Western diets are net acid-producing, based on their general characteristics of containing excessive amounts of grains in relation to their content of fruits and vegetables. The continuous consumption of acid-producing diets is countered by the renal excretion of the excess acid. However, when renal excretion is not adequate, as is the case in many older adults with mildly and moderately impaired renal function, other adaptations are employed to preserve neutrality. In adults who are unable to excrete the daily dietary acid load, the excess acid is buffered by bone. The mechanisms by which hydrogen ions affect bone have been well defined. Current evidence also indicates a role for muscle in preserving neutrality; however, the mechanism(s) by which this occurs have not been directly demonstrated. The evidence supporting the role of bone and muscle in defending against the development of frank metabolic acidosis are reviewed herein. This evidence stems from observational studies and randomized, controlled clinical trials. Gaps in the evidence that would be useful to fill are also indicated.