16 Chapter 1 intake needs to be combined with sufficient fatty acids and carbohydrates, resulting in a high energy diet of 95-140 kcal per kg per day. In an attempt to prevent complications from the high energy and high protein diet, nutritional intake has to be build up in the first week of life causing relative malnutrition in this period. Moreover, parenteral nutrition is required until the preterm infant is able to tolerate full enteral feeds and studies have shown that parenteral nutrition, in contrast to enteral feeding, is associated with lower IGF-I levels. (21, 22) In addition, the type of enteral nutrition, i.e. own mother’s milk, donor human milk or formula, influences IGF-I levels. (23) Furthermore, macronutrient intake has been linked to body composition. A high protein intake has been associated with decreased fat mass and increased fat free mass in infancy. (24, 25) Therefore, the route of administration and the type of nutrition play a vital role in optimizing postnatal growth and body composition. Aims and objectives The research outlined in this thesis aims to explore the postnatal modulation of growth and body composition in very preterm and extremely preterm infants (gestational age at birth 24 – 32 weeks). Furthermore, the influence of the developing endocrine axis on health outcomes in infancy is investigated. It is hypothesized that: • IGF-I has to reach a threshold concentration before it can effectively influence growth. Once IGF-I passes this threshold concentration, themaximumgrowth rate is expected to be potentiated by IGF-I; • In states with low IGF I levels to ensure an easily accessible energy store, but resulting in an increased fat mass percentage at term age; • Before IGF-I reaches the threshold con, such as critical illness, nutrient restriction and extreme prematurity, the IGF system would stimulate mesenchymal stemcell differentiation towards adipogenesis as amechanism centration, a high-energy and high-nutrient diet is required to potentiate growth; • Once IGF-I reaches the threshold concentration, a continued high-energy and high-nutrient diet could potentially lead to increased fat deposition; • The protective effect on inflammation and the anti-oxidative effects of IGF-I may be important in decreasing the risk of developing comorbidities. To investigate these hypotheses a longitudinal cohort study was designed and literature reviews were conducted. In this thesis all papers, except the literature reviews, are based on the results of the Nutrition in relation to the endocrine regulation of preterm growth study (NUTRIE study).
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