Benefits of CLA

Potential health benefits of CLA (conjugated linoleic acid) have been recorded in five major areas of study: cancer, immune system, atherosclerosis, diabetes, body composition and fat reduction.

Let's examine the evidence for the folowing health benefits of CLA:

• Cancer and Carcinogenesis Benefits of CLA
• Immune Function and Anti-Inflammatory Benefits of CLA
• Diabetes and Insulin Sensitivity Benefits of CLA
• Body Composition and Fat Reduction Benefits of CLA

Cancer and Carcinogenesis Benefits of CLA

There is evidence that CLA may help prevent several types of cancers including breast, skin, colorectal, lung, stomach, and prostate cancer.

The mechanism by which CLA defends against cancer is not well understood, but CLA appears to function, at least in part, as a potent antioxidant. It also seems to stimulate production of several types of immune cells.

The currently available cancer research on CLA has been conducted either in vitro or in mice, rats, and hamsters. To date, there have been no clinical trials with canine or human cancer patients examining the efficacy of CLA.

There are, however, human population studies associating increased dietary consumption of CLA with a decreased risk of breast cancer. There have also been studies correlating high intake of milk and milk fat, which is an excellent source of CLA, with a reduced breast cancer risk.

In an in vitro study of canine mammary tumor cells as well as non-cancerous mammary tissues collected from a dog with a malignant mammary tumor, "both t10,c12-CLA and c9,t11-CLA not only suppressed malignant mammary cell growth, but also exerted inhibitory effects on tumor-associated non-malignant mammary cells."

Both CLA isomers suppressed Prostaglandin E2 (PGE2) and cyclooxygenase 2 (COX-2) expression in normal and malignant canine mammary cells, with t10,c12-CLA having a greater effect on malignant mammary cells while c9,t11-CLA down-regulated COX-2 in normal and malignant mammary cells.

COX-2 is an enzyme that promotes inflammation, and COX-2 expression in mammary tumor cells is associated with a poor prognosis in human as well as canine cancers.

In most of the animal studies conducted to date, animals were fed CLA for two to five weeks before being exposed to a known carcinogen on one or more occasion. CLA supplementation continued throughout the study.

In rats, CLA supplementation has provided "significant protection against subsequent mammary tumor occurrence." In immunodeficient mice fed 1% of their diet as CLA before being inoculated with human breast adenocarcinoma cells, local tumor growth was reduced by up to 73% and the CLA "completely abrogated the spread of breast cancer cells to lungs, peripheral blood and bone marrow."

However, in a different study involving mice, CLA had no apparent effect on the growth of an already established, aggressive mammary tumor, even though CLA boosted certain aspects of the immune system. It is too early to say whether this may indicate that CLA is more useful as a cancer preventative than a cancer treatment.

Also, while CLA inhibited the proliferation of canine prostate cancer cells in vitro, it failed to prevent subcutaneous tumor growth when these canine prostate cancer cells were injected into immune-deficient mice.

There was no difference in tumor volumes between mice fed 1% CLA and the soybean oil control group, nor did CLA protect against metastasis. An almost identical study involving human prostate cancer cells did show a significant reduction in tumor size as well as metastasis.

Many veterinarians have been reluctant to suggest CLA for canine cancer patients because of its reputation as a weight loss supplement.

Weight loss is typically the last thing we want for canine patients, so this is clearly a concern.

However, several studies have shown that endotoxin-induced as well as cancer-induced cachexia was reduced in mice supplemented with 0.5% CLA.

Cachexia is the wasting syndrome that is associated with many cancers. CLA helped prevent anorexia and preserved muscle mass in tumor-bearing mice.

The endotoxin-induced cachexia study is particularly interesting in light of the fact that one of the other test groups in this study received a fish oil supplement.

Fish oil, a potent source of the omega-3 fatty acids DHA and EPA, is frequently prescribed for canine cancer patients.

Three groups of mice were injected with endotoxin: group one ate a basal diet without supplements, group two was fed the same basal diet with 0.5% fish oil, and group three was fed with the diet plus CLA.

