Really depends on your provider, but often you get a 'choice' as it were, in that you can choose to do what they call the 'milk diet', which as the title suggests is predominantly drinking milk, although you are allowed other things like smoothies, NAS drinks, sugar-free jelly and the like. Alternatively, you may be able to choose the 'low fat, low carb diet', which again as the title suggests is a carefully calorie controlled diet that is low fat & importantly, low in carbohydrates. Full diet details should be provided by your health care provider as to exactly what they say you can and cannot have, as these details vary greatly from place to place. Which one you choose (if you get a choice) will mainly depend on what you personally think you can manage best with for the time period you need to be on the diet.