Three days is enough time to understand Istanbul's food culture — if you structure it correctly and resist the urge to eat everywhere at once.
The first-timer's instinct in Istanbul is to eat as much as possible as quickly as possible, which is both understandable and counterproductive. The city has several distinct food cultures running in parallel — street food and fine dining, Bosphorus seafood and Anatolian classics, European-influenced Beyoğlu and traditional Asian side — and the person who tries to sample all of them in seventy-two hours tends to leave with a confused impression of each.
A more useful approach is to structure each day around a neighborhood and let the food follow from the place. Day one belongs to the historic peninsula — Sultanahmet, Eminönü, Karaköy — where the oldest layers of Istanbul's food history are still visible. Start with a simit and tea at the Galata Bridge fishermen, lunch at Pandeli above the Egyptian Bazaar, an afternoon of baklava at one of the traditional shops around the Covered Bazaar. For dinner, walk down to Karaköy and the modern waterfront restaurants that face the Golden Horn.
Day two crosses to the Asian side. Kadıköy market in the morning — the produce here is as good as anywhere in the city, and the surrounding streets hold excellent breakfast spots, cheese shops, and delicatessens — followed by lunch at one of the meyhanes on Moda Caddesi. This is Istanbul at its most straightforwardly pleasurable: good wine, shared plates, a table full of people who have nowhere particular to be.
Day three should be spent in Beyoğlu and Nişantaşı. This is Istanbul's most European-facing neighborhood, and the food reflects it: specialty coffee at a third-wave cafe in the morning, a long lunch at one of the upscale restaurants in Nişantaşı, drinks and small plates in the early evening at one of the wine bars around Asmalimescit. By now, if the itinerary has worked, the pattern should be visible — a city that understands food as a form of sociability, not just sustenance.
A few practical notes: make reservations for dinner, always. The best restaurants in Istanbul fill up, and waiting does not improve the experience. Learn to say buyurun (welcome, here you go) and tesekurler (thank you) and the whole experience becomes warmer. Eat at mealtimes — lunch between twelve and two, dinner after eight — and resist the urge to snack constantly. The best meals here are eaten slowly, with time for the food to settle and the conversation to wander.