Exploring healthy eating advice

I am an avid reader of books which advise on healthy eating and healthy lifestyles, along with pretty consistent online research on the same topic. However, I was pretty startled to read about claims as to the extent to which the ph of your body affects your health. I was aware that an alkaline digestive system is a desirable thing, but reading about the claims that having your whole body in an alkaline state totally discourages cancer from flourishing was a new concept for me. Having also recently read that sugar encourages cancer cells in the body to replicate - and ingesting simple carbs makes your system acidic apparently - the two theories seem to complement each other. Also, stress can very quickly turn your system from alkaline to acidic - in as little as five minutes! All very interesting, but are these theories sustained by good research and lots of empirical evidence? As usual, it is very difficult to tell how well founded some of these theories are, and if the paranoia about the efforts made by big business to suppress some of these findings has any basis in reality. However, if these claims have even a small grain of truth then they should be explored by everyone to see if making changes to diet can improve health and longevity - not just to tackle obesity, but to address other major illnesses such as arthritis, diabetes and cancer.