Trans fatty acids (TFAs), especially elaidic acid, formed during partial hydrogenation of vegetable oils have been shown to increase LDL-cholesterol (LDL-C) and decrease HDL-cholesterol (HDL-C), thereby increasing the LDL-C/HDL-C ratio and elevating the risk of cardiovascular disease. However, studies on the health effects of ruminant TFAs have suggested that these TFAs, which are primarily vaccenic acids, have no or inverse association with coronary heart disease. Thus, dietary recommendations or legislation for TFAs should consider the differences in the physiological effects of TFAs derived from various food sources. This present review recapitulates the progress in TFA research by analyzing recent epidemiological studies or intervention studies and comparing the cardiovascular health effects of industrially produced TFA and ruminant TFA.