In order for us to live we must consume other organisms which have lived.
This amazing menu is available to us because these organisms have been able to have a life. The quality of the life they have had would logically seem to have an effect on the quality of the food which they provide.
The food we eat supplies our bodies with the materials with which to miraculously continue our lives. The higher the quality of the food that we can eat - the better the materials with which our bodies are made - it seems the better we will feel.
I mean really - the better Earth feels - the better we will feel.
Concern for the environment is completely selfish really - and that is okay - that is how we survive.