Bread which is left out can have any number of things happen to it, all of which are usually progressing at once, although one will win out as the primary thing you experience:
- It goes stale, that is, the starches in the bread lose their hydration and re-crystallize giving the bread a harder texture
- It dries out, losing moisture to the atmosphere (or if it is very humid, it can get soggy, gaining moisture from the air)
- It molds, if it is moist enough for molds to thrive
- Its gets eaten by humans, insects, dogs or other large scale breadophilic creatures
The only question is which happens first or most dominantly.
This can depend on the moisture level in the bread, natural anti-bacterial or anti-fungal agents in the bread (like honey) or artificial preservatives, the particular environment the bread is in (and how many mold spores there are)--any place that has had moldy bread is going to have more mold spores for future moldy bread than average.
I would not try to relate any of this to nutrition, or to a veiled evaluation of the relative quality of benefit of the bread that is available in one country or another.
The notion that mold requires nutrtion is true, but it is not the whole picture: it also requires a hospitable environment (pH neither to high or low, not to much osmotic pressure from salt or sugar, sufficient moisture) and so on. Chocolate is extremely nutritious in the sense that it is composed nearly 99% of things that are metabolized, but it does not host molds because it is also 100% dry. Dried salted cod, again, highly nutritious, but not hospitable to molds.
You cannot take only the growth or non-growth of molds as an indicator of level of nutrition.
Furthermore, the notion of "nutritious" is extremely complicated. It involves requiring sufficient calories (as from fats or sugars), as well as vitamins, minerals and other micro nutrients. It is not a simple yes or no thing.