Food Intolerance: Is the Food Really the Problem?

Don't just ask, “What food am I intolerant to?” Ask, “Why is my gut reacting to this food?”

Gluten.

Dairy.

Nuts.

Beans.

Onions.

Garlic.

Wheat.

For millions of people experiencing digestive problems, the solution seems increasingly obvious:

Find the offending food and remove it.

Then another food causes bloating, discomfort or diarrhoea.

So that goes too.

Then another.

Before long, somebody who once ate a wonderfully varied diet can find themselves surviving on an increasingly narrow collection of “safe” foods.

But what if, in some cases, we are asking the wrong question?

Instead of continually asking:

“What can't I eat?”

perhaps we should sometimes be asking:

“Why has my gut become less able to tolerate the foods I eat?”

That distinction could completely change the conversation around food intolerance.

First: intolerance is not the same as allergy

This distinction is extremely important.

Food intolerance is not one disease and it does not have one cause.

A genuine food allergy involves the immune system responding to particular food proteins and can potentially be life-threatening.

Coeliac disease is different again. It is an autoimmune condition in which gluten triggers an immune response that damages the small intestine in genetically susceptible people.

Lactose intolerance has another mechanism. It commonly results from insufficient lactase, the enzyme required to digest lactose.

And then there are people who experience bloating, abdominal discomfort, altered bowel habits or other symptoms after eating particular foods without having any of these conditions.

These differences matter.

Nobody with a diagnosed food allergy should attempt to “train” themselves to tolerate that allergen.

Someone with coeliac disease should not reintroduce gluten in an attempt to improve their microbiome.

But for the much larger conversation around digestive sensitivity and self-described food intolerance, there is another fascinating question:

Why can somebody comfortably eat a food for years and then apparently become unable to tolerate it?

Perhaps we need to look beyond the food itself.

Meet one of the most extraordinary organs in your body

Your digestive system isn't simply a pipe through which yesterday's dinner travels.

The intestinal surface is one of the largest and most biologically active interfaces between your body and the outside world.

Modern estimates put the gastrointestinal mucosal surface at approximately 30–40 square metres.

And separating the contents of your intestine from the tissues beneath is an epithelial barrier that is, remarkably, essentially one cell thick.

Those intestinal epithelial cells are also replaced extraordinarily quickly - typically over approximately 3–5 days.

Just think about that.

Around 30–40 square metres.

A barrier essentially one cell thick.

Continually renewing itself every few days.

Meanwhile, breakfast, lunch, dinner, drinks, medicines, food additives and trillions of microorganisms are interacting with the other side of it.

So perhaps your gut deserves a little selfish TLC.

Because looking after this extraordinary interface isn't merely about avoiding indigestion.

Your intestinal barrier has to perform an astonishing balancing act every day.

It must allow nutrients, water and other useful molecules to pass into the body while simultaneously maintaining a controlled boundary between us and the enormous microbial and chemical environment contained within the intestine.

Your gut isn't a wall - it's a highly controlled border

The cells forming the intestinal lining are connected by structures including tight junctions.

Think of them as part of an extraordinarily sophisticated border-control system.

They help regulate movement across the intestinal epithelium while the immune system continuously monitors what is happening around it.

When intestinal barrier regulation becomes disturbed, permeability can increase.

You will often hear this described as “leaky gut.”

The phrase is useful for explaining the concept, but the actual science is considerably more sophisticated.

Increased intestinal permeability is recognised in several gastrointestinal and inflammatory diseases. But it would be scientifically incorrect to claim that “leaky gut” causes every food intolerance or every inflammatory condition.

The relationship can work in several directions.

Inflammation can affect barrier integrity.

Changes in the microbiome can influence the intestinal environment.

Disease can alter permeability.

Diet can influence microbial metabolism.

And the intestinal immune system is constantly interacting with all of them.

The gut is an ecosystem, not a plumbing system.

And what about white blood cells?

There's another popular explanation worth correcting.

Food doesn't normally escape through holes in the intestine where white blood cells suddenly discover it floating around in the bloodstream.

White blood cells are already present throughout our circulation and within the enormous network of immune tissue associated with the intestine.

