if you really want to trust the ratios nature provided then you should just chew the grass, not juice it. there are no juicers in nature, thus the ratio in the juice is 'unnatural'. so if you want to be totally natural you shouldn't juice since juice doens't exist in nature, only whole foods.
i think we can get too hung up on 'natural'. is living in a house 'natural'? is writing messages to each other across the world on the internet 'natural'? lots of things may not be 'natural' but that doens't mean they aren't good to do. Nature gave us a brain and that brain can be used to create highly effective protocol for health. and those protocols may, or may not, appear in nature. thats the way i see it anyway.