Depends on the diet....if you mean an Atkins style "carbs are bad" diet then most protein rich foods are ok...cheese, meat, milk, mushrooms etc etc. These tend to have a lot of fat with them, though, so if you really mean protein only thenits artificial foods only, really. As to how sensible it is.....depends on you. A diet like the Atkins will be high in cholesterol, low in fibre and possibly lack some nutrients (for a balanced remedy to all this see Atkins himself...he does answer all these problems). It still leaves you constipated, though, and you should be carefull if you have any blood cholesterol problems. If you are youngish and healthyish then you can stay on it for a good while. The old problem with diets is that when you come off them you tend to put the weight back on, as you havent changed your lifestyle.