Conjugated Linoleic Acid (CLA) is a polyunsaturated, conjugated fatty acid that is a natural part of the human diet, found primarily in meat and dairy products. CLA is a trans-fat (which are thought to increase the risk of coronary heart disease). 1
However, it is claimed that conjugated linoleic acid is not harmful in the same way as other trans fatty acids, but rather is beneficial. CLA is primarily found in the meat and dairy product of ruminants (i.e. cattle, goats, sheep, etc.), especially those that have been grass-fed.2
CLA is thought to be a natural dietary supplement that induces a combination of fat loss and muscle gain. The benefits of conjugated linoleic acid are believed to include:
- Decrease in fat
- Increase in muscle growth
- Increase in metabolic rate
- Protects against fat gain following weight loss, thus maintaining initial reductions in body fat and weight, in the long-term.
- May lower cholesterol and triglyceride levels
HOW DOES CLA WORK?
Most of the properties of CLA involving weight loss actually revolve around weight maintenance; that is the avoidance of weight/ fat gain, rather than fat loss per se. This by no means diminishes it’s relevance in weight loss programs, since 95% of people who do lose weight regain the weight they had lost. If conjugated linoleic acid can prevent this weight gain from occurring, it certainly is a significant tool.
This poses the question of whether it would have to be taken indefinitely. According to Dr. Michael Pariza, who has conducted research on CLA with the University of Wisconsin-Madison:
“CLA doesn’t make a big fat cell get little.
What it rather does is keep a little fat cell from getting big.”
It is hypothesized that conjugated linoleic acid helps glucose pass into muscle cells more effectively, thus preventing glucose from being converted into fat. It is also thought to help fats enter the cell membranes of muscle and connective tissue, where the fat is burned for fuel.
ANY SCIENTIFIC EVIDENCE FOR CLA?
Despite the fact that conjugated linoleic acid was once thought to have great promise in the treatment of obesity, it has so far been unable to produce enough evidence to conclusively prove or disprove its usefulness as a weight loss aid.
Research on CLA weight loss supplements in humans is still very limited. So far, studies on humans have been unable to reproduce the purported weight loss results with as much consistency, as reported in animal studies.
A possible explanation of this inconsistency is that the doses of conjugated linoleic acid generally used in animal studies greatly exceed those used in human studies. This may explain why potential benefits of CLA, other than weight loss, such as anti-cancer and antioxidant properties, improvement of immune function and cardiovascular benefits, have also remained unproven in many human studies.
While fat loss is far more convincing in animal studies than in human studies, some of the human trials have found that conjugated linoleic acid can reduce body fat, are listed below.
- For example, a double-blind, randomized, placebo-controlled study, published in the December 2000 issue of the Journal of Nutrition found that CLA reduced fat and preserved muscle tissue in human volunteers. The study found that approximately 3.4 grams of CLA per day was needed to obtain the beneficial effects of CLA on body fat.3
- Another double-blind, placebo-controlled study published in 2004 in the American Journal of Clinical Nutrition, in which volunteers were given CLA for a period of one year, found that long-term supplementation with CLA reduces body fat in healthy overweight adults. It also concluded that CLA was most effective in those volunteers with a higher Body Mass Index and that those with a higher degree of body fat were more likely to lose fat with CLA supplementation than those with lower a lower body fat percentage. This study was then continued for a further year and results showed that supplementation with CLA for 24 months led to a 6–8% reduction in body fat mass.45
- A randomized, double-blind, placebo-controlled study on overweight human volunteers (BMI 25–30) and were not restricted by a controlled diet, were given 3.2 g per day CLA for 6 months, published in the International Journal of Obesity in 2007, yielded positive results for CLA as a weight loss tool. Those volunteers who were given CLA continued to experience weight loss during the holiday season (November and December), despite reporting decrease physical activity, while the volunteers who were given placebo tablets, experienced weight gain during this time. Thus, CLA supplementation not only significantly reduced body fat over 6 months; it also prevented weight gain during the holiday season. However, this study also concluded “Although no adverse effects were seen, additional studies should evaluate the effect of prolonged use of CLA.”6
However, while some studies have yielded significant fat loss, others have reported negligible changes in body fat.
The Side-Effects of CLA
Safety is the most important issue to consider in your decision of taking a supplement. Currently, the available research leaves unanswered questions as to whether long-term use of CLA supplements by humans is safe. Safety and toxicity levels have not yet established and side effects have not been well documented.
Some CLA studies have reported negative effects. These negative effects have been mainly been reported in animal studies, since these studies use significantly higher doses of CLA than those used in human trials. This suggests that there may be a dose related problem with conjugated linoleic acid.
Increase the dose and the positive properties such as weight loss appear, but the negative effects also take hold. Decrease the dose of conjugated linoleic acid to avoid the negative effects and the benefits of CLA also disappear.
Studies in humans suggest that CLA can trigger insulin resistance (leading to high blood sugar), thus increasing risk of developing diabetes and an increased risk of developing cardiovascular and inflammatory diseases.7
Thus, one should be cautious when using conjugated linoleic acid supplements. Pregnant or lactating women should probably refrain from taking CLA completely.
Some people report feeling nauseous after taking their conjugated linoleic acid, suffering gastrointestinal upset, or loose stools.8
The research shows that CLA only has a modest impact on weight loss, but may have long-term side effects. It is not a magic pill and may not be worth the risk. You will still need to incorporate it into a weight loss program that includes a healthy nutritious reduced calorie diet and regular vigorous exercise, in order to successfully lose weight and keep it off.