The World Health Organization (WHO) has recommended that trans fatty acid (TFA) intake should be less than 1% of total energy intake, but few data are available as to the influence of energy TFA intake of as low as 1% on blood cholesterol levels. A randomized, double-blind, parallel trial was conducted to assess the effects of 1% TFA dietary supplementation on serum cholesterol levels in healthy young women. Sixty-five volunteers consumed cookies containing 1% (TFA) or 0.04% (control) energy of TFA for 4 weeks and blood was harvested after overnight fasting. There were no significant differences in serum LDL- or HDL-cholesterol levels between the two groups. The hemoglobin A1c level was not influenced by dietary TFA. These results suggest that energy of TFAs at less than 1% has little effect on serum cholesterol or hemoglobin A1c levels in healthy young women. This confirms the correctness of the WHO recommendation.