Thread by @ck_eternity_

There's a lot of debate on PUFA, so I decided to dive into the research with an open mind and see if I can clarify a few things

In this thread I'll be looking at human data on PUFA and inflammation, oil oxidation timelines, and my own views on the subject

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First off, many claim that both omega-3 and omega-6 fats are inherently inflammatory for a few different reasons

The most common explanations for this are that the oils are oxidized outside the body, that the oils oxidize in the body, and that they cause inflammation unoxidized

This meta-analysis looks at whether the omega-6 fats are inherently inflammatory in humans

They found that increasing dietary omega-6 does not increase inflammatory markers, and in fact many sources of these fats are anti-inflammatory
pubmed.ncbi.nlm.nih.gov/29610056/

However, the above study also noted that high intake of omega-6 fats may limit some of the anti-inflammatory effects of omega-3 fats

This seems to suggest that if there is any "inflammatory" effect, it either stems from a skewed O3:O6 ratio, or from a lack of omega-3 fats

This study looked at the inflammatory marker TNF-a in response to different PUFA-containing oils (olive, soy, cod liver, corn), and also found that most were anti-inflammatory

Oddly, corn oil was the one that showed only a neutral effect
pubmed.ncbi.nlm.nih.gov/21326271/

This study looked at the same oils in the context of endothelial function, oxidative stress, and inflammation

They also found no negative effect on either oxidative stress or inflammation, suggesting that these oils are not inherently oxidative either
pubmed.ncbi.nlm.nih.gov/19703325/

Now I will note the previous two studies administered the oils cold, so this does not cover the effects of consuming pre-oxidized oils

That said, it seems that just the fats themselves are not inflammatory or oxidized enough in the body to significantly increase oxidative stress

Now let's tackle the issue of pre-oxidized oils

This study looked at the consumption of oxidized omega-3 fats in rodents and tracked the levels of the oxidation by-product 4-HHE in the bloodstream
pubmed.ncbi.nlm.nih.gov/22865918/

They found that levels of 4-HHE in the bloodstream increased with dietary consumption, suggesting that the oxidation products are bioavailable in mammals

Since this is a rodent study though, we cannot draw good conclusions about inflammation in humans from it

So do we have the relevant human data?

Well, this meta-analysis looks at the effects of fish oil consumption in humans and found a broadly anti-inflammatory effect, but it's unclear if they checked the oxidation status of the oils in each study
pubmed.ncbi.nlm.nih.gov/25676565/

Meanwhile, this study actually compared oxidized vs. unoxidized fish oil, and its effects on inflammation and oxidative stress in human subjects

They found that neither oxidized or unoxidized fish oil increased markers of inflammation or oxidative stress!
pubmed.ncbi.nlm.nih.gov/22136711/

This might suggest that omega-3 oxidation doesn't really matter, but I found another study that suggests there is at least some difference

They compared the effects of oxidized fish oil, unoxidized fish oil, and high oleic sunflower oil, on cholesterol
pubmed.ncbi.nlm.nih.gov/28558855/

They found that oxidized fish oil actually increased LDL cholesterol by 19%, while unoxidized fish oil actually decreased it by 6%

If this is able to be replicated, then oxidation of fish oil may explain the discrepancy between many of the studies on omega-3 and heart disease!

So even if we assume any added inflammation from oxidized fish oil is negligible in most individuals, it should still be avoided for good measure due to potential negative effects on heart disease markers

This is also just based on 2 RCTs so far, so take it with a grain of salt

Based on a large number of studies such as these, about 30-40% of fish oil supplements sold are oxidized beyond legal limits

For this reason, I'd always go with whole seafood whenever possible
pubmed.ncbi.nlm.nih.gov/26688721/
pubmed.ncbi.nlm.nih.gov/30626234/
pubmed.ncbi.nlm.nih.gov/23255124/

But that's fish oil, I'm sure many of you are wondering about the same issues in the context of seed oil

While we've already established that omega-6 fats are not inherently inflammatory, I was unable to find any studies comparing the effects of oxidized vs. unoxidized seed oil

So in this case let's look at how oxidized seed oil actually is, both before and after cooking, as well as how long it takes to oxidize at normal cooking temperatures

After that, I'll wrap this up by giving you my thoughts on whether seed oil oxidation matters

It is often claimed that the heat used during the processing of seed oils is enough to oxidize them significantly

This study compared the oxidation of various fish oil supplements vs. different plant-derived food oils
ncbi.nlm.nih.gov/pmc/articles/P…

Surprisingly they found that the plant oils were significantly less oxidized on average than the fish oils, and that some of the least oxidized oils were actually seed-derived

This shows that oxidation in good quality plant oils is not generally cause for concern

There may be some outlier in the case oils that are stored poorly for long periods of time, or from manufacturers that lack proper quality control

For the most part though if there is an issue with oxidation it seems it would stem more from cooking temperature than manufacturing

So let's look at how long it takes for oxidation to occur during cooking

This study is a nice overview of this, looking at a wide variety of food oils
link.springer.com/article/10.100…

It uses two methods to assess oxidation rate for different oils:

The first, known as the Rancimat method, uses a combination of heating at 220 degrees F and oxygenation to age the oil at an accelerated rate, to assess the point where significant oxidation occurs

The second, known as the PDSC method, uses a combination of heating at 250 degrees F and pressurization to assess the first detectable onset of oxidation

Using method 1 they found that the shortest time it took for significant oxidation to occur with any oil was 3.6 hours, with some taking more than 35 hours

Using method 2, it was found that no oxidation occurred until after at least 15 minutes, with some taking more than an hour

Most other studies I found showed similar results

This seems to indicate is that seed oil oxidation tendency is frequently overestimated, though it should still be considered that higher cooking temperatures may shorten these times somewhat

I'll give you all my thoughts to summarize:

First, I see no reason not to choose the best quality plant oils possible

Most of the studies I've presented here used cold-pressed oils, so it's possible that solvent extracted may have oxidation levels more comparable to fish oil

Second, many in the health community will overhype the oxidation of seed oils to the point that you have people afraid of eating processed food on the off chance that the 0.5g of oil in it is oxidized

While avoiding these foods is good, there are more logical reasons to do so

Third, while the research points to no harm being caused by unoxidized PUFA even in the omega-6 form, I do believe there is a scenario where PUFA can become harmful

That scenario is fried restaurant food

Frying in restaurants usually uses the same oil for at least a week straight, which (given the oxidation times above) essentially guarantees significant degradation of the oil

When you compare this to cooking at home, it is a massive difference

The fact is that all the studies I've ever seen showing benefits from plant oils either used unheated or minimally heated oils

As far as I'm aware no study exists that compares fried food consumption where the oil is heated for days straight with 10-20 minutes at home cooking

When I consume fried food, even with no other potentially inflammatory added ingredients, I FEEL the inflammation within an hour after the fact

I've gone from being perfectly mentally healthy to borderline suicidal after consuming only one meal with oxidized oil

While this is an extreme example, this is enough personal experience for me to believe that fried food causes these issues

I am very in touch with my body, and have never felt any similar issue from fish oil supplements, or any type of plant oils heated briefly at home

Lastly, just because they're not inherently inflammatory, I still wouldn't consume soy, canola, or vegetable oil personally, simply because there are more nutritious options like olive, sunflower seed, or black cumin seed oil

If you can get even a minor added benefit, why not?

This ended up running a bit longer than expected, but I hope it clarified some of the nuance surrounding this topic, or at the very least made you think

To everyone that made it to the end, thanks for reading ❤️

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