Buns are very tasty. They are also lexically very productive, and appear in all sorts of phrases and idioms far removed from the 'sweet bread or cake' meaning.
I was watching the third episode of an interesting BBC series about women in the Restoration period (can be viewed if you're in the UK here), and prostitutes of the time were known as 'buttered buns'. Bun is an old dialect word for 'rabbit', and since rabbits are known for their mating habits, perhaps that is how the word came to be applied to women. 'Butter' as a verb often implies embellishment eg fine words butter no parsnips, or to butter someone up.
To have a 'bun in the oven' means to be pregnant. Perhaps the bump resembles a bun. The OED says there is an old French word bugne, meaning 'swelling', so that's a link, too.
A bun-fight is a jolly party with lots to eat. To get (have or tie) a bun on is a dated slang expression meaning 'to get drunk'.
Another word used during the Restoration period (ie the 1660s) to apply to women, albeit not prostitutes, was 'silkworm'. This is in the OED with the sense that was used in the aforementioned TV programme, namely "a woman given to frequenting drapers' shops and examining goods without buying". Lucy Worsley, the presenter of the programme (Harlots, Housewives and Heroines) related how this period in history saw an increase in interest in fashion, after the domination of the austere views of the Puritans during the previous decade.