Food Lipids: Chemistry, Nutrition, and Biotechnology

fatty acids from fish oils, however, have different effects. In normocholesterolemic
subjects, these fatty acids do not change plasma LDL or HDL cholesterol concentrations,
but do lower plasma triacylglycerols and the concentration of cholesterol in
VLDL [26]. In hyperlipidemic subjects, and in particular in patients with elevated
triglyceride concentrations, fish oils also lower plasma triacylglycerols, but raise LDL
and HDL cholesterol concentrations [27].
4. trans Fatty Acids
Most unsaturated fatty acids found in nature have the cis configuration. This means
that the two carbon side chains attached to the double bond point into the opposite
(cis) direction. However, in some fatty acids the carbon side chain point into the
same (trans) direction. In this way, two compounds are formed that have exactly the
same number and type of atoms, but have different chemical, physical, and physiologic
characteristics.
trans Fatty acids are formed when vegetable oils are hardened by hydrogenation.
These hydrogenated fats are used for the production of certain types of margarines,
frying fats, and foods prepared with these fats. Most trans fatty acids in the
diet have 18 carbon atoms and one double bond (trans-C18:1). However, trans fatty
acids are not only found in hydrogenated oils but also in milk fat and body fat from
ruminants, formed from dietary polyunsaturated fatty acids by the action of bacteria
in the rumen of these animals. The trans polyunsaturated fatty acids in the diet mainly
originate from hydrogenated fish oils.
a. trans Fatty Acids. LDL cholesterol concentrations increase when cis-monounsaturated
fatty acids in the diet are replaced by trans-monounsaturated fatty acids
[28]. In most studies, a decrease in HDL cholesterol was also observed. Although
the LDL cholesterol raising effect of trans-monounsaturated fatty acids is less than
the effect of a mixture of saturated fatty acids, trans-monounsaturated fatty acids
also lowered HDL cholesterol relative to a mixture of saturated fatty acids. Therefore,
it was concluded that both types of fatty acids have an unfavorable effect on the
plasma lipoprotein profile [29] (Fig. 8).
C. Conclusion
Dietary fatty acid composition affects the distribution of cholesterol over LDL and
HDL. As compared with an isoenergetic amount of carbohydrates, myristic acid
(C14:0) is the most potent plasma total and LDL cholesterol–raising saturated fatty
acid. From the other saturated fatty acids in the diet, lauric acid (C12:0) and, to a
lesser degree, palmitic acid (C16:0), also have a hypercholesterolemic effect, whereas
stearic acid (C18:0) seems to be neutral. Linoleic (cis,cis-C18:2) and probably also
oleic acid (cis-C18:1) have a small LDL cholesterol–lowering effect. trans Fatty
acids have a strong plasma total and LDL cholesterol–increasing effect. Effects on
LDL cholesterol levels are positively related to those on HDL cholesterol concentrations.
An exception are trans fatty acids that do not have an effect on HDL as
compared with carbohydrates. Thus, a reduction in the intake of the cholesterolraising
saturated fatty acids and trans fatty acids is more important for optimizing
the plasma lipoprotein profile than a reduction in total fat intake per se.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.