What can change is the interaction between the immune system and dietary or microbial molecules at the intestinal barrier.

When barrier function, microbial ecology or immune regulation becomes disturbed, exposure to these molecules can change and potentially contribute to immune activation and inflammation in susceptible individuals.

That is a much more accurate picture than simply saying:

“Food leaked through my gut and my immune system attacked it.”

Why does gluten cause so much confusion?

Few foods illustrate the problem better than gluten.

Someone eats bread and becomes bloated.

They stop eating bread.

The bloating improves.

The obvious conclusion is:

“I'm gluten intolerant.”

But that isn't necessarily what happened.

There are at least three important possibilities.

1. Coeliac disease

Coeliac disease is an autoimmune disease in genetically susceptible people.

Gluten peptides provoke an immune response that damages the lining of the small intestine. Increased intestinal permeability is also an important feature of coeliac disease.

Genetics therefore absolutely matters.

This is why anyone who suspects coeliac disease should seek appropriate medical testing rather than simply eliminating gluten indefinitely. Testing is generally most useful while gluten is still being consumed.

2. Wheat allergy

This is an allergic immune response to proteins found in wheat and is biologically different from coeliac disease.

3. Non-coeliac gluten/wheat sensitivity

This is more complicated.

People can experience genuine symptoms associated with eating wheat despite not having coeliac disease or a conventional wheat allergy.

And fascinatingly, gluten itself might not always be the only component involved.

Wheat also contains fermentable carbohydrates called fructans, part of the FODMAP family.

For some people, these carbohydrates can contribute to gas, distension, discomfort and altered bowel habits.

So removing bread can make someone feel dramatically better without necessarily proving that gluten itself was responsible.

The symptom is real. The assumed explanation isn't always correct.

What about nuts?

Another misconception is that hard fragments of nuts can physically penetrate a “leaky” intestinal wall.

That's not how intestinal permeability works.

Food undergoes extensive mechanical, chemical and enzymatic digestion before and during its passage through the intestine.

However, nuts can certainly cause problems for some people.

A genuine nut allergy can produce a serious immune reaction to specific proteins.

But nuts also contain fibre, fats and other compounds that can create digestive symptoms in susceptible individuals.

Those are very different mechanisms.

This distinction becomes particularly important when we start talking about fibre-rich foods.

Are we sometimes eliminating the foods our microbiome needs?

Beans cause gas.

Lentils cause bloating.

Onions cause discomfort.

Whole grains cause symptoms.

Certain fruits seem problematic.

So out they go.

And initially somebody may feel much better.

But there is an important question we rarely ask:

What happens to the microorganisms that were feeding upon those plant fibres?

Many dietary fibres and resistant carbohydrates escape digestion in the upper gastrointestinal tract and eventually reach the colon.

There they become substrates for our resident microorganisms.

Microbial fermentation can produce compounds including the short-chain fatty acids acetate, propionate and butyrate.

Butyrate is particularly interesting because cells lining the colon can use it as an important energy source, and it has important relationships with intestinal barrier and immune function.

So fermentation in the colon isn't necessarily something we should fear.

Gas is also a normal product of microbial fermentation.

Consequently:

Bloating does not automatically equal damage.

And:

Gas does not automatically mean a food is bad for you.

Dose matters.

Your existing microbiome matters.

Digestive capacity matters.

How quickly you changed your diet matters.

And the overall ecosystem matters.

The elimination trap

There are situations where elimination diets can be extremely useful.

A professionally supervised low-FODMAP diet, for example, can help identify dietary triggers in people with IBS.

But elimination should not automatically become permanent restriction.

Imagine someone regularly consumes 40 different plant foods.

Wheat causes symptoms.

Remove it.

Beans cause symptoms.

Remove them.

Onions and garlic cause symptoms.

Remove them.

Then nuts.

Then seeds.

Then certain vegetables.

Then particular fruits.

The diet becomes smaller and smaller.

The symptoms may initially improve because fewer fermentable substrates are reaching the colon.

But the microbiome has also lost access to an increasingly diverse range of substrates.

This leads to a fundamentally different philosophy of gut health.

