Without food, how could he grow stronger?
All the elites in the tribe ate desolate beast meat daily. It gave large amounts of high quality energy, and was worlds apart from the whole grain porridge he ate!
Yi Yun knew that if he starved himself for prolonged periods, it would cause adverse harm to his body. He was still in his growing years, and only had a tremendous improvement in his body due to having been rejuvenated through the Marrow Cleansing.