Wheat Series Part 2: Wheat and Gluten’s Effect on Intestinal Permeability

It was a comment I’d heard too many times. I was watching tennis with a friend who knew me as a cyclist, not as someone who researches nutrition. The commentators were discussing world number-one ranked tennis player Novak Djokovic’s newfound success since going on a gluten-free diet. My friend got noticeably irritated and finally blurted, “I’m tired of this gluten-free fad! There’s not a scrap of evidence it makes a difference unless you have celiac disease.”

As much as I wanted to, I chose not to respond, but thought to myself, The bottom drawer of my research cabinet is awfully heavy for not having a scrap of anything in it. This viewpoint that the health benefits of a gluten-free diet are more fad than science is a pervasive one. But what has led so many—including doctors and scientists—to say the research doesn’t exist?

Certainly the science is extensive for celiac disease where the role of gluten is indisputable. Gliadin, a protein in gluten, binds to a molecule in our bodies called tissue transglutaminase. In celiac patients it’s this new, combined molecule that sets off the inappropriate immune response.^{1, 2, 3} Without gluten, celiac disease couldn’t exist.

Recently other gluten-related disorders like gluten allergies and gluten ataxia have been identified.^{4, 5} But admittedly, these conditions affect only about 2-10% of the population. Outside of these diseases my friend has a point: research showing gluten having a direct pathogenic role, as it does in celiac disease, isn’t there.

But perhaps this is where the disconnect exists.

While a great deal of published research is showing that wheat and gluten can promote a large range of chronic conditions,^{4, 6, 7, 8} gluten’s role is not so direct. Instead, gluten may break down the body’s natural defenses, setting up an inflammatory environment. This environment is highly conducive to a variety of chronic diseases in those of us who are unfortunate enough to have the wrong genetics.^{9, 10}

Gluten is just one of the ways in which wheat can set the stage for unwanted inflammation and disease. Let’s start with a surprising function that came out of celiac research.

Zonulin and Its Triggers

One of the most important roles of our gut, beside processing nutrients and hosting rich microflora, is to provide a barrier blocking the entry of unwanted particles into the bloodstream. Fortunately tight junctions (TJ) between the epithelial cells of our intestine carefully regulate entry of all but a few small molecules and essential nutrients.

Over the last 20 years, Dr. Alessio Fasano at the University of Maryland has researched breakdowns in this barrier, ultimately identifying a molecule produced in the gut called zonulin.¹⁴ Zonulin has the unique ability to dissolve the occludins, claudins, zonular occluden, and ZO-1 proteins that make up the structural cytoskeletons of our tight junctions.^{6, 15, 16, 17, 18}

Put simply, zonulin can breakdown our intestinal barrier and increase permeability. An effect that’s often referred to around the web as “leaky gut.” It is rapid, reproducible, and—fortunately—reversible.¹⁶

To date, two powerful triggers for zonulin have been identified. The first trigger is exposure to bacteria in the intestine. Interestingly, infection by both pathogenic and “healthy” bacteria can have a triggering effect. However, it’s amplified with the “bad guys” as we can see from the chart below.¹⁹

It is believed that zonulin evolved to protect us against bacterial colonization in the gut.^{6, 17, 19} When there’s an overload of bacteria in an otherwise healthy digestive tract, zonulin opens up the tight junctions allowing fluid to rush into the gut and flush out microorganisms.

The second powerful activator of the zonulin system is gliadin. Gliadin fragments bind to the CXCR3 receptor on the epithelial cells of the gut. Then through a MyD88 signaling process, these epithelial cells release zonulin and cause an opening of tight junctions.^{6, 15, 17, 20, 21}

It’s a complex process, but all you need to know is that gliadin can do this from inside the gut. It doesn’t have to get into our systems. More importantly, gluten is inappropriately hijacking a powerful defense mechanism designed to handle bacterial contamination.¹⁷

In the above figure, we can see from Dr. Fasano’s research how gliadin’s ability to stimulate zonulin can be as powerful as bacterial triggers.⁶

Finally, while gliadin’s effect is much stronger in individuals with celiac disease, gliadin does not discriminate, and it happens in all people’s guts.^{6, 17}

Consequences of Intestinal Permeability

With a healthy gut barrier, large molecules are degraded before entering the body and are well tolerated by the immune system.¹² Intestinal permeability caused by gluten and bacteria allows these large molecules to get into circulation and act as antigens (activators) for the immune system.^15, 17, 22

This becomes a real concern considering gluten is normally consumed with a meal. Its rapid effect on gut permeability happens at the same time that the gut is being hit by a large number of foreign antigens.

Dr. Fasano and his group proposed that once these antigens gain entry, they can be misinterpreted by the immune system in genetically susceptible individuals. The result is an inappropriate immune response that ultimately leads to chronic illness.^{6, 12, 15, 23, 24, 25} In a healthy gut, these antigens would never gain access to the immune system.

The image below provides a representation of how gluten can open tight junctions and lead to diseases such as celiac disease and type 1 diabetes.⁶

Losing the Barrier to Disease

So, what does this all amount to? Intestinal permeability caused by either bacterial overgrowth or gluten (both of which are heavily influenced by diet) may be a key early step to set the body up for many chronic illnesses.

But is there any research? Fortunately, this is where I have to start using more drawers in my research cabinet.

Higher zonulin levels and intestinal permeability have been associated with and often precede many autoimmune conditions including celiac disease,^{17, 28, 34} multiple sclerosis,^{35, 36} rheumatoid arthritis,^{37, 38} ankylosing spondylitis,^{37, 39} and Crohn’s disease.^{40, 41} Eating wheat has been directly linked to diabetes.^{16, 30, 31, 32, 33, 42, 43, 44}

A popular theory of autoimmune disease called the molecular mimicry theory proposed that autoimmune disease is initiated by viruses that mimic our bodies.^{26, 27} Dr. Fasano and his group suggested instead that dietary antigens passing through a leaky gut may be the environmental trigger. To test their theory, they were able to use a zonulin inhibitor to reduce the severity of celiac disease symptoms in humans²⁸ and the incidence of type 1 diabetes in mice.²⁹

Intestinal permeability isn’t just associated with autoimmune conditions. Permeability may affect asthmatics by increasing their exposure to allergens.^{45, 46} Elevated zonulin levels have been found in irritable bowel disease ^{47, 48} and cancer.^{49, 50} Even schizophrenia has recently been linked to gluten consumption and zonulin levels.^{51, 52} But a final question remains.

In a world where most people reach for a bagel and toast as soon as they get out of bed, intestinal permeability may just be a part of Western life that gets an unfair rap by association. In other words, is it too easy to just link permeability with chronic disease? Does it really play a role?

In his 2011 review of zonulin and disease, Dr. Fasano addressed this question, pointing out a number of studies where symptoms and incidence rates were reduced when gluten was removed from the diet or when zonulin’s effects were blocked.⁶ Wheat, a no-no for any good Paleo dieter, was clearly opening doors.

Explore the rest of our Wheat Series:

Part 1: The Digestive Immune System

NEXT: How Wheat Mimics Bacteria

Part 4: Wheat as a Harmful Dietary Antigen

Part 5: How Wheat Can Trigger Chronic Disease

References

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