Trans fatty acids raise plasma low-density lipoprotein (LDL) cholesterol levels in volunteers when exchanged for cis unsaturated fatty acids in the diet. In addition, trans fatty acids may lower high-density lipoprotein (HDL) cholesterol levels and raise triglyceride and lipoprotein(a) levels in plasma. Trans and cis unsaturated fatty acids are thus not equivalent, and diets aimed at reducing the risk of coronary heart disease should be low in both trans and saturated fatty acids.