Abstract
BackgroundDietary intervention trials rely on self-reported measures of intake for assessment of energy and macronutrient composition. Dietary fat intake is of particular interest due to strong associations with pathophysiology. In epidemiological trials phospholipid fatty acid composition may reflect composition of habitual diet, although strong correlations have been identified only for essential polyunsaturated fatty acids (PUFAs). Preliminary evidence shows that saturated fatty acids (SFA) C15:0 and C17:0 may be acceptable biomarkers. This study measured changes in erythrocyte membrane fatty acids during a period of strictly controlled fat feeding to investigate their use as a short-term marker of compliance, particularly for intake of SFAs.ResultsThis was a randomised cross-over trial in which diet was provided and strictly controlled. 20 healthy, male subjects were given a 40 energy % (en%) fat diet, high in saturated (high-SFA, 20 en%) or unsaturated (high-USFA, 24 en%) fatty acids for 2 periods of 3 weeks. Subjects were residential during intervention with all food and beverages provided. Dietary composition was verified by direct chemical analysis. Blood samples were collected on days 1,7,14, 21 and analysed for red blood cell (RBC) membrane fatty acid composition. Pearson correlation showed RBC fatty acid composition to mimic dietary composition by 3 weeks, but the relationships were weak. Of the SFAs only RBC C16:0 decreased in response to decreased dietary content on high-USFA treatment (ANOVA, diet, P < 0.05). Of the USFAs, higher levels of C18:1 MUFA, C20:4 and C22:6 long chain PUFA on high-USFA diet lead to higher C18:1, C20:4 and C22:6 within RBCs (ANOVA, time*diet, P < 0.05). Pearson's correlation was significant between dietary and RBC fatty acids during the 21d dietary manipulation for C18:1, and C20:5, C22:6 only (P < 0.05).ConclusionRBC membrane fatty acids cannot reliably be used as an independent measure of compliance for dietary SFA intake in short-term studies. The MUFA oleic acid and PUFAs EPA and DHA may be more useful as markers of compliance during short term intervention trials.
Highlights
Dietary intervention trials rely on self-reported measures of intake for assessment of energy and macronutrient composition
saturated fatty acids (SFA), saturated fatty acid; monounsaturated fats (MUFA), monounsaturated fatty acid; polyunsaturated fatty acids (PUFAs), polyunsaturated fatty acid. % peak area calculated from fatty acid methyl esters (FAMEs)
The high-SFA and high-USFA dairy lipids used in the two diets resulted in a significant difference between dietary treatments for all fatty acids measured other than C16:1 trans and the n-3 PUFA
Summary
Dietary intervention trials rely on self-reported measures of intake for assessment of energy and macronutrient composition. This study measured changes in erythrocyte membrane fatty acids during a period of strictly controlled fat feeding to investigate their use as a short-term marker of compliance, for intake of SFAs. Assessment of dietary intake through food records or even weighed food intake is commonly subject to bias, provides only a poor estimate of current and/or habitual diet, and leads to widespread misreporting of energy and nutrient intake [1,2,3,4,5,6,7]. We were interested in evaluating the use of biomarkers to assess the 3 major classes of fatty acids in subjects whose dietary intake was both fixed and known through provision of all dietary fats during a residential nutrition trial, with a particular interest in determining possible biomarkers of dietary SFA. A MUFA-enriched diet has been shown to increase circulating MUFA content in several trials [12,15,27], but this finding is not universal
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