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BACKGROUND: Objective biomarkers of diet, such as metabolomics, may improve dietary assessment and provide additional insight into how diet influences disease risk. The portfolio diet, a cholesterol-lowering plant-based diet, is recommended for lowering low-density lipoprotein cholesterol (LDL-C). This diet is low in saturated fat and includes nuts, plant protein (legumes), viscous fiber, and phytosterols.OBJECTIVE: We examined metabolomic profiles in response to the portfolio diet in two randomized controlled trials (RCTs), where all foods were provided to the participants, compared to a control vegetarian diet and the same control diet with a statin.METHODS: The first RCT included 34 adults (age 58.4 ± 8.6 y) and the second RCT included 25 adults (age 61.0 ± 9.6 y), all with high LDL-C (>4.1 mmol/L). Plasma samples were obtained at baseline, week 2, and week 4 in both RCTs for metabolomics analysis using liquid chromatography-tandem mass spectrometry. Linear mixed models were used to examine effects of the interventions on the metabolites in each RCT, applying a Bonferroni correction.RESULTS: Of 496 known metabolites, 145 and 63 metabolites significantly changed within the portfolio diet interventions in the first and second RCT, respectively. The majority were glycerophosphocholines (32%), triacylglycerols (20%), glycerophosphoethanolamines (14%), sphingomyelins (8%), and amino acids and peptides (8%) in the first RCT, and glycerophosphocholines (48%), glycerophosphoethanolamines (17%), and amino acids and peptides (8%) in the second RCT. Fifty-two metabolites were consistently changed in the same direction with the portfolio diet intervention across both RCTs, after Bonferroni correction.CONCLUSIONS: Many of these metabolites likely reflect the plant-based nature, low saturated fat content, and cholesterol-lowering effects of the diet, such as increased N2-acetylornithine, L-pipecolic acid, lenticin, and decreased C18:0 lipids and cholesteryl esters. Further research is needed to validate these metabolites as biomarkers of a plant-based dietary pattern.