Maybe you could actually go WITH their Christian leanings by explaining to them about how modern grains have been engineered in a lab, etc. Surely that was not in God's plan. Tell them about all the artificial colors and flavors, also created in a lab not by the Almighty. Explain to them that you are trying to eat more like Jesus would have, real whole foods.
The book Wheat Belly by Dr. William Davis might be a place to start. It explains why modern wheat is so harmful.
Remind them who will be choosing their retirement home.
In the meantime, do what you can quietly and try not to create pointless confrontations.
Loneketo - you poor wee thing. We parents think that we are right most of the time - but sometimes we are not.
I agree with above....try and keep confrontations to a minimum.
if you need to let off steam - go and whack a tennis ball at a wall, or sprint up and down the road, get out of the house.
perhaps you could have a conversation with them something like....Mum and Dad I love you to bits, but I do not like the way you treat me over our family beliefs. Please let up a little !!!!
anyway good luck
"never let the truth get in the way of a good story "