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 However, not all protein is created equalNot all proteins have the same effect on increasing calcium loss through the kidneys. When animal protein is replaced with soy protein, much less calcium is lost 6 . A study of middle aged and elderly women in China with various dietary patterns, found that urinary calcium excretion increased with a higher intake of animal protein (including dairy) and nondairy animal protein but decreased with a higher plant-protein intake 7 . A study of Japanese men and women, aged 20-79 years, confirmed that excess protein, particularly the type rich in sulphur-containing amino acids (such as from meat) may increase calcium loss in the urine 8 . Studies have also found that the intake of animal protein as compared to plant derived protein, is linked with an increased risk of fractures. Researchers at the Yale University School of Medicine examined 34 scientific studies from 16 countries around the world, and found that as animal protein intake increases, so do female hip fracture rates 9 . Scientists at Wayne State University, Detroit found that although a twofold increase in protein intake (at constant levels of calcium and phosphorus intake) causes a 50% increase in the amount of calcium lost in the urine, a soy protein-based diet is able to maintain calcium balance under these conditions 10 . This is thought to be due to the lower content of sulphur amino acids found in soy protein as compared to animal proteins. Sulphate, produced by the metabolism of sulphur containing amino acids, is thought to have a negative effect on the reabsorption of calcium by the kidneys back into the blood stream.
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