Yoga affects weight loss on a number of levels, as you might begin to expect at this point.

1) Physically yoga builds muscle and burns calories (depending on one's intensity of practice, duration, etc).

2) Physiologically yoga affects our body's chemistry. In connection to weight loss, the most commonly studied mechanism is cortisol levels. Once again, thinking about this from an evolutionary stand point, it makes sense. For millennia, if early humans were stressed, it was often associated with conditions that might limit the availability of food. So what would our bodies do? Take whatever food comes in and store it as fat to be used during difficult times. It turns out that cortisol levels seems to be the linking mechanism between stress and holding on to fat. In our modern lives where stress is a day-to-day mode of living, our elevated stress levels cause an increase of cortisol and hence weight retention. Yoga counteracts this whole process.

3) Perhaps most importantly, yoga brings awareness to our actions. So much eating is habitual and somewhat unconscious. When asked what is enlightenment, a master responded, "Eat when you are hungry, sleep when you are tired." Though this is deceptively simple, the underlying truth is that most of us eat when it says so on the clock and sleep when our TV shows are done. Healthy, conscious eating is probably one of the single greatest benefits of yoga relating to weight loss.