Soon, an article on tummy reduction:) But if you have been following our yoga series, you can start try some from them: Navkasana (boat pose), from here Udarakarshanasana or abdominal twist. And definitely kandharsana from the above set. In fact, abdomen becomes slack and sags due to a weak spine which does not support its muscles -- so I would say, the above five poses will trim tummy if you do them regularly.
