Contrary to accepted wisdom, high protein intake does not seem to be harmful to mineralization of bone, according to Seattle-based researchers reporting in the American Journal of Clinical Nutriton. Mineralization of bone is important because higher bone mineral content generally translates to lower risk of fractures.
A consistent criticism of low-carbohydrate diets in the past is that they are detrimental to bone health. How so? If you reduce carb consumption, you have to replace at least some of the calories with either fat or protein. Some low-carb diets lean towards higher protein content, others towards higher fat, still others increase both fat and protein. The building blocks of proteins are amino acids, and some amino acids are acidic. Acid-rich biochemical states may promote removal of calcium from bone and, ultimately, loss of that calcium in urine. The calcium-poor bones are more prone to fracture.
If that theory is correct, women eating greater amounts of protein should demonstrate lower bone mineralization. [The primary bone minerals are calcium and phosphorus.]
Investigators tested the theory in 560 women aged 14 to 40 by measuring bone mineral density (via DEXA scans) over two or three years and monitoring food consumption via yearly questionnaires. This was an observational study, not interventional.
They found that bone mineral density had nothing to do with protein consumption. Higher protein intake was not associated with lower bone density.
Women in the low-protein group ate 52 g of protein daily, compared to 63 g in the medium group and 77 g in the high-protein tertile. As best I can tell, the low-protein third of participants ate 12% of total calories as protein, compared to 20% in the high-protein third. [Study authors could have put this in the appropriate table, but, mysteriously, opted against that.]
We can’t tell from this study whether these findings apply to protein intakes outside this range, to men, or to women older than 40. To their credit, the study authors review much of the pertinent literature and note that research in this area produces results all over the map. To me, this suggests that the association between dietary protein and bone mineralization in the general population is weak, if not nonexistent.
Looks like you can stop worrying so much about hurting your bones if you’re on a low-carb, high-protein diet.
Reference: Beasley, J., Ichikawa, L., Ange, B., Spangler, L., LaCroix, A., Ott, S., & Scholes, D. (2010). Is protein intake associated with bone mineral density in young women? American Journal of Clinical Nutrition, 91 (5), 1311-1316 DOI: 10.3945/ajcn.2009.28728