Q: [How can a person acquire kedusha through eating] if eating too much is unhealthy?
A: Absolutely it’s unhealthy. If people felt that they would be injuring themselves they probably would abstain. What don’t people do for kedusha (sanctity); don’t people fast for kedusha? So they also eat for kedusha. There are two considerations, what’s good for your body, what’s good for your soul.
The poor body complains, “I have to suffer because you want to improve your character?”"
In general you have to try to strike a happy medium and do what’s good for both. Sometimes, however, people fast in order to improve their character,and their poor body complains, “I have to suffer because you want to improve your character?” So you ask your body please cooperate with me because I have to do something for my neshama (soul).
If you have to eat a seudas mitzvah like on Pesach night when it’s a mitzvah to eat, even though you don’t like some of the things, you would prefer to have other things, your body cooperates in order to help you achieve the mitzvah. The truth is the body gains kedusha thereby too, and the body is also no loser. — Starting the Climb to Kedushah (#518)