Kinda sorta just picked it up when summer came and I noticed I gained a little weight. Not a lot but enough to be self-conscious about it. So I was constantly walking around and working with taut/pulled in abs to flatten the stomach, only time I really relaxed them was at home and when completely alone or going to sleep. At some point my default diaphragmatic breathing switched to default costal breathing, simply there wasn't any space for my lungs to expand down/out into for most of the day. As for whether or not it works for stuttering... it worsened. Had blocks and slurs I never had before. Seriously guys, relax that belly and let that phragm do its work.