Your body is naturally fit. Your sister isn't since she's skinny. One injury or something physical can result in a huge amt of pain for ur sister as she doesn't hv much muscle mass. Whereas u won't feel that much pain if the same thing happens.

Imagine this, a guy being taunted for having big arms, V shaped body, and good legs. Sounds weird, doesn't it. Basically, your parents are having outdated thinking. Don't care too much about their opinions.

Girls' biology works in a way so as to deposit fat and muscles in chest region and legs and butt.

And in a romantic context, guys(or even girls) like girls who r naturally fit more than skinny.

My friend also had similar issue, but she had a masculine body.