The reason why you can eat bread in Europe but not the US is because of the differences in wheat types as well as differences in additives, and the fermentation processes result in better digestibility of the bread.
Bread in Europe also often uses softer and lower gluten wheat as well as longer fermentation times.
And bread in the U.S. often contains more additives that can be made from higher gluten wheat, which makes the U.S. bread being harder for some people to digest.
Europe grows more soft wheat, which is also lower in protein and gluten.
And North America grows mainly hard red wheat with higher protein and gluten content.
The United States also allows certain chemical additives in the bread and in Europe the chemical additives are banned from being added to bread.
These substances and chemical additives that are often in United States made bread are potassium bromate and azodicarbonamide, which can also cause issues with digestion for some people.
European bread, unlike U.S. bread, especially the traditional sourdough bread, often has a longer fermentation period.
And this longer fermentation process also helps to break down the gluten as well as other compounds, which makes it easier to digest.
And some wheat in the United States is also suspected to be using an herbicide called glyphosate, which is usually widely used on U.S. wheat crops and can result in digestive issues.
And several European countries have restrictions in place on the use of the herbicides like glyphosate, although both regions also import wheat that might have been treated with it.
And when traveling in Europe, you might be more relaxed and more active, which can also improve your body's digestive process.
And eating of a large, slow midday meal is more common in some European cultures than eating on the go, which is more typical in the U.S.