Although considered as separate parts of the whole, the body, mind and spirit are intricately linked, particularly when it comes to natural health philosophies.
How you view each element is really a matter of perception - the body can be seen purely as the biochemical part of us, and further considered as containing 'separate'aspects - such as physical bones, muscles and organs, the internal hormone mechanisms, the nutritional requirements for health and vitality. Others would view the body as a material representation of the state of the mind - matter like any other in the world that is first created in the mind.
The mind is also perceived in different ways - the decision maker, the link to something bigger than ourselves, the connection to all others (whereas the body is perceived as something separate), the seat of thought development. If you prescribe to the view that the mind has control over matter then the mind would have complete control over every aspect of the physical body (and this is seen in health with the placebo effect or perhaps in cases of seemingly illogical remissions from illness and the power of healing therapies or of prayer - which may also be spiritual).
When we take positive action to improve the diet or start regular exercise we usually enjoy an improved state of health and, in addition to physical changes we might see, we usually 'feel' better too - our thoughts change, perhaps we are more comfortable with ourselves, feel more confident, less stressed - they are aspects of the mind. Similarly, when we 'put our minds to it' or dig deep and harness our will power, we are often surprised at what we can do in physical terms - starting in the mind with a determination, or a feeling of not being satisfied with the status quo.
So examples of mind/body interaction are regularly experienced (although we might not always be conscious of those relationships).
What then of Spirit? I wouldn't even try to offer a definition so can only give my opinion - that the Spirit is fine as it is; it has no need of healing because it represents perfection. However, if we could align with the Spirit aspect of ourselves we would feel joyful. Our task then is to try and forge a greater bond with our spiritual aspect, and we all have different ways of doing that - you'll only know if you've achieved it through a feeling of joy. If your emotional health is compromised by feelings like anger, disappointment and fear, there are probably many paths back to health you could consider, but you might also benefit from forging a stronger spiritual connection. Some natural remedies can help; homeopathic and flower remedies for example work on emotional as well as physical health. Your connection or not to Spirit is also influenced by your perception of what it is - and that's an element of the mind.
So, with all this connected-ness where do you start to unravel your symptoms? Wherever you feel you can. Improve your diet, consider your level of exercise, meditate or be mindful.
When you take a positive step you feel an improvement; when you feel improvement you are encouraged to continue; so seize the moment and walk confidently down the path to better health today!