Gaining

You may want to wait until you're independent. If your parents put you through too much crap over your weight it might not be worth it.

On the other hand, if they don't, what's the problem?

I used to smuggle little debbies into the house in my backpack and stuff my face when everyone was asleep. Eat a burger on the way home and then have another lunch at home.

If you're creative enough you'll figure it out.

Unless your parents are overweight too and love to eat. My mother might be a feeder, as she loves to see me eat and also to cook for me ;-)
I have gained quite a bit but she does not seem to connect the dots and it just happy that I'm happy.
My parents are not massively obese and watch their weight and eat high quality food, not crap or fast food, so their health is good, even though they are big.
I think there can be different ways to eat food, they seem to eat it because they enjoy it so much and are gourmets, it is not a compulsion or anything, so that might be the reason they are more positively inclined towards it.
So just wanted to give you a nice example that not all parents will be hell bent on making you feel bad for gaining.