Keeping ourselves in good health requires, first of all, visiting periodically a doctor for routine checks up and/or when we have, or we suspect we have, any symptom of a possible disease.
Maintaining a good health also involves the discipline of keeping ourselves away from bad habits. For example: smoking cigarettes. If I smoke I cannot expect the doctor to perform a miraculous treatment to my lungs. Additionally, it will be a big irony praying to haShem to protect me from a lung disease, while I'm still smoking.
Besides avoiding bad habits we also need to acquire healthy "protective" habits. These Segulot for preventing diseases were best formulated by haRambam or Maimonides.
Maimonides, who apart from being a rabbi was also a famous physician, wrote a whole chapter on preventive medicine in Mishne Tora, Hilkhot De'ot, chapter 4. In 4:21 he explicitly clarifies that all the principles exposed in this chapter are applicable exclusively for a healthy individual, not for a sick person, who would obviously require a customize diet and medical treatment. Anticipating the modern concept of 'preventive medicine' by eight centuries Maimonides dealt with: working out, sleeping habits, sexual life, hygiene, etc.
He also wrote extensively on a correct diet.
4:1 "...Maintaining a healthy and sound body is among the ways of God... one must avoid that which harms the body and accustom himself to that which is healthful and helps the body becomes stronger".
4:2 ".. a person should not eat until his stomach is full. He should stop eating approximately at three quarters of his full satisfaction"
4:15 "...overeating (akhila gasa) is like poison to anyone's body and it is the main source of all illness".
4:1 "Do not eat unless you're hungry".
Click here to download Hilhkot De'ot Chapter 4.
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