Proteins are essential for growth, this is why many here will use beefheart and blackworms.
Blood worms are like candies...Very poor in protein (I think around 13%) but they are a great way to stimulate your fishes appetite once in a while.
Blackworms: VERY rich in proteins (60%)
BUT live blackworms can grow your discus in a great way but also kill them in an even faster way (they can carry diseases...been there, done that). A safer way is to go with freeze dried blackworms (sold on this forum), which wont make too much of a mess and don't carry diseases.