I was just commenting to another writer about this "health is when you punch the body and it punches back harder" effect (aka "that which doesn't kill you makes you stronger"). This theory has been ascribed to the efficacy of chemotherapy (which allegedly rallies your own immune system), and famously exercise. There is some evidence that flavonoids and polyphenols may be good for us using this principle also. mTOR inhibitors probably also use this effect.