This may seem somewhat outdated now but it's still fresh and could be a good intro to what acid-alkaline means. It was actually an introduction for me: I had not known about PH before (Potential for Hydrogen).
I like how this book, about food intake, is scientific in nature and is chemistry-based. Science kinda rocks! Susan explains the 0 to 14 levels of PH; pointing out that 7 is the median: what is under 7.0 is mostly acid and what is above 7.0 is leaning more toward alkaline.
While reading this book, I started to look into PH levels in water and was dismayed to find out that not all water bottles are created equal. Some have HIGHER Ph levels, and probably celebs who know about PH levels would root for the fancier water bottles. This was disturbing as it got me thinking about the inequality in the world, and how some people not only do not have access to high PH levels of water but perhaps no clean water at all.
In this respect, this book is timely now that people are (hopefully) becoming more environmentally conscious and considering shifting away from making the earth more toxic than it - which is directly linked with the body toxicity. Animal products, after all, are all acidic, and poultry are HIGHLY acidic.
With that being said, a vegan diet, which is clearly preferable, is also not free from acid. White bread and cakes at large after all, are acidic, not to mention alcohol... and coffee! Having all this in mind, it makes sense: the urine is perhaps one of the ways demonstrating the science behind the PH levels. When doctors say "drink more water," this book explains the science backing this up. However, it's not JUST the water - it's also the fruits and vegetables (sweet potatoes and onions are among those which have high alkaline) and it's also how one can pay attention to how the over-use of caffeine and alcohol consumption can bring alkaline down while the acid goes up. It's fun to explore how these things work.
Definitely an informative book with clear charts referencing the foods and where they fall under the acid/alkaline intensity.