Absorption Rates of Fructose and Influence of Fructose on the Glucose Blood Level in Preterm and Term Newborns Appropriate for Gestational Age as Compared to Preterm and Term Newborns Small for Gestational Age

Oral tolerance tests were performed with 2.0 and 3.0 g·kg^––1 fructose and the fructose and glucose blood levels were observed in preterm and term newborns appropriate for gestational age (AGA) and small for gestational age (SGA). Their age ranged from 12 to 72 h and from 10 to 12 days. The absorption rates of fructose – as compared with intravenous fructose infusions – in the groups examined amounted to 23–30%, but in preterm SGA newborns they reach a value of 67%. The elimination of fructose in the urine was less than 4% of the intake. Whereas preterm and term AGA newborns showed a clear increase of the glucose level irrespective of postnatal age, the glucose concentration was not influenced in preterm SGA newborns. Also in preterm SGA newborns the glucose blood level was increased by galactose during the first days of life, so that lack of increase of glucose after fructose in this group may possibly be due to a reduced gluconeogenesis at the level of hexose-1,6-diphosphatase.