The human body is part of nature, as we discussed before as a microcosm of the universe, and when it runs perfectly, as it was designed to run, it can be perfectly healthy. But we repeatedly interfere. Nature has set us up with all the equipment we need to be perfectly healthy.
Health is our natural state, and ill health is unnatural.
Every day our systems are exposed to literally millions of bacteria, viruses, allergens, even carcinogens, and yet our immune system has the intelligence and skill to deal with all those invaders and keep us healthy. However, when stress, inadequate nutrition, or just fatigue weaken the immune system, those same invaders may produce disease. Every second the body is adjusting to countless thousands of changing parameters, keeping us in homeostatic balance. No matter what comes along to upset the balance, the body knows its own nature, knows what ideal temperature it should be and the correct chemistry it needs to maintain, and keeps referring back to that blueprint to maintain proper balance.