High intakes of skimmed milk, but not meat, increase serum IGF-I and IGFBP-3 in eight-year-old boys.

OBJECTIVE: To examine whether a high protein intake (PI) from either milk or meat, at a level often seen in late infancy, could increase s-IGF-I and s-IGF-I/s-IGFBP-3 in healthy, prepubertal children. IGF-I levels are positively associated with growth velocity in children and some studies suggest that a high animal PI can stimulate growth. During protein deprivation IGF-I decrease, but it is unknown whether a high PI can increase s-IGF-I in well-nourished children. DESIGN: In all, 24 8-y-old boys were asked to take either 1.5 l of skimmed milk (n = 12) or the same amount of protein as 250 g low fat meat (n = 12) daily for 7 days. The remaining diet they could choose freely. At baseline and after 7 days, anthropometrical variables were measured, diet was registered (3-day weighed records), and s-IGF-I and s-IGFBP-3 (RIA) were determined after fast. RESULTS: PI increased by 61% in the milk group to 4.0 g/kg/day (P <0.0001) and by 54% in the meat group to 3.8 g/kg/day (P = 0.001). The high milk intake increased s-IGF-I by 19% (P = 0.001) and s-IGF-I/s-IGFBP-3 by 13% (P <0.0001). There were no increases in the meat group. CONCLUSIONS: High intake of milk and not meat, increased concentrations of s-IGF-I and s-IGF-I/s-IGFBP-3 significantly. Compounds in milk and not a high PI as such seem to stimulate IGF-I. This might explain the positive effect of milk intake on growth seen in some studies.