Food is essential for surviving and if you don't eat you will die. Hunger is represented by a chicken leg and if it goes red it means its below 10 percent. Hunger diminishes slower then thirst. Food is easy to come across and if you want a reliable source of food make a cropplot or start fishing for mackerels.
Hunger is one of the few threats. The others are thirst, shark and lack of common sense. The hunger bar will glow red when it hits 10% so you must eat before it hits 0 other wise you will die. The hunger bar represents the minecraft chicken leg however when it is released on steam it will become a bar with 2 lines.