I don't want to offend your family, because I know people can be very protective, but I may. Here goes.
If your family doesn't understand it's one thing, but if you've explained to them and they "refuse" to understand then they're just being ignorant.
Remember, what you're doing you need to be doing for yourself, not for them. I know it's your family and it's hard to say, "Who cares what they think," but you need to. You need to ignore what they say, add some bulk and then when you cut you can go back and say, "See, this is what I was aiming for."
It's always satisfying to say, "I told you so," without having to say, "I told you so."
Just remember why you're doing it and who you're doing it for. You're doing it for YOU and that is the only person who you should allow to effect your self-esteem.