It leans you out. You will start building muscle so eventually you will maintain or gain weight. Unless you are obese a big chunk of fat does not weigh much. You are gaining control of your core where most of your fat is probably at. After a while your core turns into muscle thus gaining weight. You are actually using more energy than you think doing yoga but you have control of your heart rate so you burn fat instead of muscle. Stick with it and you will notice in your workouts that your strength becomes more practical. So instead of isolating your muscles when lifting you will you use more of your core and other muscles including muscles you did not realize mattered. I am no expert but this has worked for me and has made the biggest difference in my life. I am 36 and am in the greatest shape of my life mostly because of yoga.