Gluten: what it really is and how it works

What gluten is (and why the grain doesn’t contain it)

The most honest way to define gluten is to describe the experiment used to isolate it for centuries: make a dough of wheat flour and water, then wash it gently under running water. The starch and the soluble material drain away; what stays between your fingers is a rubbery, elastic mass that, once dried, is roughly 75-80% protein. That mass is gluten.

In the wheat grain itself, though, gluten as such does not exist. What exists are its proteins, stored inside the cells of the seed as a food reserve for the embryo of the future plant. They are reserve proteins, the kind a cell sets aside for later use: wheat evolved them to feed a seedling, not to bake bread. The continuous elastic network we call gluten appears only when flour meets water and hands (or a mixer) do the rest.

One clarification about cereals: in the strict chemical sense, gluten is a wheat story. Barley and rye contain closely related proteins, called hordeins and secalins, which behave the same way for people with celiac disease; that is why food regulations treat them as gluten for all practical purposes.

Gliadins and glutenins: the two families

Gluten proteins split into two families, present in roughly equal amounts, with almost opposite characters.

	Gliadins	Glutenins
Structure	Single (monomeric) proteins	Polymers of many subunits
Types	Alpha, beta, gamma and omega	High molecular weight (HMW) and low molecular weight (LMW) subunits
Size	30,000-75,000 daltons	HMW subunits of 65,000-90,000 daltons, joined into far larger polymers
What they give dough	Viscosity and extensibility	Elasticity and strength
How they bind	Weak interactions, mainly hydrogen bonds	Disulphide bonds between chains

Glutenins build the frame: three-dimensional networks of protein chains welded together by disulphide bonds, sturdy chemical links between sulphur atoms. Gliadins slip into that structure and soften it, interacting through weaker forces. The result is a material physicists call viscoelastic: it lets itself be stretched like a thick fluid and springs back like a coil.

The chemistry of these proteins is unusual: between roughly 20 and 50% of their amino acids are glutamine, and proline reaches 10-30%, concentrated in long, nearly identical repeated sequences. That repetitiveness will matter again when we get to celiac disease: according to Shewry’s review, all 31 protein fragments recognised as relevant to the disease sit precisely in those repetitive regions.

Practical example: the washing experiment works in a home kitchen. Knead 100 grams of wheat flour with a little water, then rinse the ball under the tap inside a sieve: the water turns white with starch and you are left holding a greyish blob that stretches like chewing gum, which is nearly pure gluten. Try the same with rice flour and you get only mush, because the network-forming proteins are missing.

What it does in dough

During kneading, the hydrated proteins from the flour’s individual cells hook onto one another until they form a single continuous network wrapped around starch granules and air bubbles. When yeast ferments the sugars and releases carbon dioxide, that network behaves like the fabric of a hot-air balloon: it tightens, it swells, but it does not tear. This is why a wheat dough rises and keeps its honeycombed structure after baking.

The balance between the two families decides the dough’s temperament. More weight on the glutenin side means a tenacious dough that resists and pulls back; more weight on the gliadin side means a dough that lets itself be stretched. Bakers have played with this balance forever without needing to name it.

The dependence on disulphide bonds can be shown in the lab with a single gesture: add a reducing agent, which breaks exactly those links, and the network collapses, taking the dough’s properties with it. Shewry describes the effect on functionality as “catastrophic”: without those welds between chains, gluten stops being gluten.

Practical example: anyone stretching a pizza feels the two families at work. When the disc widens obediently under your fingers, the gliadins are on duty; when a moment later the rim shrinks back towards the centre, the glutenins are calling the net back into shape. Resting the dough serves exactly this purpose: giving the network time to relax so it can be stretched without fighting back.

Celiac disease, described without alarm

For most people the story ends there: gluten is the protein that gives bread its structure. In about one person in a hundred, however, the immune system reads those repeated glutamine-and-proline sequences as an alarm signal.

Italy’s National Institute of Health (ISS) defines celiac disease as a permanent inflammatory disease of the gut, triggered by eating gluten-containing food in genetically predisposed people: an autoimmune disease, in which the reaction to gluten ends up damaging the gut’s own healthy tissue, in particular the villi, the microscopic folds of the intestinal lining through which nutrients are absorbed. The predisposition lies in normal variants of genes in the HLA-DQ region, written in the DNA like any other inherited trait: carrying them does not mean falling ill, they simply mark the predisposition. Two cases out of three are women.

The symptoms span a wide range. The classic form shows up in the gut: diarrhoea, bloating, abdominal pain, weight loss, slowed growth in children. The atypical form is more elusive and can present as fatigue, mouth ulcers, menstrual disorders or osteoporosis; there is also a skin form, dermatitis herpetiformis. Diagnosis follows a precise path: first a blood test for anti-transglutaminase and anti-endomysium antibodies, then confirmation with an intestinal biopsy. The only treatment available today is a strict, permanent gluten-free diet, which reverses the symptoms and prevents complications.

Italy’s numbers give a sense of scale. As of 31 December 2023, 265,102 people had a diagnosis, with 13,163 new diagnoses in a single year (there had been 10,210 in 2022). Since celiac disease affects about 1% of the population, the expected number of cases in Italy is around 600,000: the diagnosed are just 37%, meaning hundreds of thousands of people live with the disease without knowing it. To close that gap, a pilot paediatric screening project has started in four regions (Lombardy, Marche, Campania and Sardinia), looking for celiac disease and type 1 diabetes in children and teenagers aged 0 to 17.

The gluten-free market: what the research shows

A market has grown up around gluten, reaching far beyond celiac disease. Up to 13% of people report some sensitivity to gluten, and about 5% of the Western population says it follows a gluten-free diet: five times the share of those with a documented need.

Research has tested this self-reported sensitivity with the strictest tool it has, the double-blind study, where neither the participant nor the experimenter knows who is eating gluten and who is not. The result scales the phenomenon down without erasing it: only about one third of people who believed they were sensitive showed symptoms with disguised gluten, and the nocebo effect, feeling ill because you expect to, has been estimated at up to 40%. Here too, as with other food topics, beliefs outrun the data: it happens with creatine as well, a textbook case. The heart of the matter is the gap between what gets repeated and what experiments confirm.

As for the idea that gluten-free products are healthier across the board, the studies gathered by Diez-Sampedro and colleagues observe the opposite: a gluten-free diet can end up lower in fibre and in several micronutrients (calcium, iron, magnesium, zinc, vitamin B12, folate, vitamin D), at prices 2 to 3 times higher. For people with celiac disease these products are a daily necessity, protected by law: in the European Union the statement “gluten-free” requires a content no higher than 20 mg/kg, while “very low gluten” allows up to 100 mg/kg. Thresholds designed to protect those who genuinely must avoid gluten.

All told, the balance is calmer than the supermarket shelves make it look. Gluten is a pair of protein families with a rare talent for making a net; for 1% of the population it is the trigger of a serious autoimmune disease with a well-defined diagnostic pathway; for everyone else, the available research has found no reason for fear.