It sounds like the cause of your stuttering is very similar to mine, which I also feel is strongly tied to my stomach health. I too benefit from lecithin (and phosphatidylcholine), but another big one I've found is is butyrate. It's a short chain fatty acid that is normally produced by gut bacteria when fermenting dietary fiber, and is important for enhancing gut permeability and reducing inflammation, but dietary fiber for me tends to cause too much bloating and other problems in high quantities. I've found supplemental butyrate always helps immensely with both verbal fluency and gut pain/bloating. I also find avoiding reflux triggers like acidic or high histamine foods help too, since when I get persistent reflux symptoms my chest, neck and face muscles get tight and it becomes physically harder to project my voice, leading to more stuttering when I have to speak louder.