Untangling the Seed Oil Debate - WARNING: Don't Read if You Like Your Echo-Chamber

It’s one of the keystone issues for the #MAHA movement. But this is not just about French fries. It's about something larger: how we dissect conflicting data in nutrition.

Acknowledgement

I spoke with other science communicators (“influencers,” or use whatever word you choose) in composing this letter, including Mark Hyman, Paul Saladino, and Nic Verhoeven (Physionic YouTube Channel). Each provided references, input and/or feedback that was included in this letter in some form, and I look forward to ongoing conversations with each about this particularly controversial topic.

In fact, I’m releasing this letter now, rather than late July as originally planned, because I have a conversation planned with one of these men next week and thought community feedback would be ‘interesting’ fodder for our discussion. This may end up being a living document…

RFK Jr. Declares Seed Oils are “One of the most unhealthy ingredients we have in foods”

One of the most heated and fascinating debates in the nutrition space right now is that of “seed oils.”

It’s one of the keystone issues for the “Make America Healthy Again” #MAHA movement. For example, Robert F. Kennedy Jr., who calls the seed oils in which fast food chains now cook their French fries, “one of the most unhealthy ingredients we have in foods.”

This has led to a counterculture movement to replace industrialized plant-sourced fats, i.e., “seed oils,” with animal fats. There are cries to “Bring Back the Tallow Fries” to fast food chains like McDonald’s—the dietary version of “Make Fries Great Again.”

Restaurant chains are responding, literally “RFK’ing the fries,” meaning trading the seed oils for tallow for presumed health benefits.

But this isn’t really an issue or video about French fries. It’s about something much larger and more important: It’s about how we dissect conflicting data in nutrition.

The reason there is such profound confusion on the topics of animal vs. plant fats and “seed oils” is because different sources of evidence make opposing arguments, and each side thinks their argument is best.

Rather than try to resolve the inconsistencies, we dismiss and bicker.

But in this letter (minus an intentionally provocative thumbnail), we will begin to dive into the nuances of this issue. Don’t jump to conclusions until you reach the end. You may agree with me more than you think…

Roadmap

• Physiological Rationale: I want to discuss the physiological rationale for why seed oil fries are presumed to be harmful, and why tallow fries might be better.

• Human Trial Data (Not So Fast!): Building on this French fry case in point, I want to expand the discussion to the human trial data on omega-6 fats and cardiovascular disease.

• Resolving Contradictions: Then, we will resolve the apparent contradictions that emerge.

• Making Smart Choices: Finally, I’ll close by telling you what I think is practical and reasonable when it comes to handling fries, nuts, cooking fats, and making your food choices healthy (again?).

Seed Oil Fries – Worse than Cigarettes?

There are influencers claiming foods cooked in “seed oils,” including but not limited to seed oil fries, are worse than smoking cigarettes. I know, it’s a bold claim! What’s the basis for this argument?

Well, many plant fats are rich in fragile omega-6 polyunsaturated fatty acids (PUFA). Chief among these is linoleic acid (LA), an 18-carbon unsaturated fat with 2 double bonds.

When heated, PUFA like LA are highly susceptible to a form of molecular damage called oxidation, which can transform them into biochemically harmful substances called lipid oxidation products, including aldehydes and other compounds that are known “cytotoxic” (harm cells), “genotoxic” (harm DNA), and carcinogenic (cause cancer).

Saturated fats, which make up a larger proportion of tallow, are relatively more stable to heat and do not form these lipid oxidation products as easily. You can see that by comparing these graphs of sunflower oil (considered one of the “Hateful 8” seed oils) on the left versus butter (rich in saturated fat) on the right. The lines represent formation of aldehydes generated over time when heated at 180°C (356°F), at or below the temperature of a deep fryer. Clearly, there is more aldehyde formation in the heated “seed oil” versus the animal fat, be that butter or tallow.

But just how big is the problem?

Well, the maximum human daily intake for one aldehyde, acrolein, is 525 micrograms, according to the World Health Organization. But just one standard restaurant serving of potato chips (154g) can contain 1,000 – 1,500 micrograms of this toxic substance, a dose on par with smoking 25 cigarettes per day.

I’m not endorsing the equivalency. But that’s the origin of the argument as I understand it. And, to intentionally lean into the double negative, it’s “not unconvincing.”

So, based on this physiological rationale, it’s easy to see how “bring back the tallow fries” could be a compelling argument. Better taste, fewer carcinogens. Win-win?

KISS: “Keep It Saturated Stupid”

Now, we need to extend the logic: If seed oils, plant fats, and omega-6 are fragile, prone to oxidation, and generate harmful carcinogenic products, they’re “bad.” Right? “The elites have misled us and, as it turns out, animal fats like tallow are the health food, whereas omega-6 are unhealthy and to be avoided at all costs.”

As you hopefully can tell, I’m being hyperbolic.

