Does Mannitol affect blood sugar?

It has a minor impact on bloodsugar levels as only a small part of the ingested mannitol is partially absorbed and metabolised. It is passively absorbed in the upper gastrointestinal tract (as opposed to glucose which is actively absorbed). Mannitol is then partially oxidised into D-fructose by mannitol dehydrogenase and metabolised through a non insulinic glycogenolytic pathway. The major part of the ingested mannitol is not absorbed and goes through to the colon where it is fermented by the colonic microflora.