Can probiotics cause weight gain ever?

No weight gain: Probiotics are bacteria that should normally inhabit the colon. There numbers are estimated to be 200 trillion in an optimaly healthy bowel. There job is to not only break down food, but to provide defense against harmful bacteria in our food, produce b vitamins and vitamin k, and provide for the conversion of thyroid hormone (t4) to its active hormone t3, (liothyronine) they do not cause weight gain.