Abstract
Background/Objectives: Circulating amino acid concentrations and their excretion can provide insights into dietary protein intake and metabolism. Alterations in amino acid homeostasis occur in various disorders due to nutritional imbalances or metabolic changes, including obesity. A ketogenic diet (KD) has gained popularity for weight management; however, its metabolic effects are not fully known. Therefore, the aim of this study was to evaluate the effect of an eight-week, energy-restricted Mediterranean-type KD on the amino acid metabolism in women with overweight and class I obesity. Methods: A randomized, single-center, controlled trial was conducted with 80 women with a BMI of 25.5-35 in age between 18 and 45 years, without any chronic diseases. Randomly divided women received food catering with approximately 1750 kcal daily for eight weeks, containing KD or standard diet (STD), respectively. The concentration of amino acids was assessed by gas chromatography-mass spectrometry after the derivatization with chloroformate in serum and urine collected at the baseline, after 4 weeks, and at the end of the intervention. Results: The results collected from 66 participants were included in the final analyses. Independent of diet type, weight reduction was associated with increased circulating α-aminobutyric acid and decreased proline, glutamate, and tyrosine. The KD led to lower concentrations of alanine, methionine, threonine, and tryptophan, alongside higher levels of branched-chain amino acids (BCAA) and α-aminobutyric acid compared to the STD. Urinary amino acid excretion decreased after weight reduction. KD was associated with higher urinary excretion of BCAA and β-aminoisobutyric acid. Conclusions: In summary, both weight reduction and KD significantly affect the amino acid metabolism, which might have implications for inflammation, oxidative stress, and cardiometabolic risk.