Nearly all plant foods are going to contain toxins in one form or another. Avoiding said foods would result in an extremely bland diet lacking in micronutrients. The lesson learned here is that variety is a crucial element of any healthy eating program. By constantly rotating your food choices, you avoid the potential problems associated with accumulating high levels of specific toxins.
DeVany talks about this in great detail on his blog, and applys the same logic to rotating macronutrients. By rotating carbs, protein, fats, and foods, we're not only ensuring a surplus of nutrients necessary to optimize health, but also avoiding the potential health problems created by monotonous/static approaches to nutrition.