Objectives and methods: Our goal was to describe nutritional homeostasis in healthy exclusively breastfed infants (n = 175) during their first 5 d, by cross-sectional measurements of body weight, blood glucose, plasma insulin, insulin-like growth factor-I (IGF-I), insulin-like growth factor binding-protein-1 (IGFBP-1), free fatty acids (FFA), glycerol, ketone (3-OH-butyric acid) and lactate. We also investigated whether nutrition affected feeding behaviour by timing the interval between feedings.
Results: A progressive loss of body weight, as percentage of birthweight, occurred up to 2 d of age, with a maximal decrease of 5.8 +/- 2.1% (mean +/- SD); this was accompanied by inhibition of anabolic hormone and metabolic pathways and an increased mobilization of stored fat and ketogenesis. The interval between feedings decreased between d 1 and 2. Weight gain occurred at 3 d and the following re-feeding phase returned fuel stores to their previous levels and established an anabolic hormonal and metabolic situation. Infants with weight loss exceeding 10% had a further accentuation in their peripheral picture of starvation and a further 7% shortening of the interval between feedings.
Conclusions: breastfeeding on demand is accompanied by a balanced nutritional situation and an increased drive to eat when weight reduction is <6%. However, a weight loss of > or = 10%, probably elicits hunger sensations in response to decreased fuel availability.