Bitters promote digestion. You likely are expelling a bunch of toxins and crud from deep in your gut and this is is why your bm’s are different. One of the goals of the diet is to get things to travel through the gut as quickly as possible, and bitters definitely promotes this.
One thing you will notice is that your bm’s will change throughout your treatment; some days are good, some are bad. It varies like the weather.
Hope this helps.