Are Seed Oils Bad for You?

Seed oils are a controversial topic.

One of the main reasons I want to address them is that it’s a space where people often talk very negatively. And then there are people on the other side who are either saying that seed oils are not bad, or in some cases might even be “heart healthy.”

The goal of this post is to unpack the entire discussion in what I would consider a balanced fashion.

Is there truth to the negative claims? And if so, have some of them been “stretched” to sound a bit worse than the reality?

Is there truth to the positive claims? And if so, should we go out of our way to add them into our diet if we are not currently having them?

Those are some of the questions I want to answer.

You may or may not agree with my conclusions. But I am mostly writing this for the people who personally care about what I have to say about big nutrition topics.

If you just want my short interpretation without any nuance, feel free to scroll to the bottom.

Defining Seed Oils

Seed oils are oils that are extracted from the seeds of various plants.

Common examples include soybean oil, sunflower oil, canola oil, and safflower oil.

These oils are typically high in polyunsaturated fatty acids, such as omega-6 fatty acids.

They are often used in cooking, food processing, and as ingredients in a wide range of products.

Processed vs Unprocessed Seed Oils

It is worth noting before we get into the section about the negatives surrounding seed oils that there are multiple ways of producing seed oils.

I’ve previously written about “extra virgin olive oil” vs regular olive oil. The extra virgin version is simply produced by cold-pressing olives without the use of heat or chemicals.

Similarly, it is possible to produce seed oils without heat or chemicals.

While some arguments might still apply, I’d wager most people would be less concerned about cold pressed oil coming from things like:

• Sunflower seeds
• Flaxseeds
• Sesame seeds
• Pumpkin seeds

But most seed oils consumed in the population’s diet typically come from more processed versions that will be discussed later.

Why Are Seed Oils in the Diet?

Many people tell stories about why seed oils are in the diet. And these stories are often done in a way that leads to the conclusion that they are bad.

I’ll take a different angle and just list some things that I think are factual reasons:

• They are cheap to produce. This is relevant for when people are buying oil AND also for the fact that are added to many common food products.
• They have high smoke points, which could be of interest to certain people in relation to cooking.
• Taste reasons. Some have a more neutral flavour. Others might just improve the taste, as perceived by certain people.
• Seed oils are high in polyunsaturated fats. Traditionally, people view “good” fats as monounsaturated and polyunsaturated and “bad” fats as saturated and trans fats.
• Due to the above belief, many people try to avoid certain fats/oils that are high in saturated fat and want an alternative that is not.
• They have a relatively long shelf life.

There are many more. I just tried to make a concise list without adding any personal thoughts.

Without clear evidence (since self-reported data has flaws), people have estimated that seed oils make up 7-8% of total calorie intake of the population of those living in America. I live in Australia, but I feel like American estimates are still relevant here to a degree too.

What are the Negatives Proposed?

I am going to go back and forth by putting up each of the common claims I want to address, and then adding a bit of a response to each.

“Have you seen how they are made? I don’t need to see anything else. They clearly can’t be good for you”

For starters, if you want to see how they are made, I think a great place to start is to watch this:

This video has 4.2 million views. Although the video is made as if it is trying to promote canola oil, the comment section looks exactly like you would expect it to.

That video is on canola oil, but a quick summary on most seed oils is that the process looks like the following:

1. Seeds are gathered.
2. They are heated to extract the oil.
3. A solvent such as hexane is used to maximise extraction from the seeds.
4. Sodium hydroxide is added to neutralise free fatty acids that contribute to off-flavours and instability.
5. The seed oil is deodorised to mask the off-putting smell. This often involves high heat too.
6. The oil is then bleached to make the colour more appealing to consumers. This is often done using heat in combination with absorbent clays and activated charcoals.

This doesn’t sound overly appealing, particularly in comparison to the cold pressed version described earlier without heat or chemicals.

Critics of this process often highlight the following:

• The heating process reduces the antioxidant content and leads to oxidation of many of the fatty acids.
• Hexane is petroleum-based and is also a known neurotoxin.
• There are many chemicals added to the process that could potentially be harmful.
• The deodorisation process can cause the production of trans fats.
• Some people claim the bleaching process involves chlorines, but that doesn’t appear to be common. Even without that though, bleaching does still reduce the vitamin and antioxidant content.

An attempt at a balanced response to the criticisms:

• The heating process does reduce the antioxidant and vitamin content. The extent of the oxidation and the health implications depends a bit on the temperature and duration.
• While hexane is a dangerous ingredient, it is removed from the final product. The traces left behind are very low, which is why they are considered safe by regulatory agencies.
• In relation to chemicals: The dose makes the poison.
• The trans fat content is almost always <1% of the total fat content of the oil.
• Similarly to hexane, the same logic applies to the components used in the bleaching component.

The processing aspect does not look great. I see why people would hold this opinion.

My personal perspective is that it makes sense to factor in the processing aspect AND all the other aspects to be discussed below too.

“Seed oils are a recent addition to the human diet. We are not evolutionarily equipped to consume them”

I am largely just going to leave this criticism here, and you can make of it what you will.

There is logic to it. But I personally take a slightly different perspective in that if we have a lot of evidence on the topic, I’d prefer to focus on the evidence.

Theoretically it’s possible for something to be a recent addition and either be beneficial, or at least not detrimental. This line of thinking would make us avoid those beneficial things too.

I could use a lot of arguments that fit that description. But instead, I will just continue with the next points.

“Seed oils are high in omega-6s. Humans should have 1:1 ratio of omega-6s to omega-3, but typically have a 5:1 to 20:1 ratio”

There is some portion of truth here, although it is not as clear-cut as some might make it seem.

