Didn't want to leave out tomato, since you said that was a large part of your diet:
Influence of saponins on gut permeability and active nutrient transport in vitro.
Saponaria saponin and alpha-tomatine
also reduced transmural potential difference, but soya saponins were much less effective. The results indicate that some saponins readily increase the permeability of the small intestinal mucosal cells, thereby inhibiting active nutrient transport, and facilitating the uptake of materials to which the gut would normally be impermeable.
I'm going to save the rest for my article, just wanted to give you a taste of the research showing that GI tracts don't like the nightshades at all...
Just wait for the article on peppers, that one will be brutal.