In case you were wondering what happens when you completely substitute yogurt for the fats in a muffin recipe . . .
I used plain yogurt to replace the oil AND the milk in a basic quickbread recipe (flour, baking powder, salt, sugar, egg...and supposed to be oil and milk)
It came out VERY CHEWY, like some kind of specialty bread. It was such a surprise texture for me - I'd added yogurt to recipes in the past, just never so radically.
No tragedy, just a quick weekend lunch experiment (for friends...) with fresh peaches/brown sugar on top!