Omega-6 Fatty Acids, Leaky Gut and Food Reactions: What New Research Shows
There is one conversation I seem to have with almost every new client: “healthy” fats and Omega 6:3 fatty acid balance.
And most people are pretty confident they're doing well.
They eat nuts and seeds. Maybe chia or flax. Nut butters. Olive oil. Avocado. They may avoid processed foods completely and cook nearly everything from scratch.
Then I ask another question: How often do you actually eat foods that provide EPA and DHA?
While most people are getting plenty of omega-6 fatty acids, relatively few of the people I work with regularly eat sardines, herring, mackerel, trout or other good sources of the long-chain omega-3 fatty acids EPA and DHA.
But aren't flax, chia and walnuts high in omega-3?
Kind of...
Plant foods such as flaxseeds, chia seeds, hemp seeds and walnuts contain an omega-3 fatty acid called ALA (alpha-linolenic acid). ALA is beneficial and essential, but it isn't the same as the long-chain omega-3 fatty acids EPA and DHA that we get primarily from oily fish and marine sources.
Before your body can use plant-based ALA as EPA or DHA, it has to convert it.
And that conversion isn't particularly efficient.
Only a relatively small proportion of ALA is converted into EPA, and conversion into DHA is even more limited. How efficiently this happens can also vary between individuals.
So while I absolutely recommend foods like flax, chia and walnuts - they provide fiber, minerals, polyphenols and many other beneficial compounds - I don't count them as equivalent to a direct source of EPA and DHA.
This is an important distinction because someone can be eating chia pudding every morning, adding flaxseed to their smoothie and snacking on walnuts and quite reasonably think:
“I'm getting plenty of omega-3.”
They're getting plenty of ALA.
That doesn't necessarily mean they're getting plenty of EPA and DHA.
The same applies to supplements. Some plant-based omega-3 supplements contain primarily ALA, while algae-derived omega-3 supplements can provide EPA and/or DHA directly. So if you don't eat fish, check the label: don't just look for the words omega-3 - look at how much EPA and DHA the product actually provides.
And when people do tell me they're eating oily fish, the answer is very often: “I eat salmon.”
But not all salmon is nutritionally identical
Here in Europe, the fresh Atlantic salmon available in most supermarkets is always farmed. Wild salmon is much harder to find fresh and either canned or frozen.
There is an important piece of the story that rarely makes it into the “eat more salmon” advice:
The fatty-acid composition of a fish is influenced by what that fish eats and how much it moves.
As aquaculture has expanded, the composition of salmon feed has changed substantially. Modern farmed-salmon diets contain plant-derived oils as well as marine ingredients. The fish don’t have much room to move and are raised to be quickly ready to eat. So that farmed salmon you may be buying is actually an obese teenager with bad skin that sits in front of a screen and eats junk food all day.
This kind of salmon provides mainly inflammatory Omega 6 fatty acids.
So rather than relying on salmon as our default answer to omega-3, I encourage clients to think more broadly.
Small oily fish such as sardines, herring and mackerel can be excellent sources of EPA and DHA.
Trout can be another useful option and is much more locally available in many parts of Europe.
And there is another reason I like dietary variety when it comes to fish: contaminant exposure differs enormously between species.
Mercury and other toxins accumulate particularly in large predatory fish. Tuna, for example, can contribute considerably more methylmercury than smaller oily fish. That's why European food-safety authorities recommend varying the species we eat rather than relying heavily on large predatory fish (generally avoid tuna, swordfish, shark, ray and of course pangasius).
What does your overall fatty-acid balance actually look like?
Even someone eating a beautiful whole-food diet can end up consuming plenty of omega-6 fatty acids while getting surprisingly little EPA and DHA.
And until recently, we mostly discussed this balance in relation to things such as cardiovascular health and inflammation.
But new research published in 2025 has added another fascinating piece to the puzzle.
It suggests that the balance between omega-6 and omega-3 fatty acids may also influence the microscopic structures responsible for keeping the intestinal barrier intact.
In other words: Our fatty-acid balance may have something to do with what we commonly call “leaky gut.”