But this is what a large mass of people believe. In fact, many of you reading right now might hold this perspective and be offended – prepared to stop reading – because you can tell I’m setting myself up to dismiss your point of view. But hang with me until we reach our destination…

There will be a few plot twists along the way.

Meta-Analyses Shows Higher PUFA Results in Better Heart Health Outcomes

If it’s not already clear, I don’t share the perspective that omega-6 and linoleic acid are outright “bad” for human health. The data do not support that claim, at least not consistently. Let me give you some examples.

In one meta-analysis of 30 studies looking for associations between linoleic acid levels in the blood and different tissues (like adipose [fat] tissue) and heart disease risk, researchers found an inverse association whereby higher levels of linoleic acid were associated with lower heart disease risk.

In particular, higher linoleic acid levels in the blood and in fat tissue were associated with lower risks of cardiovascular disease and cardiovascular disease-related death.

The relationship size was sizable as well, with a ~34-40% reduced risk of cardiovascular disease-related death when linoleic acid levels in fat were proportionally higher in the blood plasma or fat.

In another meta-analysis of randomized controlled trials, replacing PUFA for saturated fats was found to reduce risk of coronary heart disease by ~10% for each 5% increase in energy intake from PUFA.

So yes—according to these data—your arteries might like walnuts more than Twitter does. (Although we will have more to say on these meta-analyses below… prepare for a plot twist...)

Beginning to Resolve the Confusion

If you haven’t taken a moment to pause and try to reconcile the apparent discrepancy between the two lines of evidence, please do so now.

To remind you of the opposing points of view, here they are:

• Anti “Seed Oil”: Omega-6, like linoleic acid, are fragile, prone to oxidation, and can form toxic byproducts that promote inflammation and chronic disease

• Pro “Seed Oil”: A large body of human evidence, including observational and randomized controlled trial data, suggests increasing PUFA intake is associated with and/or results in better cardiovascular disease outcomes.

Question: Who is right?

Answer: Both and neither.

The discrepancy can be resolved by considering several contextual factors, three of which we will discuss now.

1. Not “Just” Omega-6. Seeing the data through the lens of Omega-3

In human dietary trials, it’s common for multiple variables to change at once. Perhaps of chief importance among these is omega-3 fatty acid intake. Omega-3 fats are generally anti-inflammatory and accepted as beneficial for cardiovascular health, brain health, and overall metabolic health.

In a rather ingenious meta-analysis, researchers partitioned studies based on whether the intervention included an increase in omega-3 and omega-6 fats, or omega-6 fats alone. Bear in mind many studies and meta-analyses have included trials where both omega-3 and omega-6 fat intakes were altered, but the conclusions were focused on omega-6.

What did the researchers find?

For the combined outcomes of heart attack and coronary heart disease-related death:

• In studies in which there was an increase in omega-3 intake, as well as omega-6 intake, There was a statistically significant 22% risk reduction (green diamond).

• By contrast, in trials including a specific increase of omega-6, there was a trending 13% increase in risk of heart attack and heart disease-related death (red diamond).

The authors of this meta-analysis concluded:

“[A]dvice to specifically increase n-6 PUFA intake, based on mixed n-3/n-6 RCT data, is unlikely to provide the intended benefits, and may increase the risks of CHD and death.”

Oslo Diet Heart Study (ODHS): Sardines vs Seed Oils?

As one specific example, in the Oslo Diet Heart Study (ODHS), “experimental dieters were instructed to substitute fish, shellfish and ‘whale beef’ for meats and eggs, and were actually supplied with considerable quantities of Norwegian sardines canned in cod liver oil… For context, this is equivalent to more than sixteen typical fish oil pills.”

But it gets worse…

In the two decades before the Oslo study, Oslo males exhibited a 7-fold increased incidence of first heart attack, coinciding with the pervasive use of partially hydrogenated oils and margarines.

This meant the control group consumed more margarines rich in trans fats, whereas “margarines were ‘entirely restricted’ and replaced with non-hydrogenated oils in the experimental group.”

In summary, the ODHS was not simply an omega-6 study, but one in which trans fats were also restricted and omega-3 intake was massively increased.

This pattern – whereby studies with multiple dietary modifications between the experimental and control groups are coded as “omega-6” studies – muddies the data waters.

What you see below is the graph from the meta-analysis we discussed earlier where “reduced risk of coronary heart disease by ~10% for each 5% increase in energy intake from PUFA.” Boxed in pink are the studies where omega-3 intake was changed as well. So, as you can see, the story is evolving…

In the rest of the letter, we discuss:

• Metabolic effects of Whole Foods vs Processed Oils

• Why You Are NOT What You Eat

• No Double Standards: In Defense of Tallow Too

• A Way Forward: Scientific Duty and Public Messaging

• Practical Takeaways and What To Eat (or Not Eat)