Simplify the following text for a Grade 5 native English-speaking person.
Original: Knut 's diet began with a bottle of baby formula mixed with cod liver oil every two hours , before graduating at the age of four months to a milk porridge mixed with cat food and vitamins .
Simplified: Knut 's food began with a bottle of baby milk mixed with cod liver oil every two hours . At four months old , he could eat milk porridge mixed with cat food and vitamins .