I dont see what the big deal is if all they do is heckle you about it. Making you pay for food, on the other hand, I could see as being a problem.
I went to costco with my mom the other day and bought over $400 bucks worth of drinks, eggs, turkey, chicken, steak and salmon. She bought some other stuff for herself too, but not a significant amount.
My mom questions my eating habits, but she puts up with it anyway.