New multipliers for estimating the phenylalanine content of foods from the protein content

Abstract

Phenylalanine (Phe) is a key nutrient in the dietary management of phenylketonuria (PKU). Since the protein content of many foods is readily available, estimating the Phe content of a food is facilitated by an understanding of the statistical distribution of the Phe:protein ratio in common foods. In particular, from the minimum and maximum Phe:protein ratio, one can obtain an upper bound and a lower bound on the Phe content of any given food from its protein content. Currently, the multipliers commonly used are 30 and 50. In this document, we present and compare the statistical distribution of the Phe:protein ratio in two databases, namely the USDA National Nutrient Database and the Danish Food Composition Databank. Based on this data, we suggest replacing the 30–50 multipliers by 20–65. When used to estimate the Phe content from the protein content, these multipliers yield estimates that are correct for more than 97% of the data analyzed (as opposed to less than 76.3% for the multipliers 30–50). Furthermore, we confirm that the commonly used average of Phe:protein ratio for the foods in the categories of fruits (30) and vegetables (40) are more or less accurate.