Well, I do remember reading in a article about vitamins, of sugar(refined sugar) being known to deplete the vitamin B2 in your body. I don't think bad bacteria can hinder absorption but Sugar feeds bad bacteria so I guess in a way it does. Good bacteria ,on the other hand, helps the body absorb the nutrients from your food. In fact good bacteria supposedly produces B vitamins in your intestines so that they can absorb the nutrient from the digested food ( I'll try to find where I heard that from).