In the Netflix documentary “Miss Americana”, she says she used to starve herself, in her early twenties.
Spending an evening singing and dancing, she used to be exhausted after a concert.
Now she is eating regularly, she can easily handle all that physical activity.
She must be working out, quite a bit, too.
She does not look fat, but rather stronger.
Even her upper body is quite toned.
Being fit is rather useful for coping with long tours and the celebrity lifestyle.
And she is not known for using drugs.
Yes, sure, working out is much safer than cocaine, and she looks gorgeous, no matter what.