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There is evidence that the consumption of diets containing large amounts of animal protein is associated with low bone mineral content (BMC). Mazess and Mather (1974, 1975) observed that in Eskimos, whose diets consisted chiefly of meat and provided about 200 g of animal protein per day, bone loss occurred earlier in life and was of greater magnitude than in Caucasians in the U.S.A. An explanation for these observations is based on findings that the higher content of sulfur-containing amino acids in animal as compared to plant proteins results in a greater production of metabolic acid (Halperin and Jungas, 1983; Breslau et al.,1988) and higher net excretion of urinary acid. This increased acid load is buffered by calcium which in individuals with marginal or negative calcium balance is made available by the dissolution of bone (Allen et al., 1979; Schuette et al., 1980; Bushinsky, 1989). Because foods that have a high protein content also tend to be high in phosphorus, the calciuretic effect of a diet high in protein may be ameliorated by the concomitant presence of phosphorus. There is evidence that increased phosporus intake depresses serum calcium levels and stimulates the synthesis of parathyroid hormone which leads to increased reabsorption of calcium by the renal tubules (Yuen et al., 1984). |
