According to the hadith of Abu Dharr (may Allah be pleased with him), the Prophet (peace and blessings of Allah be upon him) said concerning the water of Zamzam, "It is a blessing, and it is food that satisfies." (Reported by Muslim, 4/1922).
Al-Tayaalisi (61) added, in a version that he narrated:
"and a cure for the sick." I.e., drinking the water of Zamzam means that a person does not need to eat, and it will cure his sickness - but this is when he drinks it with faith and sincerity, as proven in the hadith of Abu Dharr al-Ghifari who stayed in Makkah for a month without any nourishment except Zamzam water.