Studies into the effects of high animal-protein intake compared with vegetarianism on the risk of osteoporosis have produced confusing and contradictory findings. This may be in part because dietary protein has a paradoxical effect on bones.
On the one hand, protein increases the loss of calcium in urine (J Lab Clin Med, 1994; 124: 15-6; J Nutr, 1990; 120: 134-6), which should increase the risk of osteoporosis. But on the other hand, normal bone formation requires adequate dietary protein, and a low dietary protein intake has been associated with low bone mineral density, one indicator of bone strength (Calcif Tissue Int, 2000; 66: 313).
Unfortunately, the line between too much and too little protein remains elusive. The key, as always, seems to be moderation in all things. The wisest course may be to ensure that you have a widely varied, organic wholefood diet that includes plenty of fruits and green leafy vegetables.