.

Critics of seed oils claim they cause inflammation due to their high omega-6 content.

But Emma Beckett, a senior lecturer of nutrition and food science at Australian Catholic University, says a lot of claims against seed oils come from "nuggets of truth that are misunderstood".

Understanding omegas

Unsaturated fats are essential for life, but they can't be made by your body so you have to get them through your diet.

There are monounsaturated fats, and polyunsaturated fats, which branch into two types; omega-3s and omega-6s.

Omega-3 fatty acids are found in foods such as fatty fish and plant sources like chia seeds and walnuts, while omega-6 fatty acids are more commonly found in vegetable oils, seeds and nuts.

Traditionally it was assumed omega-3s had an anti-inflammatory effect, while omega-6 were thought to be pro-inflammatory. 

But Dr Beckett says this concept is outdated and over simplified.

"That comes from some old data that showed that you need omega-6s to create inflammatory mediators in the body."

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A recent study led by Daisy Crick from the University of Queensland's Institute of Molecular Bioscience shows the relationship between omega-3 and omega-6 is much more complex than previously thought.

"Surprisingly, although we expected to see an anti-inflammatory effect of omega-3 fatty acids, our results suggest that they also increased levels of some biomarkers of inflammation," Dr Crick says.

Her study also found that higher levels of omega-6 to omega-3s "could result in a chronic, albeit low-grade, inflammatory state."

But Dr Beckett says worrying about inflammation markers is "reductionist" and it is better to focus on the quality of foods eaten.

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Why is everyone suddenly talking about seed oils?

"More important is the inflammatory impact of foods high and low in omega-3s, and the inflammatory status of people with high and low omega-3 intakes; because foods with naturally occurring omega-3s will also be high in bioactive compounds that are anti-inflammatory," she says.

"This is why we can't assume supplements — specific and concentrated isolates, or highly processed foods with omega-3s as an ingredient, will improve health in the same way whole foods containing omega-3s will."

Clare Collins, a laureate professor in nutrition and dietetics at University of Newcastle, agrees.

"As a normal person, you have no chance figuring out what your ratio is, you're better off looking at what types of fats you use at home," Professor Collins says.