Kabayaki eel is very popular and a rich source of vitamins A and E, and omega-3 fatty acids.[3] A popular custom from the Edo period[4] calls for eating kabayaki during the summer to gain stamina,[4] especially on a particular mid-summer day called doyō-no ushi-no-hi[ja] (土用の丑の日?),[3][4] which can fall anywhere between July 18-August 8 each year.[5]