The most important influences on your health are the things that you do constantly. No matter how intensely you try to correct bad health with crash diets or harsh exercise in the end your habits shall overcome them and destroy your body. The good habits you need are Posture and breathing. You are always sitting or standing if you are at work or leisure, and you breath until you die.
Posture is very important because if it is bad your body will tire out muscles and systems that are not meant to be placed in bad positions for long periods of time. Bad posture can inhibit good blood circulation, which will keep vital nutrients from getting where they are needed, and it will also allow waste to settle in areas without being flushed by the blood. This can lead to disease conditions.
Breathing of course places oxygen into the blood which is vital for the body to function properly, it also removes waste gases on the exhale. Proper breathing energizes the body and allows it to handle stress much better than if you just breath “naturally”.
Proper posture is keeping the spine upright so that it is not hunched over itself. The body should be tilted very slightly forward in standing or sitting, but in a straight line up and down. Proper breathing is slower breathing that is deep in breath. Typically you want to breath in and out slowly, with a pause of a few seconds in between.
Obviously this takes some thought to do, and you will forget often at first. Whenever it comes to mind just do it again. Do not beat yourself up over forgetting, just endeavor to remember more.
These are simple steps to better health. They are constant and will have more impact in the long run than either diet or exercise. Continue in them and your body shall remain strong into old age unless of course you have an accident. Hope this helps.