Our digestion corresponds to our determination. When you are determined, you can usually maintain your health, small things cannot hinder you. But when your spirit is weak you will get sick even if you eat good food. I mean natural food. Nevertheless our spirit should be strong and stable so we can digest our food properly and distribute the nutrients to our body.
Posture is important as well.
If you have bad posture it will impair your health. It is important to keep good posture, God created man to live in this way. Some people's backs become curved when they become old. This comes from bad posture or sleeping in a bad position. So we must keep good posture in order to maintain good health as God intended.