A novel method for the biological evaluation of protein quality using plasma somatomedin-C (insulin-like growth factor-1) measurement.

The objective of the present study was to investigate the validity of plasma somatomedin-C insulin-like Growth Factor-1 (IGF-1) measurement for the evaluation of protein quality. Six sources of protein were evaluated using the conventional methods: protein efficiency ratio (PER), net protein ratio (NPR), relative protein value (RPV), biological value (BV) and protein digestion coefficient (D). Plasma IGF-1 level was also measured on the third day of the feeding period. Plasma levels of IGF-1 ranked the protein sources in the same order as other conventional methods. In addition, values of IGF-1 correlated significantly with the values of PER, NPR, RPV and BV. Protein digestion values correlated poorly with the other methods being used. We conclude that the measurement of plasma IGF-1 is a valid, reliable, easy and rapid method for protein quality evaluation to be used by the food industry and compliance regulatory agencies. Furthermore, this method could be employed for the evaluation of protein quality in infant formulas and for pre-clinical evaluation of enteral formulas.