This is a topic I've followed with interest for as long as I've been studying nutrition.  I do believe that Americans eat a diet that acidifies the body and that an acid body is home for disease - all types, osteoporosis, arthritis, and even cancer, at the top of the list.
 
How to break this down and give a good explanation without getting overly complicated has been my challenge, especially because Western medicine, until quite recently, has debunked the theory that you can affect the pH of the blood by diet.
 
The theory:  At the end of digestion nutrients enter the bloodstream.  All food goes through this process of digestion and has a residue ("ash") that has a pH score.  The score will be between 1 (most acidic) and 14 (most alkaline).
So, when we talk about acid vs alkaline foods, what we really mean is:  foods that produce acid or alkaline residue at the end.  The blood must stay within a pretty tight range, as close to neutral (pH 7) as possible or death will be the end result (acidosis, alkalosis) To do this, the body will go to extremes to keep the blood balanced at or near neutral ph of 7.  It actually prefers to hum at 7.3- 7.4, slightly alkaline.  If our food choices over and over again tax the blood's ability to stay neutral, it will pull calcium and other minerals our of our bones to keep the balance.  The body's wisdom is this:  osteoporosis is better than death :-)
 
But finally this debate has hit the "mainstream."  In the past 3 months, I've read articles in the NYTimes, LATimes and Wall Street Journal, that have reported on mega studies regarding osteoporosis and intake of calcium from dairy products (ie, "a body needs milk" ads)  All the research, including those combined in the book called:  The China Study by T Colin Campbell over a 50 year period, gathering data on hundreds of thousands of people from cultures around the world, are pointing toward the conclusion that taking Calcium doesn't ward off osteoporosis.  In fact the countries with highest milk and meat intake have the highest rate of bone fragility, from osteopoenia to osteoporosis.  And that the cultures who consume the highest amount of plant foods have less disease of all kinds.
 
The conclusion by doctors practicing nutritional medicine have long touted the idea that the human diet should be about 70% alkaline residue and no more than 30% acid residue.  That type of diet will keep the blood happy at a balanced ph of 7 without effort.  If the diet has too many "acid producing" foods, then the body must work very hard to maintain that balance.
 
Tomorrow's email  will explain this chemistry further (I talked to an MD and a chemist who understands digestion) to make sure I got it right.
But let me tease you a bit:   bread, cheese and meats have an extremely high acid residue and lemon juice  (not lemonade!) is highly alkalizing.......
 
mary anne