The influence of nutrition on IGF-1 in tube-fed profoundly retarded adults

This study was conducted to determine whether IGF-I concentrations are low in nonambulant profoundly retarded adults and to identify associated nutritional factors.

Serum IGF-I, albumin, pre-albumin, creatinine, zinc (Zn) and plasma amino acids were measured before and after a four-week 25% increase in formula in 25 individuals, divided into those fed by day (Group A) or by night (Group B).

Circulating IGF-I was low in nine of the 22 subjects (40.9%) included in the analysis. Mean IGF-I increased 10.4% (p=0.004). Despite high intakes of essential amino acids and Zn, initial mean plasma tryptophan and phenylalanine were low, and serum Zn was low in 40.9% of subjects. Plasma tryptophan was low at both samplings and correlated with circulating IGF-I concentrations (p=0.02) at the beginning of the study. Serum IGF-I and Zn also correlated (p=0.02) initially.

IGF-I is commonly low in this population and is associated with low plasma amino acid and Zn concentrations, despite high intakes of these nutrients. The causes and clinical implications of these abnormalities need further study.