Part of this argument is based on that same evolutionary discussion as well.

Some weaknesses of this criticism are:

1. How do different levels of consumption affect this? If you had a high intake of both, the ratio is the same as if you had a low intake of both.
2. The ratio partly implies that omega-3 is good, and omega-6 is bad.
3. The ratio alone doesn’t account for food sources.

It is clear that omega-3 fatty acids have benefits.

The level of benefit is individual and depends on the circumstances. Some people highlight individual studies that have not found much benefit. But as a broad overview of the evidence, it is not controversial to say that omega-3 fatty acids are beneficial.

Based on ratio logic though, there should be clear evidence that adding more omega-6 causes issues though.

There are mixed findings.

A massive analysis looking at biomarkers found that higher levels of omega-6 were linked with lower cardiovascular disease risk. If the ratio mattered a lot, this finding seems very unlikely.

From another angle, while people often claim that saturated fat is bad for heart health and unsaturated fat is good, this meta-analysis found no difference.

This is a huge topic, and I could go deeper into the research, but a simple next step is to look at food sources.

Nuts and seeds are high in omega-6 AND they are consistently linked with positive health outcomes.

If the ratio mattered a lot, this would be unlikely. Or alternatively, you could just argue that the other beneficial components in nuts and seeds matter more.

Linking this back to seed oils, a balanced take could be that:

• Whether or not the omega-6 to omega-3 ratio matters much, a large percentage of the population would benefit from increasing their omega-3 intake.
• Food choices matter. Nuts and seeds are consistently linked with positive health outcomes. They have many other beneficial components such as vitamins, minerals, and fibre.
• If you have a large intake coming from highly processed foods that are low in micronutrients, it makes more sense to reduce it. Most seed oils fit into this category.

“Obesity was rare before seed oils were introduced into the food supply”

The above image is a classic example of this criticism.

But is this due to seed oils? Or a combination of variables?

Over the last 70 years, a LOT has changed.

• Jobs have become more sedentary due to technology.
• Household chores used to require more physical activity than they often do now, also due to technology.
• Other aspects of physical activity have reduced due to a variety of things competing for attention. The improvement in entertainment can make physical activity less appealing than it previously would have been for many people.
• Calorie intake has increased. It hasn’t increased enough to fully explain the change. But when you add in the calorie expenditure reduction due to changes in physical activity, it adds up.
• We previously had less access to hyperpalatable food. For example, even the addition of things like Uber Eats makes it so that people no longer need to even leave the home or speak to people when ordering.
• Food marketing has improved dramatically. Analytics and technology play a big role in this too. For example: Self-serve checkouts at places like McDonalds are designed in ways to optimise for upsells.

I could make a massive list.

To focus on seed oils here in isolation would be wild considering how many variables play a role.

Do seed oils play a role? For sure. Even if you simplified down to calories in and calories out, they play a large role.

A large percentage of the foods that are considered hyperpalatable foods contain seed oils.

There’s a reason they make up ~7-8% of the calories reportedly consumed in the American diet.

If somebody were to stop eating seed oils, they would also need to stop eating a lot of the commonly consumed ultra-processed foods including many fast-food places, cakes, biscuits, chocolates, and many other things.

Doing that is highly likely to reduce calorie intake.

Are There Any Positives?

Specifically, from a health perspective, there are some potential positives. But these positives are largely only relevant if:

1. Consumed in moderation.
2. Consumed in a more minimally processed form.

The benefits can be:

• Vitamin E content and other antioxidants (if not destroyed by processing).
• Flaxseed oil is particularly high in omega-3. This form of omega-3 (ALA) is not as easily converted as the omega-3 in fish, but it’s still beneficial.
• If somebody were to otherwise have a low omega-6 intake, there are benefits of adding it in. It is still quite literally an essential fat.
• Some seed oils have anti-inflammatory properties. Flaxseed oil is another one that is commonly linked with this.
• Although this might seem controversial, research has consistently found that replacing saturated fat with polyunsaturated fat reduces cardiovascular disease risk.

All these benefits can be achieved in other ways. But I figured it was worth adding something to balance the article out a bit more.

Interpretation

A lot of the negative attention given to seed oils is arguably overblown. That said:

• They are often highly processed.
• Oil is very calorie dense in general.
• After the processing aspect, seed oils are often quite low in micronutrients.
• They are also high calorie.
• Seed oils are commonly found in hyperpalatable processed foods that are consistently linked with poor health outcomes. Reducing intake of these things typically would lead to better health outcomes.
• While it’s debatable how much the omega-6 vs omega-3 ratio matters, there is an argument to be made that 1) Increasing omega-3 intake is typically a good idea 2) Reducing intake of processed sources of omega-6 if it is currently high can make sense.

In relation to that last point, even if you viewed these oils as “neutral” it’s food for thought what could happen with “replacement.”

Example: If currently 7-8% of the calorie content of the American diet was coming from seed oils, what would happen if that was reduced to 3-4% on average, with it being replaced by other more nutrient rich, unprocessed foods?

Succinct Consensus

While the negativity surrounding seed oils is a bit overblown, they also aren’t something I’d typically recommend people try ADDING.

If you had a high intake of these things, particularly the refined/processed versions (which are most common), it likely makes sense to reduce that. If that intake is coming as part of other refined/processed foods, it likely makes sense to reduce those in general anyway.

A low intake of these things likely is not a big deal. It’s just that right now, statistically speaking, at a population level, intake of seed oil is quite high. Theoretically, replacing this with other nutrient rich options likely would have benefits.