Weight Loss & Yoga
I translated and wrote commentaries on some traditional yoga books. Such books are Bhagavad Gita, Yoga Sutras and Hatha Yoga Pradipika. Up till now, in those texts, I found no motive for doing yoga as being losing bodily weight. Health benefits are mentioned in the Hatha Yoga Pradipika when that texts discusses asana postures but health is not listed as the motive for doing yoga in any of these books.
I feel that if one does asana postures primarily as a means of losing weight, one will eventually become discouraged from doing the postures. For one thing asana postures is not yoga but is one of the eight (ashta) parts of yoga. Hence a motive for doing asana postures as a system in itself departs from yoga as the postures are a part of yoga. Nowhere does it state that asana is the major part of yoga. The major part according to the stress placed on it by Patanjali are the three higher parts which are listed together as samyama. These are dharana, dhyana and samadhi as one sequential practice.
Instead of doing asanas to lose weight, my suggestion is to do asanas to curb the diet and the time of eating. Curb the eating habits which support unwanted weight gain. Do postures which help you to gain control of what you eat and which cause you to better manage when you eat. But as Patanjali defines it, asana postures are only one part of the yoga syllabus. It is not yoga in completion.