There are certain things that grow that would just not be too good for us. Poison ivy and certain mushrooms like night shades are not good to eat. God did not intend for us to eat of certain things, He expects us to use our common sense that He gave us. Certain animals are scavengers, they would not be healthy for us to eat. God used certain birds, animals and creeping things as His version of disposals. They eat garbage and turn it into useful "fertilizer". Pigs, dogs, buzzards and crows and bottom feeding fish are examples of garbage disposals. You eat food, but you would not want to eat your garbage disposal. God does the same things in nature.
Here is a link to a good article on the subject.
To Eat Or Not To Eat...That Is The Question