الصيام
Voluntary and obligatory abstention from food and drink from dawn to sunset, described as beneficial for the body alongside its spiritual purpose.
صُومُوا تَصِحُّوا
“Fast, and you will become healthy.” (meaning, not a literal translation)
Ibn al-Qayyim discusses periodic fasting as giving the digestive organs rest, likening it to how rest benefits any organ subject to continuous work.