The Impact of CLA
The impact of conjugated linoleic acids (CLA) on health is an active area of research worldwide. This minor component of ruminant fat could be endowed with a great potential benefit to our health.
CLA is more powerful than any other fatty acid in modulating tumour development.1 In fact, isomers of CLA are the only natural fatty acids to exhibit consistent anti-tumour properties at levels of 1.0% or less of total fats in the diet.2 You’d need about 10 times more fish oil and its omega-3 fats to achieve similar benefits.1 CLA is not included on the Nutrition Facts table because it does not fit into the trans fat definition. Health Canada recognizes that trans CLA may have different biological effects than other trans fats.
What Animal Studies are revealing
Until recently, studies conducted on animal models used commercial CLA mixtures. Unlike the CLA in ruminant fats, this mixtures contained equal quantities of c-9,t-11 CLA and t-10,c-12 CLA. It was found to cause a dose-dependent reduction in the incidence and number of mammary tumours.1 CLA fed to animals prepuberty offered life-long protection against mammary cancer.3 However, once the mammary gland achieved maturity, CLA had to be fed continuously to achieve the same effect.3 More recently, natural CLA-enriched butter was not only as effective as commercial CLA mixtures, it was preferentially stored in adipose tissue.4 Further studies have confirmed that vaccenic acid, by virtue of its conversion to c-9,t-11 CLA,5 virtually doubles tissue content of CLA.6
What Human Studies are revealing
The findings to date from research in humans, still in its infancy, suggest that CLA may protect against breast cancer in women.7-11 For example, a recent study of postmenopausal women demonstrated that those with the highest intake of CLA-rich dairy foods, particularly cheese, had higher levels of CLA and vaccenic acid in their blood and, more important, about a 70% lower risk of breast cancer.9 Interestingly, another study demonstrated that even when CLA intake was too low (~155 mg) to impact overall breast cancer risk, it retarded the development of the more aggressive, estrogenreceptor negative tumours in premenopausal women, thereby potentially reducing the burden of breast cancer.11
How Much CLA is Enough?
No one knows for certain. If we consider only CLA from natural sources, short-term animal studies suggest an equivalent daily intake of c-9,t -11 CLA of about 1.5 g.12 However, we know that c-9,t -11 CLA is metabolized in the body and can be stored. Future studies will determine how much individuals who regularly consume CLA rich dairy and meat really need to ensure protection against cancer.
CLA Content of Selected Foods from Ruminants*
| Food (serving) | mg CLA/ g fat | mg fat/ serving | mg CLA/ serving |
|---|---|---|---|
| Whole milk* (250 ml) | 3.4 | 8.6 | 29.2 |
| Butter (10g) | 4.7 | 8 | 37.6 |
| Plain yogurt (>4% MF;175g) | 4.4 | 10 | 44 |
| Cheddar cheese (50g) | 4.2 | 17 | 71.4 |
| Mozzarella cheese (50g) | 4.6 | 13 | 59.8 |
| Lean ground beef (75g, broiled) | 1.8 | 10.3 | 18.5 |
| Rib roast (100g, cooked) | 2.9 | 26.75 | 77.6 |
* CLA content varies with the season and the diet of the animal.
References
- Ip C et al. 1994. CLA, a powerful anticarcinogen from animal fat sources. Cancer 74:1050-1054.
- National Research Council. 1996. Carcinogens and Anticarcinogens in the Human Diet. National Academy Press, Washington, DC.
- Thompson HJ et al. 1997. Morphological and biochemical states of mammary gland as influenced by conjugated linoleic acid: implication for a reduction in mammary cancer risk. Cancer Res 57:5067-5072.
- Ip C et al. 1999. Conjugated linoleic acid-enriched butter fat alters mammary gland morphogenesis and reduces cancer risk in rats. J Nutr 129:2135-2142.
- Lock AL et al. 2004. The anticarcinogenic effect of trans-11 18:1 is dependent on its conversion to cis-9,trans-11 CLA by a desaturate in rats. J Nutr 134:2698-2704.
- Lock AL et al. 2005. The biology of trans fatty acids: Implications for human health and the dairy industry. Aust J Dairy Technol 60:3-12.
- Knekt P et al. 1996. Intake of dairy products and the risk of breast cancer. Br J Cancer 73:687-691.
- Pryor M et al. 1989. Adolescent diet and breast cancer in Utah. Cancer Res 49:2161-2167.
- Aro A et al. 2000. Inverse association between dietary and serum conjugated linoleic acid and risk of breast cancer in postmenopausal women. Nutr Cancer 38:151-157.
- Hjartåker A et al. 2001. Childhood and adult milk consumption and risk of premenopausal breast cancer in a cohort of 48,844 women - the Norwegian Women and Cancer Study. Int J Cancer 93:888-893.
- McCann SE et al. 2004. Dietary intake of conjugated linoleic acids and risk of premenopausal and postmenopausal breast cancer, Western New York Exposures and Breast Cancer Study (Web Study). Cancer Epidemiol Biomarkers Prev 13:1480-1484.
- Parodi PW. 2004. Milk fat in human nutrition. Aust J Dairy Technol 59:3-59.
Keywords: conjugated linoleic acid
Nutrients in Milk Products Keywords
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