Lysine from Whole Wheat Bread Consumed by Healthy Adult Males Has High Metabolic Availability When Assessed Using the Indicator Amino Acid Oxidation Method.

ABSTRACT

BACKGROUND: The protein quality of wheat is limited by its low content of the indispensable amino acid (AA) lysine and the metabolic availability (MA) of lysine in wheat bread for humans is unknown. OBJECTIVES: The study objective was to determine the MA of lysine in whole wheat bread. METHODS: Five healthy young males (≤30 y, body mass index <25) were studied in a repeated-measures design using the indicator amino acid oxidation (IAAO) method, with L-[1-13C] phenylalanine as the indicator. Each received 7 levels of lysine intakes in random order; 4 levels of L-lysine; 5, 8, 12, and 15 mg/kg/d (reference diet), and 3 intakes of lysine from whole wheat bread (test diet). The MA of lysine in whole wheat bread was assessed by comparing the IAAO response to the test diet (whole wheat bread) with the IAAO response to the reference diet using the slope ratio method. RESULTS: The MA of lysine from whole wheat bread was 90%. CONCLUSIONS: Lysine has a high MA but it is still limiting in whole wheat bread due to its low concentration. A combination of wheat with a complementary protein source (that is, lentils which are sufficient in lysine) is recommended to meet the lysine requirement in a wheat-based diet for healthy young males. This trial was registered at clinicaltrials.gov as NCT03674736 and NCT03200652.