Seven might not be so sexy with the body of Tony Soprano.
If she didn't have to exercise and eat right to make her body, then she would have had Tony's body eventually, which is why the Doctor wouldn't have made her super fit rather than give her a goal to work towards. It's totally teach a girl to fish.
Sexy is what you do with what god gave you, no matter what god gave you.
Beautiful is some fluke when you win gods lottery.
If you're beautiful you don't have to try to be sexy.
Ugly girls try harder.