In some cases it's a matter of vibrations and stuff that is not "physical" like emotional problems, etc...i mean when someone has a heartbreak that is not solved and caused depression, anxiety etc it could manifest in the physical with a illness (cancer or other stuff). Mental and emotional health is important not just eating healthy and doing some sort of excercise, avoid smoking, heavy drugs and alchool, because if there is no mental stability and there are issues in family, you are overstressed from your job or school and other issues our body could resent it and get ill. I see people that hasn't a super healthy life (they smoke or eat not super controlled and stuff) that live without illnesses because they are happier, their mind is more stable or at least any mental illness is controlled and not spiralling out of control and have what they desire. Being super healthy and super fixated into it isn't always a good thing if you ignore the mind and spirit. I don't mean "hey lets do all the unhealthy stuff!", i mean our emotional side is important as taking care of our body without overstress and obsess yourself to get super healthy, there is no need to eat only veggies and fruits and no carbs at all and several hours of gym to be healthy if you don't want it. Just the basics are what you need in my opinion.