Food Lipids: Chemistry, Nutrition, and Biotechnology

0.1% to 0.9% CLA for 2 weeks before infusing with WAZ-2T metastatic mammary
tumor cells into the right inguinal mammary gland did not affect mammary tumor
latency, tumor incidence, or volume. Therefore, dietary CLA might be less effective
on the growth of an established and aggressive mammary tumor.
The anticarcinogenic effects of CLA isomers have been exclusively tested in
animal models and cell culture systems. There is no direct evidence that these fatty
acids protect against carcinogenesis in the human. The most promising evidence to
date that dietary sources of CLA are beneficial is from epidemiological studies that
link milk consumption to reduced breast cancer. In one recent study, Knekt et al.
(86) found a significant inverse relationship between milk intake and breast cancer
incidence among 4697 initially cancer-free Finish women over a 25-year follow-up
period. It was found that the risk of breast cancer was halved in women who consumed
more than 620 mL milk per day compared with those consuming less than
370 mL/day and suggested that CLA was the active component. The average amount
of CLA in milk is approximately 10 mg/g of milk fat. Based on the average fat
content of 35 g/L of milk (87), the daily intake of CLA for these women could be
217 mg for those consuming 620 mL milk per day and 130 mg for those consuming
370 mL milk per day. However, the calculated CLA intake level for these women is
still far below the estimated CLA level of 1 g/day that would be significant for
cancer prevention (53). The results from the epidemiological studies and reduced
incidence of breast cancer could suggest that dairy fats contain other factors that
reduce cancer risk or other lifestyle and dietary factors associated with these populations,
e.g., fish intake (n-3 fatty acids), that would influence cancer incidence.
Experiments designed for investigating the role of CLA in human cancer are needed
to identify the relationships between these fatty acids and other lifestyle factors
contributing to lower cancer risk.
B. Cardiovascular Disease
The potential health benefits of CLA may extend beyond cancer to the prevention
of congestive cardiovascular diseases since these fatty acid isomers were shown to
reduce atherogenesis in animal studies (63,64). Lee et al. (63) assessed the effect of
CLA on atherosclerosis in rabbits by supplementing 0.5 g per animal per day for 22
weeks. In comparison with control rabbits that were given a similar diet containing
14% fat and 0.1% cholesterol without CLA, total and LDL cholesterol and triacylglycerol
(TAG) levels in blood were markedly lower in those given CLA. At the
same time, the ratio of LDL cholesterol to HDL cholesterol and ratio of total cholesterol
to HDL cholesterol were significantly reduced in the group given CLA.
Rabbits given CLA also showed less atherosclerosis in the aorta. In another study
by Nicolosi et al. (64), CLA effects on plasma lipoproteins and aortic atherosclerosis
were examined. Fifty hamsters were divided into five groups of ten and given 0
(control), 0.06 (low), 0.11 (medium), and 1.1 (high) percentage of total dietary energy
of CLA or 1.1% of total energy as LA. Animals given the CLA-containing diets
collectively had significantly reduced levels of plasma total cholesterol, non-HDL
cholesterol (combined VLDL and LDL) and triacylglycerols with no effect on HDL
cholesterol, in comparison with the controls. For the CLA treatment, a tocopherol
sparing effect was observed compared to the control group. Morphometric analysis
of aortas revealed less early atherosclerosis in the CLA-treated hamsters compared
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