A chemical score to evaluate the protein quality of commercial parenteral and enteral formulas: emphasis on formulas for patients with liver failure.

Essential amino acids, found in abundance in high-quality dietary protein, are required daily by hospitalized patients and healthy persons to maintain the dynamic process of protein metabolism. One method for assessing dietary protein quality is by determining a diet's chemical score, ie, the ratio of a gram of the limiting amino acid in a test diet to the same amount of the corresponding amino acid in a reference diet (eg, whole-egg protein) multiplied by 100. This investigation used the chemical score to evaluate the protein quality of 9 parenteral and 17 enteral diets commonly used to feed hospitalized patients. Standard parenteral and enteral products (ie, formulas that had not been designed for patients with a specific disease state) had chemical scores that ranged from 46% to 70%. Limiting amino acids were either methionine (plus cysteine) or phenylalanine (plus tyrosine). Products designed for patients with renal failure had the highest scores, which ranged from 85% to 145%. Products that were enriched with branched-chain amino acids for trauma patients had scores that ranged from 38% to 73%. The only product available for patients with pulmonary compromise had a score of 50%. The lowest scores, which ranged from 5% to 13%, were found in products for patients with hepatic failure. All products, except those with chemical scores below 13%, may be fed in relatively small amounts of protein (7 to 33 g) to satisfy the minimum daily requirements of essential amino acids, although such levels would not meet minimal daily nitrogen requirements. We recommend that dietitians use the chemical score to assess the protein quality of parenteral and enteral diets.