A lean diet of food grown on the island and a philosophy of moderation-"eat until your stomach is 80 percent full"-may also be factors. Ironically, this healthy way of eating was born of hardship. Ushi Okushima grew up barefoot and poor; her family grew sweet potatoes, which formed the core of every meal. During World War II, when the men of the island joined the army, Ushi and her friend Setsuko fled to the center of the island with their children. "We experienced terrible hunger," Setsuko recalls.