Groups one and two lost twice as much weight as a result of cachexia as group three. In fact, the mice in the CLA group had body weights very similar to the vehicle-injected control group.

Immune Function and Anti-Inflammatory Benefits of CLA

Since immune function plays an integral role in cancer defense, these two categories are somewhat related. However, not all of CLA's cancer prevention benefits appear to be related to immune function; hence the separate categories.

CLA has been found to enhance immunologic function while protecting against some of the unwanted effects resulting from immune stimulation.

When immune cells are stimulated, they release cytokines to fight the cancer or infection, and some of these cytokines--tumor necrosis factor (TNF) and interleukin-1 (IL-1), for instance--can cause inflammation, fever, weight loss, and other unpleasant symptoms.

CLA appears to decrease TNF's catabolic effects on muscle, thereby reducing muscle wasting in cases of immune stimulation.

CLA supplementation has also been shown to increase interleukin-2 production and lymphocyte proliferation in several rodent studies.

A one-year human study on CLA supplementation found "a significant increase in the number of leukocytes." In another human study, CLA reduced levels of the pro-inflammatory cytokines TNF and IL-1, while increasing levels of the anti-inflammatory IL-10 in young, healthy subjects.

The anti-inflammatory benefits of CLA have been demonstrated in a number of animal studies and a few human studies involving a variety of inflammatory conditions including arthritis, lupus erythematosus, inflammation-driven colorectal cancer, inflammatory airway disease, antigen-induced histamine hypersensitivity, and bacterial-induced colitis.

There is evidence that CLA's ability to modulate inflammatory cytokines may also have positive effects on bone health. Several animal and in vitro studies have shown promising results regarding reduced bone loss and improved bone formation.

While studies examining immune benefits of CLA have been overwhelmingly positive, at least one human study has correlated CLA supplementation with negative events.

In a study of immune outcomes in healthy humans, test subjects received an enriched single isomer CLA supplement (either cis-9,trans-11 CLA or trans-10,cis-12 CLA).

Both CLA isomers resulted in dose-dependent reductions in the mitogen-induced activation of T lymphocytes, although lymphocyte subpopulations were not affected.

Diabetes and Insulin Sensitivity Benefits of CLA

The insulin and glucose related benefits of CLA are controversial. Initial research suggested that CLA can increase insulin sensitivity and improve glucose tolerance.

More recently, however, there have been a few human studies demonstrating a disturbing increase in insulin resistance.

While the subject certainly warrants further study, some researchers have pointed out that studies noting an increase in insulin resistance either used single isomer t10,c12-CLA supplements, or they were of short duration.

It appears that CLA supplementation may cause a transient increase in insulin resistance seen in studies conducted over a 4 to 12 week period that disappears after 14 to 18 weeks of supplementation.

In longer term studies using a commercially available mixed isomer CLA supplement, effects on insulin and glucose are, at worst, neutral.

Body Composition and Fat Reduction Benefits of CLA

No other area of CLA study has inspired as much research as weight loss and fat reduction. Indeed, almost all CLA supplements are marketed primarily as weight loss or muscle building aids.

You can also read more about CLA and Weight Loss.

Dozens of animal and human studies have been conducted on the fat loss benefits of CLA, but while rodents experienced a fat reduction up to 70% in a short time frame, human and canine studies have shown far more modest results.

While often promoted as a weight loss supplement, CLA does not produce a significant loss of body weight--not even in rodent studies.

CLA does, however, have an effect on body composition, reducing body fat--particularly in the abdominal area--and slightly increasing lean body mass.

It also appears to generate a small elevation in resting metabolic rates. Individuals gaining weight while taking CLA supplements typically see an increase in lean body mass and a decrease in body fat when compared to placebo groups.

Although the majority of studies clearly demonstrate that CLA affects body composition, that effect is small in humans and dogs. On average, human CLA studies have shown a modest fat reduction of 0.09 kg per week.

That's a loss of two pounds of body fat in ten weeks. While it may not sound like much, consider that the average human and the average dog are both getting fatter every year.

In the United States, people gain an average of about a pound every year. CLA may has the potential to replace the annual weight gain experienced by many with a modest reduction in body fat.