I want to inform you at the outset that I somewhat updated my opinion on this recently. This post reflects my current opinion. The need of this post came because probably one of my friends became little concerned when I advocated slim abdomen for Yoga poses.
While I agree that Yoga exercise is meant for anyone and everyone, including big, small, slim, weak and strong, every Yoga exercise is not meant for everyone. It is something like this, “anyone who wants to purchase a car should feel free to purchase any car they like, but that depends on how much they can pay for the car”. Someone who can only purchase Toyota Corolla may not be able to afford BMW. Also, one can walk any distance if they choose to. But, it will be irrational to think of walking from India to Thailand instead of using some transportation.
Thus, when a person does a particular Yoga pose, some pre qualification is necessary. One who wants to do the complicated poses need to have slim body for sure. And, those who do non complicated poses also benefit if their body is slim. And, those who do not have slim abdomen can actually get into harmful situation if they try to certain poses.
So, it is not a question of individual freedom or personal dignity, but it is a requirement. Therefore, in my Yoga Exercise style, I do not teach the same pose to all the students. Also, if a student is big and likely to have problems with a pose he/she wants to learn, I do not hesitate to tell them to slim down for that matter.
Above all, there are Yoga Poses that are meant for slimming down. And, Yoga scriptures clearly mention that a Yogi should be slim! (Hathayoga Pradipika, Yoga Sutras of Patanjali, etc.)
I want to inform you from my personal practice and also teaching practice of prolonged time: anyone who cannot control their diet are not likely to progress in Yoga much.