One very important factor that impacts calcium balance and bone strength has received little attention. Human beings evolved on a diet consisting largely of fruits and vegetables supplemented with modest amounts of animal products. The metabolic residue from fruits and vegetables is highly alkaline due largely to their high potassium content and less so to their calcium and magnesium content. Foods of animal origin yield an acidic residue.

In modern diets, calories from fruits and vegetables have been displaced by grains, which yield a modestly acid residue. There has also been an increased consumption of animal products, some of which are metabolically very acid forming. As a result, the urine of modern humans is generally acidic, whereas that of our ancient ancestors was likely alkaline. Aging lowers the body’s ability to deal with more acidity.A recent study by Dr. Dawson-Hughes examined the impact of adding sodium or potassium bicarbonate supplements to a typical modern diet in 171 subjects age 50 and older. This study found not only a decrease in calcium lost in the urine in response to the bicarbonate supplements but also a reduction in urinary N-telopeptide – a marker for more rapid bone breakdown. Sodium bicarbonate and potassium bicarbonate increase the alkalinity of blood and urine. Dr. Dawson-Hughes concluded that alkalinizing the urine “… had a favorable effect on bone resorption and calcium excretion. This suggests that increasing the alkali content of the diet may attenuate bone loss in healthy older adults.”1 Bottom Line: The evidence is more than sufficient to encourage Americans to consume more fruits and vegetables and cut way back on foods like meats, eggs, and cheeses that acidify the blood and urine. Those with already weakened bones should replace some of the grain products in their diets with potatoes and yams. While salt has little impact on acid-base balance it increases calcium loss and is best limited in those with thinning bones.  By James J. Kenney, PhD, RD, FACN 1. J Clin Metab. 2009;94:96-102