What is gluten: everything you need to know if you have celiac disease

If you have just been diagnosed with celiac disease—or if you have been hearing about gluten for months and have never been sure what it really is—you are in the right place. Knowing what gluten is, which foods it appears in, and how it affects the body is the starting point for making informed decisions about what you eat.

What is gluten and what is it used for in food?

Gluten is a composite protein naturally present in certain cereals. It is not an additive invented by the industry: it has been there since the cereal itself existed. Its name comes from the Latin gluten, which means "glue," and that quite accurately describes its primary function both in home cooking and the food industry.

Gluten composition: gliadin and glutenin

Gluten is not a single protein. It is the union of two: gliadin and glutenin. When wheat flour is mixed with water and kneaded, these two proteins link up to form an elastic and extensible network. That network is what traps the carbon dioxide released by yeasts during fermentation. The result: a fluffy crumb, a crispy crust, bread that rises. Without that network, the dough crumbles.

Gliadin is the fraction that triggers the immune response in people with celiac disease. Specifically, one of its fragments—the 33-amino acid peptide known as 33-mer—is what a celiac's immune system identifies as a threat and attacks. A technical detail that has very practical consequences in everyday life.

Why the food industry uses it so much

Gluten is cheap, abundant, and technically very versatile. It provides elasticity to bread and pasta doughs, acts as a thickener in sauces and soups, and improves the texture in processed meat products like sausages or deli meats. It also helps coatings stick better to fried foods. That is why it ends up appearing in places where no one would look for it.

Which foods contain gluten

The most practical question any newly diagnosed person asks is exactly this. And the answer has two layers: the cereals that contain it naturally and the processed products where it slips in as a secondary ingredient—sometimes with its own name on the label, sometimes almost hidden.

Cereals that contain it naturally

The four major gluten-containing cereals are wheat, barley, rye, and spelt. Oats deserve a separate mention: they do not naturally contain gluten, but in Spain, almost all oats on the market are contaminated during cultivation or processing. Our recommendation is to avoid them unless the packaging explicitly specifies that they are certified gluten-free oats.

Cereal	Contains gluten	Observations
Wheat (and its varieties: spelt, kamut, einkorn)	Yes	The most widespread in bakery and pastry products
Barley	Yes	Present in beers and some malt products
Rye	Yes	Common in dark breads and sliced bread
Oats	No (but risk of contamination)	Only consume with gluten-free certification
Rice, corn, quinoa, millet	No	Safe for celiacs in pure form

How gluten affects you when it is present in processed foods

The problem with products that contain gluten is not just that they are made with wheat. It is that gluten can appear as a hidden ingredient in dozens of processed products where no one would look for it: a packet soup, soy sauce, corn snacks manufactured in facilities that also work with wheat flour. Cross-contamination during the manufacturing process is enough to cause a reaction in a celiac person.

Which products contain gluten without you expecting it

This is, probably, the most useful part of the entire article. And here we want to be direct: our recommendation is to be suspicious of any processed product until you have read the full label. It is not a paranoid attitude. It is a safety habit that, once incorporated, becomes automatic.

Some examples that still surprise even people with years of experience managing the diet:

• Sausages and deli meats: many use wheat starch as a binder. Low-quality cooked ham is one of the most common and least known cases.
• Commercial sauces: traditional soy sauce, Worcestershire sauce, and some industrial ketchups contain wheat in their formulation.
• Bouillon and soup cubes: wheat starch appears almost systematically among the ingredients.
• Malt beverages: conventional beer is made with malted barley. Gluten-free beer exists, but you have to look for it specifically and verify the certification.
• Medications and supplements: some tablets use wheat starch as an excipient. Always consult the package insert or ask your pharmacist directly.
• Potato chips: the problem is not the potato itself, but the factory. Many brands process on lines shared with wheat products.

How to read labels to detect gluten

European regulations require highlighting the 14 main allergens—including gluten—in the list of ingredients, usually in bold or underlined. But there are two situations where labeling does not fully protect you. The first: when the product is sold in bulk or in catering establishments, where the obligation to inform exists but is not always strictly followed. The second: when cross-contamination occurs in the factory and the manufacturer only includes the generic warning "may contain traces of gluten."

For a celiac person, "may contain traces" is not a cosmetic warning. It is a real alert signal. Always look for the crossed-out grain symbol or certification from recognized organizations such as the Celiac Association of Catalonia or FACE.

How gluten affects the body depending on your situation

Not everyone reacts to gluten in the same way. There are three distinct clinical situations, and confusing them generates more doubts than certainties. It is worth understanding each one separately.

What happens to the body when you eat gluten and you are celiac

Celiac disease is an autoimmune condition. When a celiac person ingests gluten, their immune system reacts by attacking the intestinal villi—the tiny structures that line the small intestine and allow for nutrient absorption. Over time, those villi flatten and the intestine loses its absorptive capacity. The consequences can range from classic digestive symptoms (bloating, diarrhea, abdominal pain) to manifestations that seem to have nothing to do with the intestine: anemia, chronic fatigue, dermatitis herpetiformis, fertility issues, or neurological impairment.

