E! Magazine has revealed details about the extreme Sirtfood diet, which Middleton is understood to be following. This diet, labelled "faddish" by some, consists of eating foods rich in sirtuin proteins, or SIRT1 - SIRT7, which are are known to contribute to fat and glucose metabolism regulation. Key foods of this diet include kale, blueberries, citrus fruits, nuts, dark chocolate, red wine, prawn and salmon. While this might sound pretty reasonable (red wine!) it is the quantities of food consumed over the diet cycle that has nutritionists concerned.