Why is it that some people suddenly cure themselves, while others fall to some terrible disease? Most would say that there are so many variables that no one can predict why, but all admit it happens. Okay, this all makes sense, still, we know, that one can destroy their health through hypochondriac behavior, or work with the system to eat right, exercise and keep everything doing its job right.
Some say that since the human body is really made up of more bacterial DNA than human DNA code that it is important to achieve a compromise with this complex biosystem to stay healthy. In other words, allow the bacteria to fulfill its needs, and thus keep the system able to achieve its goals too.
Rather than fight it, make a deal with it, everyone wins. The win / win includes allowing "you" or what you think is "you" to fulfill its pursuit of happiness and health, while the bacteria gets its basic needs so that all the cells end up vibrating at the right frequency providing a happy environment to excel.
Now, if we are to take such a theory literally, we must also think positive for better health, which is kind of like the saying; "We become what we think."
It might also be that the mind can over-ride the bacteria in the body to command it to do what's best, and that the mind will reward the entire symbiotic system with chemical commands, that is in the best interest of the entire system. Of course, this assumes one believes that a complex species like a human being is really more bacteria, than it is actually human. You decide.