What makes diagnosis especially complicated is that approximately 20% of celiacs are asymptomatic at the digestive level. Intestinal damage occurs regardless, but it does not warn you with pain. That is why the only way to confirm celiac disease is through blood work with specific markers—anti-transglutaminase antibodies—and, if positive, an intestinal biopsy.

What happens if you have non-celiac gluten sensitivity

There is an intermediate group between confirmed celiacs and those who have no problem with gluten: people with non-celiac gluten sensitivity. They present similar symptoms—bloating, digestive discomfort, brain fog—but analytical markers for celiac disease are negative and there is no damage to the intestinal mucosa. Diagnosis is, by exclusion, complicated. And the treatment remains the same: remove gluten from the diet.

How do I know if I am gluten intolerant or celiac

If you have had vague digestive symptoms for a long time—frequent bloating, unexplained fatigue, anemia that does not respond to iron—talk to your doctor and request a specific blood test. The most common mistake is to remove gluten from the diet before getting tested. If you have been gluten-free for weeks or months, analytical markers can give false negatives and the diagnosis remains up in the air.

Can you remove it on your own and observe if you improve? Yes. But if you later need an official diagnosis, you will have to reintroduce gluten for several weeks before the blood test. Our recommendation is always the same: first the blood test, then the diet.

Is gluten bad even if you are not celiac?

The short answer is no. For most of the population, gluten is perfectly harmless. Gluten-free diets have become popular for reasons unrelated to health—marketing, wellness trends, the association with a "cleaner" diet—but there is no solid scientific evidence to justify eliminating gluten if there is no celiac disease or diagnosed sensitivity. In fact, doing so without planning can lead to deficiencies in fiber, iron, and B vitamins if the alternative diet is not well designed.

But this also deserves a nuance. If a non-celiac person decides to follow a gluten-free diet by choice and does so in a balanced way, there is no harm. The key is that this decision be an informed one—not that gluten is inherently harmful to everyone.

Living gluten-free without giving up pleasure

Here we want to be direct. Removing gluten from your diet should not mean giving up a fluffy croissant, a chocolate-covered donut, a birthday cake, or a crispy ciabatta. That is exactly what we have been solving at Jansana since 2015.

In our workshop, we use exclusively gluten-free flours and ingredients as a certified gluten-free company. There is no mixing of flours. There is no risk of cross-contamination. And since 2015, we have been accredited by the Celiac Association of Catalonia—a certification that is not obtained with declarations of intent, but with real process audits.

Our story began more than 90 years ago in Santa Perpètua de Mogoda. Decades working with sourdough, with long fermentation times, with the know-how of a neighborhood bakery. We have transferred all of that entirely to a 100% gluten-free production. If you have never tried a gluten-free croissant made in an artisan workshop, it is difficult to explain the difference in words. The crumb has body. You can taste the butter. The puff pastry crunches.

For those of you who cannot come to our store at Balmes 106 in Barcelona, we ship throughout Spain. Our recommendation is to freeze the products as soon as you receive them—directly in the original packaging—to preserve the texture like the first day. And if you want to go beyond bread, in our range of gluten-free pastries made daily you will find everything from ensaimadas to cinnamon rolls.

For special occasions, our artisan gluten-free apple pie or the Sara butter and almond cake are two options you would not distinguish from their gluten-containing equivalent in a conventional bakery. It is not an exaggeration: it is what our customers tell us in more than 400 reviews.

In our experience, the biggest obstacle for a celiac person to live normally is not the lack of information about gluten. It is the lack of really good options. That is why we make everything daily, in our own workshop, and with the accreditation that backs it up. If you want to see everything we make, check out our online store and place your first order.

Frequently asked questions about gluten

What is gluten and what is it used for?

Gluten is a composite protein—made of gliadin and glutenin—present in cereals such as wheat, barley, and rye. In cooking, it provides elasticity and fluffiness to doughs. In the food industry, it acts as a thickener and binder in sauces, sausages, and processed products.

Which foods contain gluten?

It appears naturally in wheat, barley, rye, and spelt. But it is also found as a hidden ingredient in sausages, soy sauces, bouillon cubes, conventional beer, and many processed products. Reading the full label is essential to detect it.

How do I know if I am gluten intolerant or celiac?

Diagnosis of celiac disease requires a blood test with specific markers—anti-transglutaminase antibodies—and, if positive, an intestinal biopsy. It is important not to remove gluten before the test, as it can alter the results. Non-celiac gluten sensitivity is diagnosed by exclusion, always under medical supervision.

Is gluten bad even if you are not celiac?

No. For the majority of the population, gluten is perfectly safe. Gluten-free diets are trendy, but there is no scientific evidence to justify eliminating it without a diagnosis. Doing so without planning can lead to deficiencies in fiber and B vitamins.

Which products contain gluten without you expecting it?

Sausages, soy sauces, bouillon cubes, conventional beer, some medications, and many potato chips processed on shared lines. Also certain yogurts with cereals and energy bars. Labeling is your best tool: look for "wheat," "barley," or "gluten" in the list of ingredients.

What happens to the body when you eat gluten and you are celiac?

The immune system attacks the villi of the small intestine, damaging the ability to absorb nutrients. This can cause digestive symptoms, anemia, fatigue, or dermatitis herpetiformis. But 20% of celiacs do not present obvious digestive symptoms, although intestinal damage still occurs.