The Laws of Prayer /The Amidah (87)

1. Even though it is forbidden to eat or drink before praying, a man who is extremely hungry or thirsty is considered like an ill person and the law is as follows: if he can concentrate on his praying without eating or drinking, he should pray without eating or drinking. If, however, he is unable to concentrate, he is allowed to eat and drink before praying so that he can pray with full concentration. (Mishne Berurah 89)

2. Even a person who started eating at a permissible time-before sunrise, must interrupt and stop eating as soon as the sun has risen in order to pray. (ibid)