While patients tend to assume that boosting their calcium intake will ensure strong bones, research clearly shows that calcium intake is only part of the issue and that simply increasing calcium intake is an inadequate strategy. No less important is reducing calcium losses. The loss of bone mineral probably results from a combination of genetics and dietary and lifestyle factors, particularly the intake of animal protein, salt, and possibly caffeine, along with tobacco use, physical inactivity, and lack of sun exposure. Animal protein tends to leach calcium from the bones, leading to its excretion in the urine. Animal proteins are high in sulfur-containing amino acids, especially cystine and methionine.
Sulfur is converted to sulfate, which tends to acidify the blood.
During the process of neutralizing this acid, bone dissolves into the bloodstream and filters through the kidneys into the urine. Meats and eggs contain two to five times more of these sulfur-containing amino acids than are found in plant foods. 3 International comparisons show a strong positive relationship between animal protein intake and fracture rates. Such comparisons generally do not take other lifestyle factors, such as exercise, into account. Nonetheless, their findings are supported by clinical studies showing that high protein intakes aggravate calcium losses.