Protein powders are the culprit proteins
What is significant in the various studies of protein intake and bone density is that the studies which purported to show protein intake caused calcium loss were not conducted with real foods but with isolated amino acids and fractionated protein powders of the sort used by low-carb dieters and athletes. The reason why these amino acids and fat-free protein powders caused calcium loss while the fat meat diet did not is because protein, calcium, and minerals require the fat-soluble vitamins A and D for their assimilation and utilisation by the body. When protein is consumed without these factors it upsets the normal biochemistry of the body and mineral loss results.
[xviii] True vitamin A and full-complex vitamin D are only found in animal fats. Furthermore, saturated fats that are present with meat are essential for proper calcium deposition in the bones.[xix] It should be no surprise, therefore that vegan diets have been shown to place women at the greatest risk for osteoporosis.[xx] [xxi]