谓致病之由，多在于饮食不慎a poor diet leads to illness; illness find its way in through the mouth

• 病从口入，祸从口出。

  Illness comes in through the mouth, and trouble comes out through the mouth.

• 病从口入，所以现代人非常讲究养生，养生也成为一门新学问。

  A poor diet can lead to illness, so people nowadays pay great attention to staying healthy, which has become a science in its own right.