From the book Advice:
Rabbi Nachman: ADVICE (LIKUTEY ETZOT) by Rabbi Nathan of Breslov

Eating #1
If the food a person eats is pure in accordance with the dietary laws and he eats it with dignity, without swallowing it hurriedly, the powers of his mind will be restored and grow and his foolishness will be subdued. But if he eats like a glutton, then he will be overwhelmed by foolishness. He will lose his intelligence and the light of the Tzaddik will be concealed from him. He will no longer be able to learn the love and fear of God from the Tzaddik (17: 2,3).