Another reason is low nutrient values. We use plants as the medium to eat soil. If the soil lacks nutrients, the plants don't uptake much of it, and it doesn't get passed onto us.

Same for animals, we feed them nutrient deprived corns. You simply can't get something from nothing. Now you eat that and then your girls breast milk is lacking, then the baby is lacking.

I could write for days about this type stuff if your interested.