This study shows that TFAs from industrially produced and from natural sources have different effects on CVD risk factors in women. The HDL cholesterol-lowering property of TFAs seems to be specific to industrial sources. However, it is difficult in the present study to draw a conclusion about the effect of TFAs from either source on absolute CVD risk in these normolipidemic subjects. The mechanism underlying the observed sex- and isomer-specific effects warrants further investigation.