Tom Barber wrote:

"How does a high protein intake cause bone loss? In the process of
metabolizing protein, phosphoric and sulfuric acids are produced that must
first be buffered with calcium, an alkalinizing mineral, before they can be
excreted in the urine. Calcium is actually drawn out of the bones to reduce
or buffer these acid by-products of protein metabolism. If protein intake is
high and calcium intake is low or even moderate, a significant net loss of
calcium can result. When we consume the typical 95 grams of daily protein,
calcium is lost from the body, even on a very high calcium diet. Other
substances, taken in excess, also lead to calcium loss. For example,
phosphorus (often found in sodas), as well as caffeine, sugar, fats, salt
and alcohol can all become significant bone robbers. "


I was just reading Protein Power and they say this:

"A high protein (or adequate protein diet, as they put it) doesn't cause an
overall loss of calcium. The notion that high protein diets cause calcium
loss is a persistent rumor . . . that no amount of scientific research seems
to be able to dispel. Diets high in meat protein have been consumed for
millennia by people the world over without harm, so don't worry about
osteoporosis."