The IGF-system is not affected by a twofold change in protein intake in patients with type 1 diabetes

Abstract

Objective In type 1 diabetes the circulating IGF-system is altered with low IGF-I and changes in levels of IGF-binding proteins (IGFBPs) which may be of importance for the development of diabetes complications. Our aim was to study if IGF-I, as supported by experimental data in animals, can be affected by dietary protein intake. Design and methods Twelve patients with type 1 diabetes, age 37.5 ± 10.0 years (mean ± SD), diabetes duration 20.1 ± 9.3 years and HbA1c 6.3 ± 0.6% were allocated to isocaloric diets with either low normal protein content (LNP), (10 E%; 0.9 g protein/kg body weight) or high normal protein content (HNP) (20 E%; 1.8 g protein/kg body weight) in an open randomised cross-over study. Each diet was taken for 10 days with a wash-out period of 11 days in between. Circulating levels of total and free IGF-I and -II, IGFBP-1, -2 and -3 and GH-binding protein (GHBP) as well as ghrelin were measured with validated in-house immunoassays. Results At day 10, urinary urea excretion was 320 ± 75 mmol/24 h during LNP diet compared with 654 ± 159 mmol/24 h during HNP diet ( p < 0.001). There were no changes in body weight or glycaemic control between the diets. Fasting levels of total IGF-I were 121 ± 33 μg/L after LNP and 117 ± 28 μg/L after HNP diet (ns) and the corresponding concentrations of IGFBP-1 were 142(141) and 132(157) μg/L [median (IQR)] (ns). There were no differences in plasma concentrations of total IGF-II, free IGF-I and -II, IGFBP-3, GHBP and ghrelin, whereas a small difference was found for IGFBP-2 (302 ± 97 vs. 263 ± 66 μg/L; LNP vs. HNP; p < 0.04). Conclusions A twofold change of the dietary protein intake does not influence the altered circulating IGF-system in type 1 diabetes. In order to affect the IGF-system other interventions must be used.