Date

October 2009

Document Type

Thesis

Degree Name

M.S.

Institution

Oregon Health & Science University

Abstract

Background: Postprandial hyperlipidemia is associated with increased risk of cardiovascular disease (CVD). Low carbohydrate diets are a popular choice for weight-loss, but acute effects of low carbohydrate diets on postprandial plasma fatty acid concentrations have not been tested. Methodology: Ten healthy, normal weight adults participated in a randomized crossover feeding study. Subjects consumed a standard diet (51% carbohydrate, 14% protein, 35% fat) for 3 days. On day 4 participants consumed either low carbohydrate (4%) or high carbohydrate (58%) meals. Subjects then repeated the standard diet and alternate test meals after a minimum 3 day washout period. Blood samples were drawn at fasting (0800) and postprandially every hour for 9 ½ hours. Pre- and postprandial concentrations of plasma triacylglycerols, total non-esterified fatty acids and individual fatty acids were analyzed by modified Wahlefeld method, colormetric enzymatic assay, and gas chromatography/mass spectrometry, respectively. Differences between diets were compared by paired t-tests and contrast analyses. Results: Triacylglycerol (TAG) concentrations were significantly higher after the low carbohydrate meals compared to the high carbohydrate meals (Area under the curve [AUC] for TAG: low carbohydrate 1097 ± 108 and high carbohydrate 843 ± 89 mg∙h/dL, p <0.001). Saturated fatty acid concentrations were significantly higher throughout the sampling period after the low carbohydrate meals compared to the high carbohydrate meals (AUC low carbohydrate 35882 ± 2588 vs. high carbohydrate 27748 ± 2475 μmol/L, p = 0.002). AUC of monounsaturated fatty acid concentrations was higher after the low carbohydrate meals compared to the high carbohydrate meals (8462 ± 1077 vs. 6867 ± 647 μmol∙h/L, respectively, p = 0.049). There was no difference in AUC of total polyunsaturated fatty acids, or n-6 or n-3 polyunsaturated fatty acid concentrations between diets. Insulin concentrations were lower and non-esterified fatty acids concentrations were higher following the low carbohydrate meals compared to the high carbohydrate meals, (total insulin AUC 84 ± 9.9 vs. 240 ± 23 μIU∙h/ml, respectively, p < 0.01); total non-esterified fatty (AUC 3.46 ± 0.259 vs. 1.850 ± 0.257 mM·h, respectively, p = 0.002). Insulin was negatively correlated to non-esterified fatty acid concentrations following the high carbohydrate meals but not the low carbohydrate meals (p=0.002). Conclusions Plasma triacylglycerols, saturated fatty acids, monounsaturated fatty acids, and non-esterified fatty acid concentrations were higher and insulin concentrations were lower after the low carbohydrate meals compared to the high carbohydrate meals. Chronic elevation of postprandial lipids may contribute to the development of CVD. Funding Disclosure: This sub-study of the Energy Balance Study was funded by the OHSU Graduate Programs in Human Nutrition and grants from the NIH: National Center for Complementary and Alternative Medicine (1 R21 AT002753-01) and the National Center for Research Resources (1U L1RR024140).

Identifier

doi:10.6083/M4RR1W7H

Division

Graduate Programs in Human Nutrition

School

School of Medicine

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