OBJECTIVE: High infancy levels of insulin-like growth factor-I (IGF-I) have been associated with increased linear growth and fat-free mass (FFM) but also with risk of obesity. This paper examines how IGF-I at 9 and 36months relates to diet and body composition.

DESIGN: Healthy term infants from the prospective cohort study, SKOT, were examined at 9 and 36months with anthropometry, bioelectrical impedance (36months), 7-day food records and blood analysis of IGF-I and IGFBP-3 by chemiluminescent immunometric assay.

RESULTS: IGF-I at 36months (n=229) was positively correlated with 9months values and values were considerably higher in girls (43%). Children breastfed at 9months had lower IGF-I concentrations at 9months but reached the same IGF-I concentrations at 36months as infants not breastfed at 9months. IGF-I at 36months was positively associated with height, weight, BMI, predicted FFM and FFM index (FFM/height (kg/m(2))). Although there also was a positive association with predicted fat mass (FM) there was no association with FM index (FM/height (kg/m(2))). Further, a negative association with skin fold thickness was observed. A change in IGF-I from 9-36months was positively related to FFM and FFM index but not BMI, FM and FM index. No associations were seen between IGF-I and current intake of milk, meat or protein energy percentage, but both fat and saturated fat energy percentage were negatively associated with IGF-I.

CONCLUSION: IGF-I concentrations were positively associated with growth but not with adiposity at this age. However, the higher tempo of growth may influence age at adiposity rebound and thereby later risk of obesity. Milk and protein intake at 36months did not influence IGF-I but there was a negative association with intake of fat and saturated fat. The implications of this finding for development of obesity need further exploration.