I can't figure this out. OK, so grains like wheat don't want to be eaten, so they have antinutrients. If they actually don't want to be eaten, why don't they have poisons? It seems like the antinutrients they defend themselves with can have effects that could take decades to "take down" the wheat's predator. For antinutrients to have an actual detrimental effect that would discourage further eating of wheat seems like a plan that requires thousands of years to play out until the wheat-eater's species has succumbed to degenerative diseases to the point of not being able to reproduce anymore. Only then will the wheat have "won."
I can understand that maybe the antinutrients exist for some other reason and coincidentally affect us badly, but I can't get the idea that they exist because the grain doesn't want to be eaten straight in my mind.