And that could change the way we think about food reactions too.
New research: fatty-acid balance may affect your intestinal barrier
A study published in Food Bioscience in April 2025 specifically investigated what happens to an intestinal barrier model when researchers change the ratio between omega-6 and omega-3 fatty acids.
They compared ratios of:
1:1
5:1
and
15:1 omega-6 to omega-3.
The differences were striking: At the high 15:1 ratio, researchers observed increased oxidative stress.
They also saw activation of an inflammatory pathway called TLR4/NF-κB, accompanied by increased inflammatory signals including IL-6 and TNF-alpha.
But here's the finding that particularly caught my attention: The high omega-6 environment also disrupted the expression of tight-junction proteins and compromised the integrity of the intestinal barrier model.
Why does that matter?
Because tight junctions are essentially the microscopic “gates” connecting the cells lining your intestine.
And their job is incredibly important.
Your gut barrier is held together by tiny “gates”
The cells lining your intestine aren't simply sitting next to each other.
They're connected by structures known as tight junctions.
You can imagine them as microscopic gates between intestinal cells. Proteins including occludin, claudins and ZO-1 help regulate what is allowed to pass from the intestine into the body.
We want this barrier to be selective: nutrients need to get through.
But bacteria, bacterial products and other substances generally shouldn't have free access to the bloodstream.
When the regulation of these tight junctions becomes disrupted, intestinal permeability can increase. This is also when food sensitivities occur: the proteins in our food are “leaking” through the gut barrier into our blood stream and are falsely activating our immune system that starts reacting as it considers them as invaders.
This is what most people mean when they use the term “leaky gut.”
And this is where fatty acids become particularly interesting.
In other words, the fatty-acid environment influenced the machinery responsible for keeping the intestinal barrier intact.
Now, this is important:
This was experimental cell research, not a clinical trial showing that eating too many almonds gives humans leaky gut.
But it provides a biological mechanism that helps us understand something we've suspected for a long time:
The intestinal barrier doesn't exist independently from the inflammatory and nutritional environment surrounding it.
And oxidation may matter too
There's another piece of the puzzle that I find particularly interesting.
Polyunsaturated fats are, by their chemical nature, relatively vulnerable to oxidation.
Research using intestinal cells has found that oxidized linoleic acid can increase reactive oxygen species and interfere with tight-junction function while damaging the intestinal-cell layer.
That doesn't mean linoleic acid itself is inherently harmful.
It tells us that what happens to a fatty acid matters too.
Its source matters.
Its metabolic environment matters.
Oxidative stress matters.
And the overall fatty-acid environment matters.
We thought that food sensitivities are always linked to “leaky gut”
For years, the functional-medicine explanation for developing multiple food sensitivities has often gone something like this: Gut barrier becomes permeable → food proteins encounter the immune system → immune system reacts → food sensitivities develop.
And this is still valid - however, we need to recognize now that it isn't the only pathway.
Fatty acids don't just become part of cell membranes.
They also participate in immune signaling.
And some fascinating new research illustrates this.
A 2026 study investigated linoleic acid in mice with cow's-milk-protein allergy.
Researchers found higher levels of linoleic acid within a type of immune cell called group 2 innate lymphoid cells, or ILC2s, in the allergic mice.
ILC2s are involved in type-2 immune responses - the kind of immune environment associated with allergic disease.
The researchers found evidence that linoleic acid could activate the NF-κB pathway and promote the release of inflammatory signaling molecules including IL-5 and IL-13, worsening the allergic response.
Again, these were mice.
This research does not demonstrate that eating omega-6 foods causes food allergies in humans. But it raises a fascinating possibility.
Fatty-acid balance may influence food reactivity not only by affecting the intestinal barrier, but also by influencing the immune environment itself.
And that changes the way I think we need to talk about food reactions.
A food reaction doesn't tell us why you reacted
This may be the most important takeaway from this entire article:
Reacting to a food does not automatically mean you're “sensitive” to that food.
And it doesn't automatically mean you have leaky gut.
A reaction might involve intestinal permeability and immune exposure.
