Can food be fast? It's hard to imagine a hamburger with wheels or a bucket of french fries running like Usain Bolt. No, “fast food” must mean something else. Something profitable, often unhealthy, definitely successful: today McDonald's is the world's largest restaurant chain. It serves 70 million customers daily in more than 100 countries across nearly 40,000 outlets. In almost every city now a big bright yellow M stands for the hungry and disengaged bellies.