Protein and Bone Health
Associate Professor, Department of Allied Health Sciences, University of Connecticut
While calcium and vitamin D are well recognized for their role in the prevention of osteoporosis, the impact of dietary protein on bone health is less well understood. A well-accepted hypothesis holds that high-protein diets are possibly/potentially detrimental to bone because they increase urinary calcium. But that’s not the whole story...
The impact of protein on bone
Most epidemiological studies with bone mineral density or rates of bone loss as the principal outcome indicate that high-protein diets are associated with higher bone mineral density and slower rates of bone loss. Our research group designed a study to compare the short-term effects of high (2.1 g/kg) and moderate (1 g/kg) protein diets on calcium absorption and kinetic measures of bone turnover in healthy women (n=13).1 Although there was greater urinary calcium excretion in the higher protein diet, bone resorption was not higher in that group nor was there a difference in bone formation or bone balance between the two groups. The increase in urinary calcium excretion was due not to bone resorption, but to increased intestinal calcium absorption. Indeed, almost 90% of the urinary calcium could be traced to absorbed calcium. Similarly, the proportion of urinary calcium originating from bone was somewhat lower in the high-protein group, suggesting a trend towards reduced bone turnover.1
Further studies suggest that the source of the protein matters. Our team randomized 20 healthy women to diets containing high or low levels of protein (2.1 vs. 0.7 g/kg) of two major types (soy vs. animal). All subjects consumed all four experimental diets.2 Consistent with our previous work, the high-protein diets increased 24-hour urinary calcium, regardless of protein source. However, in a subset of subjects, intestinal calcium absorption tended to be lower with the soy-based rather than the animal-based diet, thereby resulting in a significant rise in PTH, a hormone that can accelerate skeletal resorption.2 These data suggest that when soy proteins are substituted for animal proteins, the bioavailability of calcium declines, at least acutely.
Milk products are an ideal source of high-quality protein and contain other bone-building nutrients such as calcium, vitamin D, potassium, phosphorous, magnesium, zinc, vitamin B12, and vitamin K.
Adequate calcium and vitamin D are essential for optimal bone health.
A high-protein diet is beneficial to bone, particularly when calcium and vitamin D intake is limited.
High protein diets are associated with decreased bone loss and fractures.
Adults with limited protein intake are at high risk for bone loss and fractures.
Soy protein does not appear to be advantageous to the skeleton.
- Kerstetter JE et al. The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women. J Clin Endocrinol Metab 2005;90: 26–31.
- Kerstetter JE et al. Meat and soy protein affect calcium homeostasis in healthy women. J Nutr 2006;136:1890-1895.