But it might also involve:
histamine or mast-cell activation
a genuine IgE-mediated allergy
fermentation or poor digestion of particular carbohydrates
microbiome changes
inflammatory immune signaling
altered fatty-acid metabolism
or several of these mechanisms happening at the same time
This is particularly important when someone seems to react to more and more foods.
The natural response is often to keep eliminating them.
Dairy goes.
Then gluten.
Then eggs.
Then nuts.
Then pulses.
Eventually, someone is eating five “safe” foods and is terrified to introduce anything else.
At that point, I become much more interested in the question: Why has this person's system become so reactive?
What about omega-3?
This is where I come back to the conversation I have with so many clients.
Eating chia seeds, flaxseed and walnuts is great.
Please don't stop eating them because you read this article.
They provide fiber, minerals, polyphenols and an omega-3 fatty acid called ALA, or alpha-linolenic acid.
But ALA isn't the same thing as EPA and DHA.
Your body can convert ALA into the longer-chain omega-3s, but that conversion is limited and varies considerably between individuals.
That means a spoonful of flaxseed shouldn't necessarily be considered nutritionally equivalent to eating oily fish.
EPA and DHA are found primarily in marine foods, particularly fatty fish.
And this is also where we need to make an important distinction with vegan omega-3 supplements.
Many plant-based “omega-3” products provide ALA.
Others are made from microalgae and provide DHA and, increasingly, EPA directly.
Those are not the same product.
In fact, algae are ultimately where the marine food chain gets these long-chain omega-3 fatty acids in the first place.
So if you don't eat fish, look at the actual label rather than simply looking for the words vegan omega-3.
Ask yourself: Does this contain ALA, or does it actually provide EPA and DHA?
EPA isn't simply an “anti-inflammatory pill”
You'll often hear EPA described as anti-inflammatory.
That's useful shorthand, but again, the biology is more sophisticated.
EPA and DHA can be used to produce families of lipid mediators involved not only in regulating inflammatory responses but also in helping resolve inflammation.
Resolution is important.
A healthy inflammatory response isn't about never producing inflammation. We need inflammation to fight infection, repair injuries and respond appropriately to threats.
The problem is when the body becomes very good at switching inflammation on and not particularly good at switching it off.
That distinction becomes especially relevant in people whose systems seem chronically reactive.
So should you stop eating nuts and seeds?
No.
That's not the message I want you to take away.
Whole nuts and seeds bring plenty of benefits and are very different nutritionally from a diet dominated by ultra-processed foods and repeatedly heated or oxidized oils.
Instead, take a step back and look at your overall pattern.
You might ask yourself: How often am I actually eating EPA- and DHA-rich foods?
For people who eat fish, that could mean intentionally including oily fish such as sardines, salmon, herring or mackerel regularly.
If you don't eat fish, consider whether your omega-3 supplement actually contains EPA and DHA, rather than assuming that every product labeled “omega-3” provides them.
At the same time, build the rest of the environment that supports your intestinal barrier:
Eat a diverse range of plants.
Feed your microbiome the fibers it uses to make beneficial short-chain fatty acids.
Include colorful polyphenol-rich foods.
Prioritize minimally processed fats and foods.
And don't forget that sleep, stress, alcohol, medications, hormones and the microbiome can all influence the intestinal environment too.
The bigger picture
What I love about this newer research is that it gives us another example of something I see again and again:
The body doesn't work in isolated systems.
The fats you eat don't simply get stored as body fat.
They become part of cell membranes.
They influence signaling molecules.
They interact with your microbiome.
They participate in immune regulation.
And emerging research suggests that the balance and metabolism of these fatty acids may also influence the tight junctions helping to protect your intestinal barrier.
So when someone suddenly seems to react to everything they eat, my first question isn't:
“Which other foods should we remove?”
It's:
“What is making this system so reactive in the first place?”
Sometimes intestinal permeability may be part of that answer.
Sometimes histamine or mast cells may be involved.
Sometimes digestion or the microbiome may be contributing.
And fatty-acid balance may be another piece of that much larger puzzle.
Because when it comes to food reactions, the food itself isn't always the whole story.
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