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

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

with the control group. Interestingly, the LA treatment showed a similar effect compared<br />

with CLA in this study. Yeung et al. (88) reported that by feeding hamsters<br />

20 g/kg dietary linoleic acid or CLA, serum total fasting cholesterol <strong>and</strong> triacylglycerol<br />

were significantly reduced compared with the control which had no fatty<br />

acid supplementation. However, the cholesterol-lowing mechanism for LA <strong>and</strong> CLA<br />

appeared to be different. CLA lowered the activity of intestinal acyl CoA–cholesterol<br />

acyltransferase (ACAT) while LA had no effect on this enzyme, indicating that CLA<br />

could affect the absorption of dietary cholesterol. In rats fed (up to 1.5% dietary<br />

CLA for 60 days) the ratio of HDL cholesterol/TC <strong>and</strong> serum TAG concentrations<br />

were significantly elevated (89). These studies showed that CLA was hypocholesterolemic<br />

<strong>and</strong> antiatherogenic; however, a recent experiment using C57BL/6 mice<br />

given atherogenic diets with added CLA (0.5% <strong>and</strong> 0.25% of the diet) demonstrated<br />

increased development of aortic fatty streaks despite a change in serum lipoprotein<br />

profiles that could be considered less atherogenic (90).<br />

There is currently no conclusive evidence that CLA protects against early atherogenesis.<br />

It was initially proposed that CLA was able to protect LDL particles from<br />

oxidation (54,55,63,64); however, a recent in vitro investigation by ven den Berg et<br />

al. (21) showed no antioxidant properties attributable to CLA. Also, CLA showed<br />

its positive effect on atherosclerosis in rabbits but not in mice, which could indicate<br />

a species difference for the response to dietary CLA supplementation.<br />

Benito et al. (52) showed that although CLA isomers were incorporated into<br />

platelet lipids, antithrombotic properties, such as blood clotting parameters <strong>and</strong> in<br />

vitro platelet aggregation, were not affected by daily supplement of 3.9 g CLA to a<br />

typical Western diet for 63 days in healthy adult females.<br />

In a human study involving 17 female subjects, CLA was given as a dietary<br />

supplement at 3.9 g/day for 93 days. Blood cholesterol or lipoprotein levels were<br />

not altered by CLA supplementation in healthy <strong>and</strong> normolipidemic subjects. In this<br />

investigation the short-term supplementation with CLA did not afford health benefits<br />

for the prevention of atherosclerosis (20).<br />

C. Body Fat <strong>and</strong> Lipid Metabolism<br />

Numerous studies in growing animals demonstrated that CLA reduced fat deposition<br />

<strong>and</strong> increased lean body mass (69–71, 91–94). When CLA (0.5–1% of diet) was<br />

given to AKR/J male mice (39 days old), it produced a rapid <strong>and</strong> marked decrease<br />

in fat accumulation <strong>and</strong> an increase in protein accumulation without any major effects<br />

on food intake (69). Park et al. (93) provided diets with a lower dietary CLA level<br />

(5% corn oil � 0.5% CLA) to 6-week-old ICR mice <strong>and</strong> observed a significantly<br />

reduced body fat content by 57% (male) <strong>and</strong> 60% (female), <strong>and</strong> increased lean body<br />

mass relative to control mice that were given a diet containing 5.5% corn oil. Similar<br />

effects of CLA on body fat accumulation were shown in rats. Yamasaki <strong>and</strong> colleagues<br />

(70) studied the effect of CLA on liver <strong>and</strong> different adipose tissues in 4week-old<br />

male rats given diets (AIN-93G with 7% safflower oil as a control) containing<br />

1% <strong>and</strong> 2% dietary CLA (at the expense of the safflower oil) for 3 weeks.<br />

They observed reduced levels of TAGs <strong>and</strong> nonesterified fatty acids in the liver <strong>and</strong><br />

white adipose tissue without significant changes in lipids of brown adipose tissue.<br />

In another study, Yamasaki et al. (95) reported that dietary CLA treatments (0%, 1%,<br />

<strong>and</strong> 2% of the diet) dose-dependently accelerated the release of lipids in white adi-<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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

Saved successfully!

Ooh no, something went wrong!