Trans fatty acids and LDL particle size - Lipids - low density lipoproteins

Nutrition Research Newsletter,  Oct, 2003  

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Trans fatty acids are unsaturated fatty acids containing greater than one double bond in trans configuration. It is well known that the consumption of dietary trans fatty acids increases plasma LDL-cholesterol concentrations and elevated plasma LDL cholesterol is one of the most important risk factors for the development of cardiovascular disease. This effect was shown to be proportional to dietary trans fatty acid intake and is not related to changes in endogenous cholesterol synthesis.

Environmental factors such as the fatty acid content of the diet may affect the diameter and density of LDL particles to a significant extent. Diets enriched with saturated fatty acids are associated with large and cholesterol-rich LDL particles whereas diets that are low in fat are associated with reduced LDL particle size. Although the effect of dietary trans fatty acids on plasma LDL cholesterol levels is well known, there is no current documentation on how dietary trans fatty acids modulate LDL particle size and cholesterol distribution among different LDL subclasses. Therefore, some Canadian researchers investigated the effect, relative to that of butter and commercially available hydrogenated vegetable fats having a wide range of trans fatty acid concentrations on LDL particles size and distribution in moderately hypercholesterolemic men and women.

Eighteen men and 18 women each consumed five experimental diets in random order for 35-day periods. All diets were designed to provide 15% of energy from protein, 55% from carbohydrate and 30% from fat. The only difference between the diets was the form in which two-thirds of the fat was provide (i.e. as soybean-oil based margarines hydrogenated to various extents or as butter). LDL particle size and distribution were characterized by non-denaturing, 2% to 16% poly-acrylamide gradient gel electrophoresis. A lipid profile was measured after the subjects gave fasting blood samples.

Serum total and LDL-cholesterol levels increased progressively with the degree of enrichment of the diet with trans fatty acids (from semi-liquid to stick margarine). However, total and LDL-C reached the highest concentrations after the subjects consumed the butter-enriched diet. Increased consumption of trans fatty acids was also related to a more subtle but significant increase in serum triacylglycerol concentration. Relative to the LDL particle size observed after consumption of the butter-enriched diet, LDL particle size decreased significantly and in a dose-dependent fashion with increasing amounts of dietary trans fatty acids. Cholesterol levels in large and medium-sized LDL particles also increased proportionately to the amount of trans fatty acids in the diet.

In conclusion, the consumption of trans fatty acids has a negative effect on LDL particle size, thus further contributing to the overall effect of trans fatty acids on cardiovascular disease. The data also indicate that the increase in plasma LDL-cholesterol concentration associated with increased dietary trans fatty acid content cannot be due to a specific LDL subspecies, but is instead related to the distribution of particle size. The result reinforce the importance of promoting diets that are low in saturated fat and those that contain a minimal quantity of trans fatty acids from hydrogenated fat, in order to favorably affect the lipoprotein profile, and thus contribute to a reduced risk of cardiovascular disease.

Jean-Francois Mauger, Alice Lichtenstein, Lynne Ausman, et al., Effect of Different Forms of Dietary Hydrogenated Fats on LDL Particle Size, Am J Clin Nutr 78: 370-375 (September 2003). [Address reprint requests to B Lamarche, Institute on Nutraceuticals and Functional Foods, Pavillon Paul Comtois, local 2423, Universite Laval, Quebec, Canada G1K 7P4. E-mail: benoit.lamarche@inaf.ulaval.ca]

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