Trans monounsaturated fatty acids (TFA) are hypercholesterolemic compared to oleic acid to a degree approaching or equivalent to saturated FA. However, it is unknown to what extent these effects may be due to cholesterol lowering by oleic acid rather than elevation by saturated FA and TFA. In order to better understand the impact of replacing TFA in foods, it is first necessary to know the relative lipid-modifying effects of the major FA that change as TFA are lowered or removed. For 5 wk, 50 normocholesterolemic men were fed controlled diets providing approximately 15% of energy from protein, 39% from fat, and 46% from carbohydrate in a randomized, 6×6, crossover design. Eight percent of energy was replaced across diets with the following: carbohydrate (CHO) (1∶1 simple to complex); oleic acid (OL); TFA; stearic acid (STE); TFA/STE (4% of energy from each); carbon 12∶0 16∶0 saturated FA (LMP). LDL cholesterol concentrations (mmol/l) were as follows (different superscripts indicate significance at P≤0.01): OL 2.95a; CHO 3.05a,b; STE 3.10b,c; LMP 3.21c,d; TFA+STE 3.32d,e; and TFA 3.36e. HDL cholesterol concentrations (mmol/L) were as allows: STE 1.16a; IFA 1.16a,b; TFA/STE 1.17a,b; CHO 1.19b; OL 1.24c; and LMP 1.30d. Triacylglycerides were highest after STE (1.13) and lowest after OL (0.88) (P<0.001). Thus, compared to the carbohydrate control diet, TFA raised LDL cholesterol at least equivalent to LMP but had no effect on HDI cholesterol; STE had no effect on LDL cholesterol but lowered HDL cholesterol; LMP raised both LDL cholesterol and HDL cholesterol; and oleic acid raised HDL cholesterol but had no effect on LDL cholesterol.
This work was supported by the IAFNS Lipids Committee. See all of our work on trans fatty acids.