Effect of milk proteins on linear growth and IGF variables in overweight adolescents

ObjectiveMilk may stimulate growth acting via insulin-like growth factor-I (IGF-I) secretion but the effect in adolescents is less examined. This study investigates the effect of milk proteins on linear growth, IGF-I, IGF binding protein-3 (IGFBP-3) and IGF-I/IGFBP-3 ratio in overweight adolescents.DesignThe trial included 193 overweight adolescents aged 12–15 years. They were randomized to drink 1 L/day of: skimmed milk, whey, casein or water for 12 weeks; all milk-based drinks contained 35 g protein/L. A subgroup of 32 adolescents was examined 12 weeks before they were randomized into the groups and started the intervention (pre-test control group). Examinations included anthropometry, diet registration and blood samples which were analyzed for IGF-I and IGFBP-3 by chemiluminescence methods. The effects of milk-based drinks on linear growth, IGF-I, IGFBP-3 and IGF-I availability, calculated as the IGF-I/IGFBP-3 ratio, were compared with baseline, the pre-test control group and water.ResultsIGF-I increased with skimmed milk (P = 0.015) and tended to increase with casein (P = 0.075) compared to the pre-test control group. IGFBP-3 but not IGF-I increased with skimmed milk (P = 0.006) and casein (P = 0.001) compared to water. There was no difference in height or height Z-score for any of the milk-based test drink groups compared to water or compared to the pre-test control group. However, height Z-score decreased within the whey group.ConclusionsSkimmed milk and casein may have a stimulating effect on the IGF-I system whereas there was no positive effect on height in overweight adolescents during this 12 week intervention.