Circulating Levels of Branched-Chain Amino Acids Are Associated with Diet: A Cross-Sectional Analysis

<b>Background:</b> Higher circulating branched-chain amino acids (BCAAs) are linked to cardiometabolic and neurological diseases. While diet is the primary BCAA source, its impact on circulating levels remains unclear. This study examined the association between dietary intake and circulating BCAA concentrations in a large population-based sample. <b>Methods:</b> Data from 2159 participants (58.2% women, mean age 53.4 ± 8.6 years) were analyzed. Dietary intake was assessed using a questionnaire covering 91 individual food items, 9 nutrient categories, and 3 dietary patterns. BCAA concentrations were measured via LC-MS. All analyses were stratified by gender. <b>Results:</b> Circulating BCAA levels were higher in men than in women. BCAA levels were negatively associated with vegetables (standardized β = -0.029, <i>p</i> = 0.088; -0.051, <i>p</i> = 0.003; -0.038, <i>p</i> = 0.043 for leucine, isoleucine, and valine, respectively), dairy (-0.037, <i>p</i> = 0.029; -0.063, <i>p</i> < 0.001; -0.041, <i>p</i> = 0.028), and fruit (-0.031, <i>p</i> = 0.084; -0.039, <i>p</i> = 0.030; -0.041, <i>p</i> = 0.034), and a positive trend was observed for meat and meat-derived products, but the associations did not reach statistical significance. Vegetal protein, total carbohydrates, and monosaccharides showed a significant negative association with circulating BCAAs levels. Participants who complied with "dairy ≥ 3/day", "meat ≤ 5/week", or "at least three guidelines" had lower circulating BCAA levels. <b>Conclusions:</b> Circulating BCAA levels were negatively associated with dairy, vegetables, fruits, plant protein, carbohydrates, non-digestible fiber, calcium, and iron. While circulating BCAA levels were linked to meat consumption and adherence to dietary guidelines, the association was not linear. Differences were observed between men and women, which may be attributed to variations in dietary intake and preferences.