Mostly, I think, it helps flexibility and strength. As in it's not the fastest way to lose weight, but no dobt helps in the long run.
I know a couple of people who do it for fitness (I think once a week with an instructor and like 20-30 minutes per day at home) and none of them are painfully thin. One of them is actually on the rounded side - but still can do a handstand.
I've never asked about the exact type of yoga they do since I have no idea about that as it is.
None of them do any of the other yoga stuff though, which includes diet and the yoga diet will probably leave you thin, it's something like vegetarian only with basically no overly processed foods, loads of sugar, oil etc... and never overeating, you get the picture.







