Bone is approximately 30 percent organic matrix, primarily Type I collagen, and 70 percent mineral, primarily hydroxyapatite. The collagen matrix is what gives bone its flexibility and fracture resistance; the mineral provides hardness and compressive strength. Both require adequate nutrition to be maintained. While calcium and Vitamin D are widely recognised as bone nutrients, the contribution of protein to bone health is consistently underappreciated in clinical practice.
The Evidence on Protein and Fracture Risk
A review by Bonjour et al. synthesised the evidence on dietary protein and bone health and concluded that higher protein intake was positively associated with bone mineral density across multiple population studies. A meta-analysis of 20 prospective cohort studies found that higher total protein intake was associated with a 6 to 16 percent reduction in hip fracture risk. The effect was present for both animal and plant protein, though animal protein showed stronger associations, likely due to higher leucine content and bioavailability.
The Protein-Calcium Interaction
Earlier research suggested that high protein intake increased urinary calcium losses and might harm bone. Subsequent research has shown that this effect is small and offset by protein's positive effects on IGF-1 production, calcium absorption, and bone formation. The net effect of adequate protein intake on bone in adults who also consume adequate calcium is positive, not negative. The concern about protein and bone was based on studies in populations with borderline calcium intake, not on populations consuming adequate calcium.
Sources
- Bonjour, J.P. (2011). Protein intake and bone health. International Journal for Vitamin and Nutrition Research, 81(2-3), 134-142.
- Mangano, K.M., et al. (2017). Dietary protein is associated with musculoskeletal health independently of dietary pattern. Journal of Nutrition, 147(9), 1705-1713.
- Darling, A.L., et al. (2009). Dietary protein and bone health: a systematic review and meta-analysis. American Journal of Clinical Nutrition, 90(6), 1674-1692.