I have a biggish belly and it does cause my back pain, no doubt about it. But I started running about a month ago and guess what? No back pain anymore. I thought it would be the opposite to be honest. It must be to do with the core muscles getting stronger. I don't think my belly has shrunk that much;-)
I also did Kundalini Yoga for a few years and was never better. Fitness and health all sorted with only one night a week. Very powerful. I must get back into it. lol