Elevated Plasma Tryptophan in Patients with Anorexia Nervosa Compared with Hypotrophic Controls

Introduction: We hypothesized that anorexia nervosa (AN) is associated with pathological amino acid metabolism. This study aimed to identify amino acids exhibiting abnormal metabolism in patients with AN compared with those in low Methods: This was a single-center, retrospective, observational study that compared patients with AN with a low-nutrient control group. All participants were admitted to the Kitasato University Hospital Emergency Center between January 1, 2018, and January 31, 2021. Both the AN and low-nutrient control groups had five patients each. Plasma amino acid category testing was conducted at the same institution for both groups. Patient sex, age, height, weight, and comorbidities were retrospectively extracted. Plasma amino acid fractions, total amino acids, total essential amino acids, total nonessential amino acids, branched-chain amino acids (sum of valine, isoleucine, and leucine), and amino acid concentrations and ratios were compared between the two groups. Data were analyzed using the Mann-Whitney U test. Results: Body mass index was lower in the AN group (p = 0.00794). Tryptophan levels were significantly higher in the AN group (p = 0.00794). Other amino acid values, the sum of amino acid values, and amino acid ratios were not significantly different between both groups. Conclusions: Serum tryptophan levels were higher in the AN group than in the low-nutrient group, and AN may be associated with abnormal amino acid metabolism.