hi
This is what it says on wilipedia
A digestive biscuit, sometimes referred to as a sweet-meal biscuit, is a semi-sweet biscuit originated in the United Kingdom and popular worldwide. The term 'digestive' is derived from the belief that they had antacid properties due to the use of sodium bicarbonate when they were first developed. Historically, some producers used diastatic malt extract to 'digest' some of the starch that existed in flour prior to baking.
More here
http://bakingforbritain.blogspot.com...-biscuits.html
Hope this clears things. Chrissie