Available Lysine in Foods as Determined in Adult Ileostomates

When foods are subjected to heat and pressure, a proportion of lysine is structurally altered and some will revert to lysine because of acid hydrolysis during amino acid analysis. Altered lysine molecules may be partly absorbed but are not utilized post-absorption.

A guanidination-based bioassay has been developed to determine true ileal digestible reactive lysine but it was only used in animal models (pig and rat). The objective of this study was to apply the assay and determine whether there is a difference between true ileal digestible total lysine and true ileal digestible reactive lysine in adult human ileostomates.

Six cooked or processed foods were analyzed for total lysine and reactive lysine. Six adults with a fully functioning ileostomy (4 women and 2 men; age range: 41-70 y; BMI: 20.8-28.1) participated. Foods for which total lysine > reactive lysine (cooked black beans, toasted wheat bread, and processed wheat bran), as well as a protein-free diet, were consumed by the ileostomates (n = 5 to 8; test food meals contained 25 g protein) and ileal digesta was collected. Each food was ingested twice by each participant, and the digesta was pooled. The order of foods for each participant was determined according to a Youden square. True ileal digestible total lysine and true ileal digestible reactive lysine were determined and a 2-way ANOVA model was used to analyze data.

True ileal digestible reactive lysine was significantly lower than true ileal digestible total lysine for cooked black beans, toasted wheat bread, and processed wheat bran by 89%, 55%, and 85%, respectively (P< 0.05).

True ileal digestible reactive lysine was lower than true ileal digestible total lysine, similar to that previously reported in pigs and rats, demonstrating the importance of determining the true ileal digestible reactive lysine contents of processed foods.