 Ruminant trans fatty acids rTFA will come from an experimental butter formulated from dairy fat obtained after having modified the regimen of lactating cows. All diets will be identical in terms of menus, calories and macronutrient composition with the exception of TFA levels. All foods will be provided to study participants. Based on a 2500 kcalday regimen, an intake of 4.1g of rTFA will represent 37 kcalday 1.5 of energy intake while the intake of 0.7 g of rTFA in the control diet will represent 6 calories 0.3 of energy. The 2 experimental diets will be formulated so that the percentage of daily calories from fat 33, carbohydrates 52 and proteins 15 will meet the dietary recommendations of the American Heart Association and the NCEP for primary prevention of CVD. 