Food Lipids: Chemistry, Nutrition, and Biotechnology

or
� plasma total cholesterol (mmol/L) = 0.03 � (2 � �Sat� � �Poly)
� plasma total cholesterol (mg/dL) = 1.2 � (2 � �Sat� � �Poly)
where Sat� are the percentages of energy provided by saturated fatty acids with 12,
14, or 16 carbon atoms (lauric, myristic, and palmitic acid, respectively), whereas
Poly refers to the amount of polyunsaturated fatty acids in the diet.
How should this formula be interpreted? First, it should be realized that effects
are expressed relative to those of carbohydrates. A hypercholesterolemic fatty acid
is therefore defined as a fatty acid that causes an increase in the plasma cholesterol
level when substituted in the diet for an isocaloric amount of carbohydrates. Thus,
when 10% of energy from Sat� is replaced by carbohydrates, �Sat� equals �10, and
the expected decrease in plasma total cholesterol concentrations is 0.03 � 2 ��10
= �0.60 mmol/L [�24 mg/dL]. If this amount of carbohydrates is then replaced by
linoleic acid, a further decrease of �0.03 � 10 = �0.30 mmol/L [�12 mg/dL] is
expected. Direct replacement of Sat� by Poly will yield the sum of these two effects,
a fall of 0.90 mmol/L [36 mg/dL]. Further, this formula suggests that—because they
are no part of the equation—the effects on plasma total cholesterol concentrations
of saturated fatty acids with fewer than 12 carbon atoms, of stearic acid, and of
monounsaturated fatty acids are similar to those of carbohydrates. Finally, it can be
seen that the cholesterol raising effect of Sat� is about twice the cholesterol lowering
effect of Poly.
Similar types of studies were carried out in the 1960s by Hegsted and colleagues
[6]. Results were essentially similar, but it was also concluded that myristic
acid was more cholesterolemic than palmitic and lauric acids.
These and other studies have lead to recommendations that the most effective
diet for lowering plasma total cholesterol concentration should contain a low proportion
of the cholesterol-raising saturated fatty acids and a high proportion of linoleic
acid. Also, a reduction in cholesterol intake was advocated as dietary cholesterol
increases plasma total cholesterol concentrations [6,7].
However, these earlier well-controlled studies were not specifically designed to
examine the effects of specific dietary fatty acids on plasma cholesterol concentrations
and over the various lipoproteins. Therefore, new studies were initiated that
compared side-by-side effects of specific fatty acids on the plasma lipoprotein profile.
B. Recent Studies
1. Saturated Fatty Acids
To discuss the effects of saturated fatty acids on plasma lipid and lipoproteins, the
saturated fatty acids, in agreement with the results of Keys and colleagues [5], fall
into three classes: medium chain fatty acids; fatty acids with 12, 14, or 16 carbon
atoms; and stearic acid.
a. Medium Chain Fatty Acids. Saturated fatty acids with fewer than 12 carbon
atoms are called short and medium chain saturated fatty acids (MCFAs) and are
found in relatively large amounts in coconut fat, palm kernel oil, and butterfat, but
also in certain structured lipids, parenteral nutrition preparations, and sport drinks.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.