Effect of trans fatty acid isomers from ruminant sources on risk factors of cardiovascular disease: study design and rationale.

Substantial evidence clearly demonstrates the deleterious effects of industrially-produced trans fatty acids (TFA); however, data are lacking from large, well controlled human feeding studies that directly compare the effects of industrially-produced and naturally-occurring TFA. The purpose of the current study is to determine whether consumption of TFA derived from different sources differentially affect risk factors of cardiovascular disease (CVD). The study was a randomized, crossover design, controlled-feeding intervention designed to compare the effects of the following diet treatments on risk factors of CVD: low TFA diet (base diet, 34% energy from fat; 0.1% energy from TFA), base diet with vaccenic acid (3.0% energy), base diet with mixed isomers of TFA from partially hydrogenated vegetable oil (3.0% energy), and base diet with cis-9, trans-11 CLA (1.0% energy). The added energy from TFA replaced energy from stearic acid. Participants were required to be between the ages of 25 and 65 years, have a body mass index between 20 and 38 kg/m(2), total cholesterol <280 mg/dl, fasting triacylglycerol <300 mg/dl, fasting glucose <126 mg/dl, and blood pressure <160/100 mm Hg (controlled with certain medications). Of the 116 participants who were randomized, a total of 95 completed the intervention. Results from this study will be important in determining whether ruminant TFA and industrially produced TFA differentially affect markers of cardiovascular risk, in the context of a highly controlled feeding study.