Health effects of CLA versus industrial trans fatty acids

High intakes of trans fatty acids increase the risk of coronary heart disease
and authorities worldwide are attempting to limit their intake. However, there
are two sources of trans fatty acids with possibly different effects on health.
So-called *industrial* trans fatty acids are produced by partial hydrogenation
of vegetable and fish oils. The unfavourable effects of these trans fatty acids
are well established: they raise LDL-cholesterol, depress HDL cholesterol, and
are associated with increased coronary heart disease (fig. 1A) [Ascherio,
1999]. Trans fatty acids also occur naturally in the dairy and body fat of
ruminant animals including cows, and these ruminant trans fatty acids are now
the dominant form in the European diet. The effects of dairy trans fatty acids
on blood lipids in humans have not been studied, and their intake is associated
with less rather than more coronary heart disease in several studies (fig. 1B)
[Willett WC, 1993; for a review see Weggemans, 2004]

To investigate what the effect is of CLA on blood lipoproteins, inflammatory
markers, blood pressure and insulin status in human volunteers relative to
industrial trans fatty acids and to oleic acid

It will be a double-blind randomized multiple cross-over trial with 3
treatments:
• CLA
• industrial trans fatty acids (as a positive control)
• oleic acid (Cis 18:1, the monounsaturated fatty acid in unhydrogenated
vegetable oils) as a reference fat.
Each volunteer receives each diet for three weeks, in random order, for a total
of 9 weeks. Three weeks is sufficient to reach new stable lipoprotein levels.

It will be a double-blind randomized multiple cross-over trial with 3
treatments:
• CLA
• industrial trans fatty acids (as a positive control)
• oleic acid (Cis 18:1, the monounsaturated fatty acid in unhydrogenated
vegetable oils) as a reference fat.
Each volunteer receives each diet for three weeks, in random order, for a total
of 9 weeks. Three weeks is sufficient to reach new stable lipoprotein levels.
Location: Wageningen University, Division of Human Nutrition, the Netherlands.
Almost all food (90% of energy) is provided to the participants, as described
earlier [Mensink, 1990]. Duplicate blood samples are taken in the last week of
each dietary period.
The margarines will be produced and coded with random codes by NIZO so that the
study will be double-blind. Analyses of the margarines before the trial will
also be blinded. The codes will be broken only after the data have been
analysed and all authors have agreed on the essential tables and figures.

The risks are low, burden is quite heavy because the subjects have to eat the
provided food for 9 weeks. However, it is a normal, nice eatable diet.