CLA, ( Conjugated linoleic acid) for Precention of Cancer and Obesity

Peter Ou, Ph.D. Colorectal cancer. Epidemiological research in women suggests that high dietary intake of conjugated linoleic acid (CLA) might reduce the risk of colorectal cancer by up 39% (13775). It is not known if taking CLA supplements is associated with a reduced risk of colorectal cancer.

Breast cancer. There is preliminary evidence that CLA might help reduce the risk of breast cancer. Postmenopausal women who have a higher intake of CLA in foods, particularly cheese, seem to have a lower risk of developing breast cancer (5058). More evidence is needed to rate CLA for this use.

Obesity. Taking CLA orally seems to improve body composition in patients who are overweight or obese. Taking 0.7 to 4.5 grams/day seems to significantly decrease body fat mass (BFM) and might increase lean body mass (LBM) in some patients. But CLA does not seem to reduce total body weight or body mass index (BMI) (2819,2821,3153,4947,10410,13137). CLA also seems to reduce hunger and improve satiety and feeling of fullness, but this appetite suppression does not necessarily result in a lower energy intake or improved body weight maintenance (11327). There is evidence that the isolated trans-10, cis-12 isomer of CLA can increase hyperproinsulinemia and insulin resistance in patients with abdominal obesity (2821,13026,13137). Hyperproinsulinemia is an independent risk factor for type 2 diabetes and cardiovascular disease. Therefore, CLA might not be a good choice for obese patients; however, most commercial CLA products contain a mixture of CLA isomers. It is not known if these mixed CLA isomer products have this same risk.

Mechanism of Action:

Conjugated linoleic acid (CLA) refers to a group of conjugated dienoic isomers of linoleic acid, including cis-9, trans-11 linoleic acid and trans-10, cis-12 linoleic acid. Different isomers seem to have different physiological effects (3158,13069). Dairy products and beef are the major dietary sources. Food sources provide both isomers, but typically contain more of the cis-9, trans-11 isomer in a ratio of 30-70:1. Supplements containing CLA usually provide the two isomers in a 50:50 ratio (13069).

Plant oils contain only small amounts of CLA. Plant oils are good sources of linoleic acid, but in humans linoleic acid does not seem to be converted to CLA in significant amounts (5933,13069).
Conjugated linoleic acid can also be produced synthetically by exposing oils rich in linoleic acid, such as safflower and soybean, to a base and heat. This CLA product is high in both the cis-9, trans-11 and the trans-10, cis-12 isomers (3001).

There is a lot of interest in using CLA for weight loss in obesity. Researchers think that CLA might reduce body fat deposits by promoting apoptosis in adipose tissue (3070,5928).
There is some evidence that only the trans-10, cis-12 isomer has an effect on body fat mass (3001). Additional evidence, however, shows the isolated trans-10, cis-12 isomer might also cause hyperproinsulinemia, increase insulin resistance and glycemia, reduce HDL cholesterol in men with abdominal obesity, and increase lipid peroxidation and C-reactive protein (CRP) levels (2821,13026,13137).
There is also interest in using CLA for cancer prevention. Preliminary evidence suggests CLA may be cytotoxic to human breast cancer cells. It may also inhibit the proliferation of human malignant melanoma and colorectal cancer cells (8997).
CLA appears to enhance immune function (5926,5934), increase peripheral blood mononuclear cell production (2810), and inhibit cyclooxygenase and lipoxygenase pathways in tumor cells (5926,5934). CLA might also modulate cellular response to tumor necrosis factor-alpha (TNF-alpha) (5924).
Adverse Reactions:

Orally, the most common adverse effect of conjugated linoleic acid is gastrointestinal upset including diarrhea, nausea, loose stools, and dyspepsia (3153,4947). In some cases patients can experience fatigue (3153

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