The short answer
Several factors usually contribute together. Different wheat varieties (heritage, spelt, einkorn common in Europe versus high-gluten industrial varieties in America), lower glyphosate residues from different farming practices, fewer dough conditioners and enzymes added during baking, and longer natural fermentation that pre-digests gluten and fermentable fibers. The relative weight of each factor varies by person.
Factor 1: Wheat variety and protein profile
American wheat is dominated by hard red winter wheat, bred over decades for high protein content and industrial baking performance. These varieties have higher levels of alpha-amylase/trypsin inhibitors (ATIs), proteins that trigger innate immune responses in some people without celiac disease[3]. European wheat includes heritage varieties, spelt, and einkorn with different protein profiles. A 2016 study in European Journal of Nutrition found that ancient and heritage wheat varieties had significantly lower ATI content than modern common wheat, with measurable differences in gut symptoms in sensitive people. This is why some non-celiac wheat-sensitive individuals tolerate spelt pasta and einkorn bread but not conventional wheat. The difference is not absence of gluten; both contain it. The difference is which specific wheat proteins you are exposed to.
Factor 2: Pre-harvest glyphosate practices
In the US and Canada, glyphosate is often applied to wheat as a pre-harvest desiccant, sprayed 5-10 days before harvest to dry the crop uniformly. This leaves residues on the grain. The European Union restricts this practice more strictly, and many EU countries have effectively banned pre-harvest glyphosate on wheat. Detected residue levels on European wheat are meaningfully lower than on American. Whether typical dietary exposure to glyphosate residues causes symptoms in humans is scientifically unsettled. Proposed mechanisms include gut microbiome disruption and mineral chelation. The evidence from low-level human exposure studies is mixed and inconclusive. Some of the European-vs-American difference is plausibly glyphosate, but it is unlikely to be the dominant factor. Wheat variety and fermentation differences are better supported by research.
Factor 3: Bread additives and dough conditioners
Commercial American bread typically contains additives that small-bakery European bread does not: dough conditioners (azodicarbonamide, DATEM, mono- and diglycerides), enzymes (alpha-amylase, xylanase, proteases), emulsifiers, and preservatives. Some of these additives can cause digestive symptoms in sensitive people through various mechanisms. Industrial enzymes particularly can leave residual activity that affects individual gut responses. Traditional European bakery bread (flour, water, salt, yeast or starter) has none of these. American artisan bakery bread with clean ingredient lists often causes fewer symptoms than grocery-store American bread, supporting the additive hypothesis. If the difference matters to you, reading ingredient lists and choosing bread with only flour, water, salt, and yeast is a cheaper experiment than flying to Europe.
Factor 4: Fermentation length
Traditional European bread, especially genuine sourdough, ferments for 12-48 hours. Industrial American bread ferments for 2-4 hours using commercial yeasts. The long fermentation allows lactobacilli to partially break down gluten proteins and fructans (a type of FODMAP) in the wheat[1]. This pre-digestion reduces the amount reaching your gut, which reduces symptoms in non-celiac wheat-sensitive people. A 2013 study in Gastroenterology showed that symptoms in "non-celiac gluten sensitivity" were largely driven by fructans rather than gluten itself[2]. Long-fermentation sourdough reduces both. The same wheat flour can produce very different symptoms depending on fermentation time. This is why some people tolerate authentic Italian sourdough but not commercially-produced "sourdough-flavored" American bread.
What to do with this
If you suspect wheat sensitivity but do not have celiac disease, try three things in sequence before concluding you need to cut wheat entirely. First, switch to genuine long-fermented sourdough for 2 weeks; buy from an actual sourdough bakery or make your own with a 12+ hour ferment. Second, try spelt or einkorn bread for 2 weeks. Third, read ingredient lists and buy only bread with flour, water, salt, yeast. If any of these resolve your symptoms, the issue was not gluten specifically; it was one of the factors above. If all three fail, you may have true non-celiac wheat sensitivity that warrants a full wheat elimination. For celiac suspicion, see a GI specialist for a blood panel and endoscopy before starting any elimination; diagnosis requires active gluten consumption. Tools like Aloe AI that correlate bread type to post-meal symptoms over a 4-week test make the bread-variety-versus-gluten distinction easier to see than a binary "I cut gluten" experiment. For the broader picture on food sensitivity, see hidden gluten and dairy in foods.