Protein intake and calcium absorption – Potential role of the calcium sensor receptor

Dietary protein induces calcium excretion but the source of this calcium is unclear. Evidence from short-term studies indicates that protein promotes bone resorption, but many epidemiologic studies do not corroborate this. Evidence is also mixed on whether protein promotes calcium absorption. Studies in animal models suggest that the aromatic amino acid components of protein, but not the branched-chain amino acids, may activate calcium sensor receptors in the gut and increase gastric acid production. The latter could enhance calcium absorption. We compared the impact of aromatic and branched-chain amino acids on changes in calcium excretion and on an index of calcium absorption in 30 healthy older men and women. A 5-fold increase in aromatic amino acid intake induced a greater increase in calcium excretion, calcium absorption, and serum IGF-1 than did a similar increase in branched-chain amino acids. These findings are consistent with the concept that the calcium sensor receptor mediates selected effects of dietary protein on calcium metabolism.