All I know is I am sick way less often than when I lived with money. Yes, I've sometimes gotten a little queezy from being careless, but less so than when I lived a moneyed, sterile life, I can asure you. I've been sick & vomiting 3 times these past 8 years living moneyless. Ironically, the first two times were not from my usual dumpster dine-outs, but the first time when a friend had me over to her house for dinner and the second time when a friend bought me food at a restaurant. The third time I got sick and vomited was when I carelessly ate a poison cactus.
The immune system is like your muscles. If you don't excercise it, it will atrophy, and you will get sick more often. If you live too cleanly, you will get weak and sick more often. This should be common sense.
I never, ever get colds & flu when I live outdoors, even in below-freezing weather. The only times I've gotten colds since I started living this way in 2000 has been when I house-sit. Constantly going from indoors to outdoors, from warm to cold and cold to warm, as well as being in stale indoor air, is hard on the body.
There is nothing more detrimental to health than worrying about health. I'm not talking about thinking and caring about health, but worrying about health.