Almost every possible culture is represented in the culinary scene in Istanbul, and it's a city where you can go out for a meal every night, and try out something from a different culture, and never leave the one street.
Some of the best restaurants in the city serve Arabic and Turkish food, and this is well worth trying - the kebabs that you get in Istanbul rarely resemble what you might get in a British high street after the clubs kick out.
The food can be quite oily, and most dishes contain lots of meat, so forget about the diet while you're in the city.