>In 1869, tinned mutton was introduced as rations in the British Navy. Far from being a tasty cut of meat, sailors complained their food was so awful they suspected it was the dismembered body of Fanny Adams. Soon the grotesque joke had spread so far that tinned mutton was referred to as a tin of Fanny Adams.

>To this day British sailors are served their rations in what is nicknamed a 'Fanny'. As often happens with language the slang phrase 'Sweet Fanny Adams' soon filtered into wider society where it became a euphemism for anything not worth having or 'nothing'.

Sweet Fanny Adams > Sweet Fuck All

For anyone who is as lazy as me and didn't want to scour the article for the reasoning.