The importance given to diet in medical treatment has had many ups and downs in the past 300 years. Nutritional science was rudimentary in the eighteenth century,1 but diet was probably a better option than the alternatives of bleeding or purging. At the beginning of the twentieth century many young men recruited for the Boer war were found to be seriously undernourished, so a school meals service was introduced. The golden period for nutrition was the 1930s, when most of the vitamins were discovered and shown to be therapeutically effective - in 1932, for example, the death rate among children with measles in a London fever hospital was reduced from 8.7% to 3.7% by a daily supplement of vitamin A from cod liver oil.2

The rationing system during the second world war was a spectacular …