good appetite and good bowel movements
A set phrase describing the ideal state of eating well and having regular, healthy bowel movements, often used in health contexts.
健康の基本は快食快便です。
The foundation of health is good appetite and good bowel movements.
快食快便を心がけています。
I try to maintain good appetite and regular bowel movements.
A four-character compound combining 快食 (good appetite) and 快便 (good bowel movements). The exact origin is uncertain, but it is a modern health-related phrase.