These acids are ultimately excreted by the kidneys, but as we age, our kidneys don't function so well. If the kidneys can't keep up with our appetite, the bones step in and absorb the excess acid. That's good in the short term, but in the process the bones surrender calcium, phosphorus, sodium, and everything they should be keeping to stay strong. As much as 30 percent of post-menopausal white women, the group at greatest risk, have osteoporosis. Protein generates more acid than other foods, and the proteins in red meat generate more acid than those in fish or poultry.
Vegetable proteins give rise to the least amount of acid.