Effect of a low-fat diet on fatty acid composition in red cells, plasma phospholipids, and cholesterol esters : investigation of a biomarker of total fat intake

<b>Background</b>: The utility of fatty acids (FAs) as biomarkers of total fat intake is unknown.<br /><br /><b>Objective</b>: We compared FA changes in red cells (RCs), plasma phospholipids (PLs), and cholesterol esters (CEs) in response to a low-fat diet (LFD) and a moderate-fat diet (MFD) and assessed whether individual or combination of FAs predict LFD.<br /><br /><b>Design</b>: Postmenopausal women (<i>n</i> = 66) were randomly assigned to receive an LFD (17% of energy from fat) or an MFD (34% of energy from fat) for 6 wk. All foods were provided. FAs in diets and blood were determined by gas-liquid chromatography. FA changes between baseline and end of study were compared across diets by using <i>t </i>tests. FA predictors of an LFD were selected by logistic regression.<br /><br /><b>Results</b>: Many FAs in RCs, PLs, and CEs responded differently to the 2 diets. Changes from baseline with an LFD for palmitic acid (16:0) (3–11% increase), behenic (22:0) and lignoceric (24:0) acids (3–20% decrease, in RCs and PLs only), <i>cis</i>-monounsaturated FA (MUFA) (25–35% increase), linoleic acid (18:2n–6) (11–13% decrease), trans octadecanoic acids (trans 18:1) (7–20% decrease), and n–6 highly unsaturated FA (HUFA) (2–8% increase) were significantly different from changes with an MFD. Individually, 18:2n–6 and <i>trans</i> 18:1 were strong predictors of an LFD [receiver operating characteristic (ROC) curves: 0.92–0.80). A logistic regression model with <i>trans</i> 18:1, 18:2n–6, and vaccenic acid (18:1n–7) predicted an LFD with high specificity and sensitivity (ROC curves: 0.99).<br /><br /><b>Conclusions</b>: Saturated FA, cisMUFA, n–6 HUFA, and exogenous FAs greatly differed in their response to the LFD and MFD. Parallel responses were observed in RCs, PLs, and CEs. A model with a combination of FAs almost perfectly differentiated the consumption of 34% fat from that of 17% fat.<br />