Instead of asking:

“How many foods can I remove?”

perhaps the long-term ambition - where medically appropriate - should be:

“How much dietary diversity can I comfortably build?”

Restriction versus resilience

This is the distinction we think deserves much more discussion.

Modern nutrition can become obsessed with what we should remove.

Sugar-free.

Gluten-free.

Dairy-free.

Lectin-free.

Carbohydrate-free.

Low-FODMAP.

Low-histamine.

And sometimes there are perfectly legitimate medical reasons for doing exactly that.

But indiscriminate restriction isn't synonymous with gut health.

Our microbiome represents a vast ecological community.

Different microorganisms utilise different substrates.

Different plants provide different fibres, polyphenols and phytochemicals.

So rather than permanently shrinking the nutritional environment, perhaps we should think about how we can help support a gut ecosystem capable of dealing with greater diversity.

Not overnight.

Not by forcing foods that produce severe symptoms.

And certainly not by ignoring diagnosed medical conditions.

But gradually, intelligently and individually.

Food intolerance may sometimes be telling us something

Symptoms are information.

They're not necessarily a diagnosis.

Bloating after beans doesn't automatically mean you're intolerant to beans.

Discomfort after bread doesn't automatically diagnose gluten intolerance.

Gas after increasing fibre doesn't automatically mean fibre is damaging you.

The better question might be:

What is happening within the digestive environment when I eat this food?

That leads us towards a much broader investigation.

Digestive enzymes.

Gastrointestinal motility.

Microbial composition.

Fermentation.

Intestinal barrier function.

Immune regulation.

Previous infections.

Medication.

Antibiotic exposure.

Stress.

Sleep.

Exercise.

And perhaps most importantly:

the overall quality and diversity of the diet.

Your microbiome needs feeding too

We often talk about “taking probiotics”.

But that can overlook something fundamental.

Whatever microorganisms are living within our colon require substrates.

Much of that nutrition ultimately comes from the plant material we eat.

Vegetables.

Fruit.

Legumes.

Whole grains.

Nuts.

Seeds.

Herbs.

Spices.

Different plants contain different fibres and phytochemicals.

That is one reason why dietary diversity is so interesting in microbiome science.

Rather than obsessing over one supposed “superfood”, think ecosystem.

You don't create a rainforest by planting one species of tree.

So where do fermented foods fit?

Fermentation introduces another fascinating dimension.

Before fermented food ever reaches your mouth, microorganisms have already begun transforming its constituents.

Microbes metabolise carbohydrates and produce organic acids and numerous other fermentation-derived compounds. Depending upon the organisms, ingredients and fermentation conditions, fermentation can also transform phenolic compounds, proteins and many other components of food.

In other words:

Fermentation begins some of the biochemical transformation of food outside the body.

That does not mean fermented foods cure food intolerance.

They don't.

But it helps explain why fermented foods are attracting considerable scientific attention.

One particularly interesting Stanford intervention study published in Cell compared diets rich in fermented foods with diets rich in fibre. The fermented-food diet increased microbiota diversity and reduced several inflammatory markers during the study, although this was a relatively small intervention and should not be interpreted as proof that all fermented foods produce the same effects.

That distinction is important.

Not every ferment is the same.

The microorganisms matter.

The ingredients matter.

The fermentation conditions matter.

And the final biochemical composition matters.

This is where Tibico becomes interesting

At Tibico, our philosophy has always been remarkably simple:

Nature already contains extraordinary nutrition. Our job is not necessarily to add more - it is to unlock more.

Tibico uses whole fruits, roots, herbs and spices combined with our controlled fermentation process.

We're increasingly interested not simply in what goes into a ferment, but what microorganisms create and transform during fermentation.

That is why we are investing in scientific analysis.

We want to understand the microbial and biochemical composition of Tibico rather than simply making assumptions because it is fermented.

But there's another important principle.

Tibico isn't a substitute for a good diet.

If somebody drinks fermented nutrition every morning but spends the remainder of the day consuming a highly restricted, fibre-poor, ultra-processed diet, they're ignoring an enormous part of the gut-health equation.

