I don't have any particular advice to offer you, other than to be ready for a lot of complaining when you win. "Men have it so easy." "A woman's metabolism just starts to slow down in their 30's." "You must just be the type that loses weight effortlessly."
I assure you, it will have nothing to do with your discipline and effort (or the pizza rolls they've been eating) in their minds. It will be unfair, and it will be YOUR fault.
Good luck with that