Introduction: Celiac disease (CD) is associated with an increased risk of major depressive disorder, possibly due to deficiencies in micronutrients in the gluten-free diet. We aimed to investigate whether essential amino acids (i.e., the precursors of serotonin, dopamine and other neurotransmitters) are depleted in the diet and serum of CD patients with major depressive disorder.

Methods: In a cross-sectional study we assessed dietary intake of amino acids and serum levels of amino acids, including in 77 CD patients on a gluten-free diet and in 33 healthy controls. , major depressive disorder was assessed with structured interviews (using the Mini International Neuropsychiatric Interview Plus). Dietary intake of amino acids was assessed (using a 203-item food frequency questionnaire), and serum levels of amino acids were assessed.

Results: Participants had a mean age of 55 years and 74% were women. The intake of vegetable protein was significantly lower in CD patients than in healthy controls (mean difference of 7.8 g/d; 95% CI: 4.7 - 10.8), as were serum concentrations of tyrosine, phenylalanine and tryptophan (all p < 0.005). However, within the CD patient groups, the presence of major depressive disorder (n = 42) was not associated with intake or serum levels of essential amino acids.

Conclusions: We found that patients with CD on a long-term successful gluten-free diet, with good adherence, consume significantly less vegetable protein than controls, and their serum levels of several essential amino acids were also lower in CD versus controls. Despite its potential adverse effect, intake and serum levels of essential amino acids were not related to major depression.