09.12.2012 Views

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

stearic) had been incorporated by interesterification. They found no differences. Earlier<br />

a similar study had been carried out in rabbits with no effects on cholesterolemia<br />

or atherosclerosis [52].<br />

During the r<strong>and</strong>omization process the structure of fats is changed so that each<br />

component fatty acid is present in each position of the triglyceride at one-third of<br />

its total concentration. This change appears to influence the atherogenicity of a fat.<br />

Tallow <strong>and</strong> lard each contain about 24% of total fatty acid as palmitic acid. In lard<br />

more than 90% of the component palmitic acid is at the 2-position of the triglyceride<br />

whereas in tallow no more than 15% is. Lard is significantly more atherogenic for<br />

rabbits than tallow. When the fats are r<strong>and</strong>omized each contains 8% of palmitic acid<br />

at the 2-position <strong>and</strong> they are of equivalent atherogenicity [53] (Table 3). Studies<br />

with r<strong>and</strong>omized cottonseed oil [54] or palm oil [55] <strong>and</strong> with synthetic triglycerides<br />

[56] all indicate that increased presence of palmitic acid at the 2-position of a triglyceride<br />

enhances its atherogenic effect. There are no differences in serum lipids<br />

or in lipoprotein size in sera of rabbits fed native or r<strong>and</strong>omized fat, nor are serum<br />

lipids affected. Since presence of palmitic acid at 2-position increases fat absorption<br />

[57,58], perhaps feeding fats with palmitic acid at the 2-position is the equivalent of<br />

a higher fat diet.<br />

Every decade concern surfaces about the atherogenic effects of fats containing<br />

trans unsaturated double bonds (trans fat). The trans fats are generally metabolized<br />

in a manner similar to that of their cis counterparts. They accumulate in tissues upon<br />

feeding <strong>and</strong> disappear relatively soon after cessation of feeding [59,60]. In rabbits<br />

they lead to increased cholesterolemia but not more severe atherosclerosis; this is<br />

true in rabbits fed cholesterol [61] or a cholesterol-free atherogenic diet [62]. In men<br />

fed diets high in elaidic acid Lp(a) levels are increased [63,64], but this effect is not<br />

seen when the dietary trans fat is low in elaidic acid [65,66]. These findings suggests<br />

specific metabolic roles for specific trans-fatty acids. In rats trans fats exert no deleterious<br />

effects if the diet contains sufficient levels of linoleic acid [67]. In man, the<br />

Table 3 Influence of Native <strong>and</strong> R<strong>and</strong>omized Tallow <strong>and</strong> Lard on Atherosclerosis<br />

in Rabbits<br />

Tallow<br />

Group<br />

R<strong>and</strong>omized<br />

tallow Lard<br />

R<strong>and</strong>omized<br />

lard<br />

No. 7/8 7/8 8/8 8/8<br />

% 16:0 at SN2 3.7 a<br />

8.5 a<br />

20.8 b<br />

7.6 b<br />

Plasma<br />

Cholesterol (mg/dL)<br />

Aorta<br />

1177 � 156 1189 � 166 926 � 184 834 � 153<br />

Arch 1.29 � 0.24 1.50 � 0.53 2.69 � 0.28 c<br />

1.50 � 0.28 c<br />

Thoracic 0.79 � 0.26 0.79 � 0.28 1.75 � 0.28 d<br />

0.69 � 0.19 d<br />

a Of 24.8% total.<br />

b Of 21.4% total.<br />

c Graded on 0–4 scale.<br />

d Lard vs. r<strong>and</strong>omized lard.<br />

Note Rabbits were fed semipurified diet containing 0.4% cholesterol for 60 days. (p =

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!