Conjugated linoleic acid (CLA), is the broader term used to describe a mixture of different forms of linoleic acid. Discovered by chance in 1978 by Michael W. Pariza, CLA naturally occurs in small amounts in the meat and dairy products of ruminant animals; that is, animals that chew their cud, such as cows, goats, and sheep, among others. Though research of CLA has yielded conflicting findings, early studies have suggested some potential health benefits related to cancer, heart disease, diabetes, kidney disease, bone density, and obesity.
CLA cannot be produced in great quantity by the human body. Instead, people obtain this naturally-occurring fat from dairy animals that have the ability to convert linoleic acid from plant material into CLA because of microorganism activity in the rumen. As a result of a few initial studies on the health benefits of CLA, particularly the effect CLA may have on fat storage, people have started using man-made forms of CLA as a supplement to their diet.
Following its discovery, other studies have been conducted to examine the beneficial effects of CLA on cancer, immune functions, and atherosclerosis. A variety of antioxidant and anti-tumor properties have also been linked to CLA, and select studies on mice and rats have shown promising results in reducing tumor growth, particularly in breast, skin, and colon tumors.
Does it really reduce body fat?
What has arguably generated the most noise in the health community is the possibility that CLA may be useful in reducing body fat. But whether CLA is an effective dietary supplement has not been fully proven, and the way that CLA may work to decrease body fat is still unclear.
When early animal studies showed CLA to have convincing results of reducing fat, researchers were optimistic that the same results may also apply to humans. A Norwegian study conducted in 1997 concluded that although people taking CLA lost very little body weight, their lean muscle mass increased in proportion to the amount of fat they lost. Since then, other studies have produced inconsistent and often less significant results. One recent study in particular, published in the American Journal of Clinical Nutrition in May of 2007, analyzed previous human studies and concluded that CLA may only produce a modest loss in body fat in humans at 3.2 g per day.
How CLA may have some potential benefits on obesity may be a result of decreased energy and food intakes; decreased fat storage; and increased energy expenditure, fat breakdown, and fat burning (oxidation). It is also important to note that any increase in lean muscle can also be attributed to a more efficient metabolism and an increase in the amount of calories burned. Dr. Pariza commented that based on his research, he believes CLA can prevent existing fat cells from growing, but not prevent new fat cells from being formed. Additionally, he believes CLA may make it easier for people to stay on their diets.
At this point, not enough is known about how much CLA (i.e., the dose) is needed for it to be effective as a dietary supplement, or whether any side effects are caused by using CLA. The 2007 analysis does confirm the results of an earlier 2000 study that found that approximately 3.4 g of CLA per day was needed to obtain the beneficial effects of CLA on body fat. Likewise, there is concern regarding controversial evidence that suggests the use of CLA by overweight people may increase insulin resistance and may possibly increase their risk of developing diabetes. Again, there is no evidence to prove an effective dose of CLA or any risks involved in using it.
Preliminary research on the benefits of CLA as a dietary supplement is still very limited. Its effect on reducing fat is more convincing in animal studies than in human studies. While some studies do show a positive relationship between using CLA and decreases in body fat, the overall evidence is not conclusive. Safety and toxicity levels have yet to be established, and other benefits associated with using CLA are not clearly defined. For now, using CLA as a dietary supplement is solely at the discretion of the consumer.