Wheat bran supplementation does not affect biochemical markers of bone turnover in young adult women with recommended calcium intake

We investigated the effect of wheat bran on biochemical indicators of Ca and bone metabolism in nineteen healthy women, aged 25.5 (sE 0.9) years. Subjects received six wheat bran biscuits or six white flour biscuits per day for a period of 4 weeks (crossover). Wheat bran consumption increased fibre intake from 17.7 (sE 1.3) to 29.6 (sE 1.3) g/d (7 d food record) and enhanced P intake from 1225 (sE 59) mg/d to 1663 (sE 65) mg/d; P < 0.001. Mean daily Ca intake during wheat bran consumption (1110 (sE 82) mg/d) significantly (P = 0.008) exceeded Ca ingestion during the white hour period (955 (sE 67) mg/d). Wheat bran increased the number of defecations per week from 7.9 (sE 0.8) to 12.2 (sE 1.4) (P = 0.0018). Urinary Ca excretion over 24 h significantly (P = 0.021) decreased from 473 (sE 53) mu mol/mmol creatinine (control period) to 339 (sE 37) mu mol/mmol creatinine (wheat bran period). Serum 25-hydroxyvitamin D, 2 h fasting urinary Ca/creatinine excretions and 24 h urinary P excretion remained constant. No differences in serum levels of carboxy-terminal propeptide of type I procollagen (biomarker of bone formation) or in 2 h fasting urinary hydroxyproline/creatinine excretions (biomarker of bone resorption) were observed at the end of the two cycles of dietary supplementation. We conclude that a high fibre intake of approximately 30 g/d has no significant adverse effects on bone turnover in subjects with Ca intakes above 1000 mg/d and that the reduction in 24 h urinary Ca excretion is most probably the result of an adaptation process, induced by a decrease in net absorbed Ca.