1976 commercial for McVitie’s Digestives.
A digestive biscuit, sometimes referred to as a sweetmeal biscuit, is a semi-sweet biscuit popular in the United Kingdom and in other Commonwealth countries, as well as in Ireland and in Greece. 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.
Digestives are known at least as far back as advertisements for Huntley & Palmers in 1876, with a recipe being given in 1894 Cassell’s ‘New Universal Cookery Book’ of 1894.
Although rumours exist that it is illegal for them to be sold under their usual name in the United States, they are in fact widely available in imported food sections of grocery stores and by mail order.
McVitie’s Digestives now have a disclaimer that “The ingredients in this biscuit do not contain any substances that assist digestion.”
Info gleaned from Wikipedia