Gluten

Gluten is the protein complex (gliadin and glutenin) that gives wheat-based dough its elasticity. It's found in wheat (including spelt, kamut, durum, semolina, farro, einkorn), barley, and rye, and as a contaminant or thickener in many processed foods. Oats are gluten-free by nature but commonly cross-contaminated during processing.

There are three distinct gluten-related conditions, and they're managed differently. Conflating them is one of the most common sources of confusion in nutrition advice.

Celiac vs NCGS vs allergy

Celiac disease is an autoimmune condition — gluten triggers immune destruction of the small-intestine lining, causing malabsorption and long-term complications. It affects ~1% of the population and requires lifelong, strict avoidance of even trace gluten. Diagnosis is by blood test and biopsy — both require still eating gluten, so don't go gluten-free before testing. Non-celiac gluten sensitivity (NCGS) is a separate diagnosis where people report symptoms (digestive, headache, brain fog, fatigue) on gluten without celiac antibodies or wheat allergy; the mechanism is unclear and some research suggests fructans or other wheat components — not gluten — may be the actual trigger in many. Wheat allergy is an IgE-mediated response to wheat proteins and behaves like a classic food allergy.

Don't go gluten-free before testing

If you suspect celiac, get tested first — going gluten-free before testing produces false negatives. A gluten-free diet is restrictive, more expensive, and often lower in fiber and B vitamins; nobody should adopt it without a reason. If you don't have celiac or wheat allergy but feel better off wheat, a fructan elimination (also cutting onion, garlic, and other fructan sources) is worth testing — many "gluten sensitive" people turn out to be reacting to fructans instead.