[bregma]

It's more the opposite: FODMAPs are non-fermentable carbohydrates. If they were fermentable by yeast, they would be fermented and you wouldn't be eating them. The whole point is that yeast doesn't metabolize them but your natural intestinal flora does.

Sourdough is a mixture of yeasts, lactobacter, and acidophilus in various proportions. The latter two will metabolize the FODMAPS, either while proving the bread or in your gut. One of those choices can cause discomfort and the other a delicious food product.