We believe fermented foods and a diverse plant-rich diet belong together.

Plants provide substrates for the existing microbial ecosystem.

Fermentation brings another dimension of microbial transformation.

It isn't about one miracle ingredient.

It's about nurturing the ecosystem.

Give your gut some selfish TLC

We spend extraordinary amounts of time thinking about our skin.

We moisturise it.

Protect it from the sun.

Clean it.

Exfoliate it.

Buy expensive creams for it.

Yet hidden inside us is another enormous biological surface.

Around 30–40 square metres of gastrointestinal mucosa.

Much of the intestinal barrier consists of an epithelial layer just one cell thick.

And those epithelial cells are continuously being replaced, typically within only 3–5 days.

Think about the job we're asking that surface to perform.

Every day.

Every meal.

For perhaps eighty or ninety years.

Don't you think it deserves a little selfish TLC?

Feed it plants.

Feed the microorganisms that live within it.

Eat diversity.

Include fermented foods if you tolerate them.

Move your body.

Sleep.

Don't smoke.

Moderate alcohol.

And don't automatically interpret every digestive symptom as evidence that another whole food needs to disappear from your life forever.

Perhaps we've been asking the wrong question

Food intolerance has conditioned many people to approach nutrition from a position of fear:

What can't I eat?

Sometimes that question is medically essential.

But perhaps it shouldn't always be our first question.

Instead ask:

Why am I reacting to this food?

Has something changed within my digestive environment?

Could the quantity be the problem rather than the food itself?

Am I confusing microbial fermentation with damage?

Has my diet become progressively less diverse?

Could carefully rebuilding diversity improve my nutritional ecosystem?

And ultimately:

Instead of continually asking which foods your gut can't tolerate, ask what you can do to create a gut environment capable of tolerating greater dietary diversity.

That's a fundamentally different philosophy.

It moves us from restriction towards resilience.

From blaming individual foods towards understanding an ecosystem.

From endlessly removing things towards thinking about what our microorganisms actually need.

And from treating the gut as a simple digestive tube towards recognising it for what it really is:

One of the most extraordinary biological ecosystems in the human body.

Perhaps it's time we started looking after it accordingly.

Further reading & references

Helander HF, Fändriks L. (2014). Surface area of the digestive tract – revisited. Scandinavian Journal of Gastroenterology, 49(6), 681–689. Modern calculations put the total gastrointestinal mucosal surface at approximately 32 m², substantially below the older textbook “tennis court” estimate.

van der Flier LG, Clevers H. (2009). Stem Cells, Self-Renewal, and Differentiation in the Intestinal Epithelium. Annual Review of Physiology, 71, 241–260. A useful review of the extraordinary renewal of the single epithelial cell layer covering the intestine.

Rath E, Moschetta A, Haller D. (2018). Mitochondrial function - gatekeeper of intestinal epithelial cell homeostasis. Nature Reviews Gastroenterology & Hepatology, 15, 497–516. Reviews intestinal epithelial homeostasis and the rapid 3–5-day renewal cycle.

Wastyk HC et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137–4153.e14. A particularly interesting human dietary intervention examining high-fermented-food and high-fibre diets, microbiome diversity and immune markers.

Damianos JA, Bledsoe A, Camilleri M, Murray JA. (2026). Coeliac disease and the intestinal barrier: mechanisms of disruption and strategies for restoration. Gut. A very recent review examining gluten, immune responses, intestinal permeability and barrier function in coeliac disease.

Greger M, Stone G. (2025/2026). How Not to Die: Revised and Updated - Tenth Anniversary Edition. The extensively revised edition incorporates more recent nutrition and longevity research and continues Dr Michael Greger's examination of the relationship between whole plant foods, lifestyle and chronic disease. The revised US edition was published in December 2025, with the UK Tenth Anniversary Edition published by Pan Macmillan in 2026.

A final Gut School thought

Don't spend your life simply asking what you should remove from your diet.

Ask what you can add to help create a more diverse, resilient nutritional ecosystem.

Your gut is working for you 24 hours a day, seven days a week.

Maybe it's time to return the favour.

Tibico, unlocking nature with science.