Previous studies show that high intakes of animal protein can lead to bone loss. This five-year study in the British Journal of Nutrition looked at the diets of 757 girls in Beijing, China. Some of the group were given cow’s milk for the first two years. Results showed that while calcium intake improved bone health, animal protein (especially from meat and eggs) reduced bone density. Plant protein did not have this harmful effect.
Zhang et al., 2010. The association between dietary protein intake and bone mass accretion in pubertal girls with low calcium intakes. British Journal Nutrition. 103 (5) 714-723.