Background: Animal models have shown that insulin-like growth factor I (IGF-I) may mediate protein-induced kidney growth. Our aim was to analyze the effect of IGF-I on protein-induced kidney growth in healthy infants.
Methods: This is a secondary analysis of a randomized trial that compared growth of infants fed with a higher-protein (HP) (n = 169) vs. lower-protein (LP) (n = 182) formula (in the first year of life). Outcome measures were anthropometric parameters, kidney volume (cm(3)), and total and free IGF-I (ng/ml).
Results: The highest levels of total and free IGF-I were found in the HP group. Both parameters correlated significantly with BMI z-score (r = 0.229, P < 0.001 and r = 0.223, P < 0.001, respectively), kidney volume (r = 0.115, P = 0.006 and r = 0.208, P < 0.001, respectively), and kidney volume/body length (r = 0.109, P = 0.010 and r = 0.194, P < 0.001, respectively) at 6 mo. Linear regression analyses showed a significant effect of free IGF-I on kidney volume in models, including significant effects of HP formula and anthropometry. The structural equation model revealed a significant direct effect of the HP formula on kidney volume and an indirect effect mediated by free IGF-I.
Conclusion: This study suggests that IGF-I partly mediates protein-induced kidney growth in healthy infants. IGF-I could be involved in a pathway for the programming of the renal system.
Trial registration: ClinicalTrials.gov NCT00338689.