When he serves the food, is it possible to tell him you just don't want any potatoes or carbs, or better still, you can serve the food yourself. Also nothing wrong with making better choices, drink the water. Or to solve the issue, you can just be HONESt and tell him regardless of the criticism he may give. whats the worst that could happen? He may discourage you, but if you are already sure that this is what you want then you might just have to ignore. When he sees your dedication perhaps he will support you.