In most restaurants, the food itself is a loss leader. The real money is in booze and drinks. Why most diners back east have a bar. All the money is made in the bar drinks.
Times have changed and more people are there for the food and not for the drinks, so the business models change.
Food cost isn't typically a loss leader, but (American sense) entrees are often aimed to be around neutral because people judge mainly on that when they peruse menus. But that's neutral including loss.
Desserts margins are similar to booze, often. Appetizers make them money, as do sides and upsells.