The Effects of Natural Versus Man-Made Trans Fatty Acids on Lipoprotein Profiles: A Pilot Study

The purpose of this study is to test the effects of natural vs. man-made trans fatty acids (trans fats) on blood cholesterol.

Since the purpose of the study is to determine the statistical power required for a definitive study testing and comparing the effects of two trans fatty acids, vaccenic and elaidic acid, on lipoprotein profiles, no hypotheses will be specified.

Specific Aims:

1. To determine the variability in the lipid and lipoprotein response to diets enriched in natural versus man-made trans fats in order to appropriately power a larger scale clinical study
2. To optimize the delivery of trans fat-enriched diets through the development of supplemental food items

The adverse health effects of trans fatty acids (TFA) on cardiovascular disease (CVD) risk have been established in a number of metabolic and epidemiological studies \[Willett 1993, Hu 1997, Ascherio 1996, Pietinen 1997, Oomen 2001\]. Trans fats are fatty acids with 18 carbon chains and one or more double bond(s). The hydrogen atoms of the double bond(s) are in a configuration (trans rather than cis) that results in the straightening of a normally kinked unsaturated fatty acid chain. Trans fats occur naturally in low quantities in dairy and beef products, but have also been artificially introduced to the food supply by the process of the hydrogenation of vegetable oils \[Mann 1994\]. Only two studies linking the consumption of trans fatty acids with an increased risk of CVD have distinguished between the effects of man-made versus naturally occurring trans fatty acids \[Willett 1993, Oomen 2001\].

It has been suggested that the relationship between trans fatty acids and coronary heart disease is specifically attributable to man-made trans fatty acids. In fact, some of the trans fats that occur naturally in animal products, in particular, conjugated linoleic acid (CLA), may have beneficial health effects. CLA has been shown to be anti-carcinogenic \[Ip 2003\], anti-atherogenic \[McLeod 2004\] and anti-diabetic \[Rainer 2004\]; it has also been shown to enhance the immune response and have positive effects on growth and energy partitioning. As a precursor to CLA, vaccenic acid (VA), another trans fatty acid found in dairy and beef products, may also provide health benefits. Bioconversion of VA to CLA has been recently demonstrated \[Turpeinen 2002\]. The effects of diet supplementation with VA on health parameters have yet to be defined.

The objective of the overall research project will be to test the hypothesis that the ingestion of high doses of naturally occurring VA does not cause the adverse lipid and lipoprotein effects known to occur with the consumption of man made trans fatty acids, in particular, elaidic acid (EA). The latter is the primary trans fatty acid found in products such as margarines, cakes, cookies, crackers and other baked and processed foods \[Steinhart 2003\]. The primary outcome measure will be the ratio of total to high density lipoprotein (HDL) cholesterol. Related secondary outcome measures include concentrations of low density lipoprotein (LDL) cholesterol, HDL cholesterol, triglyceride (TG) and Lp(a). The present proposal is designed to test the feasibility of, and determine the power for, a definitive study.

Eligibility Criteria:
Inclusion Criteria:

* Male
* Age \>= 18 years
* Body mass index (BMI) less than 35 kg/m\*m
* Fasting total cholesterol and LDL cholesterol less than the 95% for age and sex
* Fasting triglyceride \<= 400 mg/dl
* Fasting blood glucose \<= 125 mg/dl
* Fasting thyroid stimulating hormone less than 0.3 or greater than 5.0 uIU/ml
* Blood pressure \<= 150/90
* Agrees to no alcohol during the study
* Agrees to maintain same level of physical activity throughout the study

Exclusion Criteria:

* Smokers
* Personal history of coronary heart disease, cerebrovascular disease or vascular disease, diabetes, bleeding disorder, liver or renal disease, or of cancer (other than skin cancer) in the last five years.
* Use of drugs known to affect lipid metabolism, blood thinning agents, or hormones.