Dies adding fiber supplement help or hinder. My formula has no fiber in it.

Fiber helps your body digest what it takes in and yes it will help you with diarrhea. But you must be careful to use the correct type of fiber. Look for soluble fiber (absorbs water) for help with diarrhea. If you are constipated you would want to use insoluble fiber (fiber that is not digestible). Insoluble fiber will make diarrhea worse.