This I feel is an embarrassingly stupid question, but when folks recommend marshmallow for slowing down the gut, do we mean the gelatin-based confectionery product which is all that is commonly seen in the UK, or the plant marsh-mallow Althaea officinalis, which has been used as a herbal remedy in the past, interestingly for the relief of irritation of the mucous membrane.
I suspect it is the former gelatin-based sweet, which is not great if you are an aspiring vegan. Intriguing to know why gelatin has this effect though.