BESIDES annoying the food industry, the Government's draft guidelines for a healthy diet have been greeted with much groaning and anti-nanny propaganda from columnists. This was to be expected because the food the guidelines want us to eat less of is nicer than what we are told to eat more of. The very word diet is enough to cast gloom.
Yet its origins are harmless, even benign. It came from the Latin diaeta, from the Greek diaita, meaning a mode of life, in which food played an obvious part, and there was no reason why a diet should not be pleasant. When, according to the Authorised Version, the then king of Babylon (whose name was Evil Merodach) released Jehoicahin king of Judah, he commanded he be given 'continual diet' - in other words he fed him well to compensate for the prison food he'd been having. Sydney Smith said praise was the best diet and he presumably thought you couldn't have too much of it. The participle dieting, in the sense of eating less to keep thin, is quite modern; before, it merely meant having, or giving, rules about eating. I suppose the fashion industry must take the blame for this dismal semantic change.
In my schooldays diet was a joke word because of the of Worms. Our teachers told us that this was a pretty feeble pun, that the D of W was the assembly which outlawed Luther in 1521, and that diet here had nothing to do with food and came from the Latin dies. A diet in this sense was therefore a sort of day conference, or perhaps a daily one.
The real answer is more complicated, and a feast for etymologists. They agree that both senses came from diaeta, which was taken to mean the regular business of life, which in turn came to mean daily offices or functions, all because the writers of medieval Latin got diaeta muddled up with dies. In his Etymological Dictionary, Walter Skeat, the Victorian authority, called this a 'peculiar use', by which he meant special or particular, rather than odd or strange.