Some LDL-Cholesterol Particles Are Worse Than Others

Consuming higher levels of dietary trans fatty acids is associated with higher blood levels of small, unhealthy particles of low-density lipoproteins (LDL), according to a recent study funded in part by the Agricultural Research Service. ARS is the U.S. Department of Agriculture's chief scientific research agency.

When lipoprotein particles are formed within cells, phospholipids and apoproteins make up the surface, while triglyceride and cholesterol form the core.

LDLs circulate in the bloodstream as populations of small, medium or large particles, which carry the majority of cholesterol to parts of the body and are therefore referred to as "bad" cholesterol. Smaller particles accumulate within blood more readily than larger particles. Unfortunately, previous research has shown that even among people with normal blood levels of LDL-cholesterol, those with high levels of smaller-sized LDL particles are at significantly increased risk of heart disease.

In the study, 36 volunteers were provided with five 35-day experimental diets. Key test ingredients with varying levels of trans fatty acids were semiliquid margarine (very low), soft margarine (mildly low), shortening (intermediate), stick margarine (high), or butter (low in trans fatty acids, high in saturated fat). The researchers found an increase in small and more compact LDL-cholesterol particles with increased consumption of trans fatty acids.

Trans fatty acids are formed during the manufacturing process called hydrogenation, in which oil is transformed from a liquid to a more versatile, solid fat. These hydrogenated oils are used in thousands of processed foods, such as commercially baked goods and margarines.

The ARS-funded scientists who, with several colleagues, conducted the study are Alice H. Lichtenstein and Susan M. Jalbert, with the Cardiovascular Nutrition Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, Mass.

The scientists concluded that the results reinforce the importance of consuming diets low in trans fatty acids to improve lipoprotein profiles. Manufacturers will be required to list the content of trans fatty acids on food labels by January 1, 2006.