This project studies associations between circulating odd-chain fatty acids and dairy and fiber intake among post-MI Dutch patients. Circulating odd-chain fatty acids pentadecanoic (15:0) and heptadecanoic acid (17:0) are considered to reflect dairy intake. In cohort studies, higher circulating 15:0 and 17:0 were associated with lower type 2 diabetes risk. A recent randomized controlled trial in humans suggested that fiber intake also increased circulating 15:0 and 17:0, potentially resulting from fermentation by gut microbes. We performed cross-sectional analyses in a subsample of 869 Dutch post-MI patients of the Alpha Omega Cohort who had data on dietary intake and circulating fatty acids. Dietary intakes (g/d) were assessed using a 203-item food frequency questionnaire. Circulating 15:0 and 17:0 (as % of total fatty acids) were measured in plasma phospholipids (PL) and cholesteryl esters (CE). Spearman correlations (rs) were computed between intakes of total dairy, dairy fat, fiber, and circulating 15:0 and 17:0. Patients were on average 69 years old, 78% was male and 21% had diabetes. Total dairy intake comprised predominantly milk and yogurt (69%). Dairy fat was mainly derived from cheese (47%) and milk (15%), and fiber was mainly from grains (43%). Circulating 15:0 in PL was significantly correlated with total dairy and dairy fat intake (both rs=0.19, p<0.001), but not with dietary fiber intake (rs=0.05, p=0.11). Circulating 17:0 in PL was correlated both with dairy intake (rs=0.14 for total dairy and 0.11 for dairy fat, p<0.001), and fiber intake (rs=0.19, p<0.001). Results in CE were roughly similar, except for a weaker correlation of CE 17:0 with fiber (rs=0.11, p=0.001). Circulating 15:0 was highest in those with high dairy intake irrespective of fiber intake, while circulating 17:0 was highest in those with high dairy and fiber intake. To conclude, in our cohort of post-MI patients, circulating 15:0 reflected dairy intake but not fiber intake, whereas circulating 17:0 reflected both dairy and fiber intake. These data suggest that cardiometabolic health benefits previously attributed to 17:0 as a biomarker of dairy intake may partly be explained by fiber intake.