American Journal of Clinical Nutrition, Vol. 82, No. 5, 1107-1114, November 2005 © 2005 American Society for Clinical Nutrition

Ute Alexy, Thomas Remer, Friedrich Manz, Christina M Neu and Eckhard Schoenau

1 From the Research Institute of Child Nutrition, Dortmund, Germany (UA, TR, and FM), and the Children's Hospital, University of Cologne, Cologne, Germany (CMN and ES)

Background: Protein and alkalizing minerals are increasingly described as playing a major role in influencing bone status, not only in the elderly but also in children and adolescents.

Objective: We examined whether the long-term dietary protein intake and diet net acid load are associated with bone status in children.

Design: In a prospective study design in 229 healthy children and adolescents aged 6–18 y, long-term dietary intakes were calculated from 3-d weighed dietary records that were collected yearly over the 4-y period before a one-time bone analysis. Dietary acid load was characterized as potential renal acid load (PRAL) by using an algorithm including dietary protein, phosphorus, magnesium, and potassium. Proximal forearm bone variables were measured by peripheral quantitative computed tomography.

Results: After adjustment for age, sex, and energy intake and control for forearm muscularity, BMI, growth velocity, and pubertal development, we observed that long-term dietary protein intake was significantly positively associated with periosteal circumference (P < 0.01), which reflected bone modeling, and with cortical area (P < 0.001), bone mineral content (P < 0.01), and polar strength strain index (P < 0.0001), which reflected a combination of modeling and remodeling. Children with a higher dietary PRAL had significantly less cortical area (P < 0.05) and bone mineral content (P < 0.01). Long-term calcium intake had no significant effect on any bone variable.

Conclusions: Long-term dietary protein intake appears to act anabolically on diaphyseal bone strength during growth, and this may be negated, at least partly, if dietary PRAL is high, ie, if the intake of alkalizing minerals is low.