High intake of milk, but not meat, decreases bone turnover in prepubertal boys after 7 days

Objective: To compare the short-term effect of a high milk and a high meat intake, identical in protein amount, on bone turnover during prepuberty. Setting: A University Department. Design and Subjects: From 28, randomly recruited, 8-year-old boys, first 14 were assigned to the milk group and next 14 to the meat group. In each group, 12 boys finished the dietary intervention. Intervention: Milk (1.51/day) and meat ( 250 g/d), both containing similar to 53 g of protein, were given together with the habitual diet for 7 days. At baseline and day-7, serum osteocalcin (s-OC), bone-specific alkaline phosphatase (s-BAP) and C-terminal telopeptides of type I collagen (s-CTX) were measured ( immunoassay) and dietary intake was estimated ( a 3-day weighted food record). Results: Baseline s-OC, s-BAP and s-CTX were not significantly different between the groups. After 7 days, the average protein intake increased in both groups by 47.5 g; the milk group had higher (P < 0.0001) calcium intake; s-OC and s-CTX decreased (P <= 0.04) in the milk group (-30.9%; -18.7%, respectively) compared with the meat group (+6.4%; -1.0%, respectively) and s-BAP decreased (P=0.06) both in the milk (-3.9%) and the meat group (-7.5%). Conclusions: At the equal protein intake, milk, but not meat, decreased bone turnover in prepubertal boys after 7 days. This effect was probably due to some milk-derived compounds, rather than to the total protein intake. Future studies should elucidate the mechanism(s) of milk-related decline of bone turnover and its relevance for peak bone mass during growth.