Rice: Vegitables and Fruits: The Japanese diet for centuries has been rice, Especially for the peasants during the medieval era,Rice was introduced to Japan by a group of people Vegitables and Fruits were an important part of the known as the Yayoi roughly 2,000 years ago.diet.Sushi:Sushi was eaten during the medieval period.ice: Vegitables and Fruits: The Japanese diet for centuries has been rice, Especially for the peasants during the medieval era,Rice was introduced to Japan by a group of people Vegitables and Fruits were an important part of the known as the Yayoi roughly 2,000 years ago.