Yea, lectins can be nasty. Mainly the ones in grains (especially wheat.)
They are "anti nutrients" which can block the absorption of nutrients.
Phytic acid does this too, and that's found more in "brown" types of grains, like brown rice.
While it may have more nutritional "goodness" on the nutritional facts on the back of the box/bag... Studies show that white rice over brown may have a better nutrient absorption, and therefore be equal to, or better than brown rice.
So lectins + phytic acid = no good.
And that's one of the big reasons to avoid grains.
But yea, I'd actually think that white bread (especially sourdough) and white rice are better than brown rice or whole wheat.
Lectins, if they get into your bloodstream, can also bind with your insulin receptors and could make you more insulin resistant, and also can mess with your leptin.
That could lead to insulin resistance, and constantly feeling hungry... and you'd probably be hungry for the same "whole wheat goodness." Which would repeat the cycle.
Add some sugar and... BAM!
That'll kick it into overdrive.
Unfortunately that's the story of a large number of people in the "western" world today.
I believe its the phytic acid and phytates that stop mineral uptakes.
Lectins sort of scrape the mucous coating off of the intestines, although it's repaired virtually instantaneously. The real danger of lectins is that they can pass through the intestinal wall right into the blood stream where they mimic our good proteins, thus getting into our cells, thus causing illness. Whew!