What is the CLA supplement good for?

Conjugated Linoleic Acids (CLA)

Importance for the reduction of body fat in case of obesity

Question: Can overweight patients be helped to reduce their body fat by supplementing certain fatty acids?

Answer: There is insufficient evidence that CLA supplementation is effective. Side effects cannot be ruled out.

The conjugated linoleic acids (CLA, conjugated linoleic acids) are said to have the effect of reducing body fat, primarily based on the results of animal experiments. Although there is a lack of meaningful research results on humans, numerous Internet providers and drugstores are already marketing CLA supplements or products containing CLA as slimming aids for overweight people or as muscle building substances for athletes. The increasing popularity of CLA as a dietary supplement requires scientifically based education of the population about its use in humans: How should the postulated effect of CLA be assessed? Is CLA supplementation safe and harmless to health?

What are conjugated linoleic acids?

Conjugated linoleic acids (conjugated octadecadienoic acids, CLA) represent a group of polyunsaturated fatty acids that are isomers of linoleic acid (cis-9, cis-12-octadecadienoic acid) (Fig. 1). The greatest biological activity is attributed to the isomers in the cis-9, trans-11 and the trans-10, cis-12 configuration.

Fig. 1: conjugated linoleic acid

Where do conjugated linoleic acids occur?

CLA are formed as a metabolic product of linoleic acid in the rumen of ruminants by the linoleic acid isomerase of the pancreatic bacterium Butyrivibrio fibrisolvens. CLA is also formed in the tissues of ruminants (e.g. mammary glands), here through the desaturation of trans-11-octadecenoic acid (trans-vaccenoic acid).

Thus ruminant meat (beef, lamb) as well as milk and dairy products are the main sources of CLA in human nutrition. Over 90% of the CLA ingested through food consist of the cis-9, trans-11 isomer. Commercial CLA supplements, on the other hand, usually contain mixtures of different CLA isomers with a high content of the cis-10, trans-12 isomer.

In humans, CLA can also be formed by isomerization from linoleic acid, induced by anaerobic microbial activities in the intestine or by free radicals. Furthermore, they can also be produced by desaturation from trans-vaccenic acid. Certain tissues in the human body therefore contain small amounts of CLA.

How do conjugated linoleic acids affect body composition?

In animal experiments, CLA supplementation causes v. a. in mice, a decrease in body fat content and an increase in muscle mass. However, the randomized, placebo-controlled clinical studies on humans carried out on this question do not provide this clear result. As shown in various reviews and also derived from individual current clinical studies, the results obtained so far in humans do not yet give a uniform picture.

The effects of CLA on body fat content in humans are much weaker than in mice. When looking at the CLA doses used in the respective studies as the amount in relation to the energy intake (g / MJ / day), this initially seems surprising, because these were in some cases comparable: a dosage of 1.4 to 6.8 g / day in humans (approx. 0.14-0.68 g / MJ of metabolizable energy) the body fat content is reduced by approx. 2 to 6%, in one study even by 22%. Feeding a diet enriched with 1% CLA (approx. 0.5 g CLA / MJ) leads to a body fat decrease of 60% in mice. One possible reason for this could be that the mice used as experimental animals have a higher metabolic rate than humans. However, different measurement methods (direct measurement of body composition in dissected animals and bioimpedance or DXA in humans) could also play a role in these findings. However, if the amount of CLA is not considered in relation to energy intake, but in relation to body weight (mg / kg / day), the weaker effects observed in humans can be more clearly explained: In the human studies, 25 to 80 mg CLA per kg Body weight and day used - this is only about one-fiftieth of the dose used in studies with mice. This is probably one of the reasons for the inadequate transferability of the findings obtained in animal experiments to humans.

The CLA isomer with the body fat lowering effect is the trans-10, cis-12 isomer. In animal experiments, the effect of the trans-10, cis-12 isomer appears to be dependent on the dose and duration of the supplementation as well as the species, age and sex. It should be emphasized that all animal experiments were carried out on young, growing animals; the effect of CLA on body composition in adult animals is not known. In contrast, the results in humans do not provide any indication of a dose-effect relationship.

The mechanism of a possible reduction in body fat content through CLA is v. a. Based on the results of animal experiments, factors such as the increase in fat oxidation, the activation of the fat transport systems (carnitine palmitoyl transferase activity) and the inhibition of lipoprotein lipase activity in the adipocytes (reduction in triglyceride uptake and storage) are postulated.

Some of the studies in humans, as well as the experiments in mice, suggest that the body fat-lowering effect of CLA is associated with an increase in lean body mass. Here, too, the mechanism has not been clearly clarified and the results so far are inconsistent. In a human study on the effect of CLA on weight progression after weight loss, CLA did not reduce weight gain, but the increase in body fat was reduced compared to the placebo group. It was consequently shown in this study that CLA supplementation leads to an increase in lean body mass, regardless of the percentage weight gain and regardless of physical activity. In this way, CLA can indirectly increase the resting energy expenditure as a result of the increased lean body mass. This provides an explanation for the increased energy consumption by CLA observed in some studies.

Why is the informative value of previous human studies limited?

Most of the studies were carried out on people in their normal everyday life, so that different nutrient and energy intake and consumption may have occurred. This, of course, can interfere with the relatively small effects of CLA on body composition. Additionally, compliance in the human studies ranged from 77-100%, and these differences in compliance can affect results. The same goes for the way in which CLA is administered: in most studies, CLA is administered as free fatty acids in the form of a supplement, but there are also studies in which they are given in the form of triglycerides as a supplement or in fortified butter. Many of the studies on CLA supplementation were only conducted in a small study population and only over a short period of time (1 to 2 months). The long-term effect on fat mass and body weight remains open. To date, there have been few human studies of the mechanism of CLA's action and the results are inconsistent.

Are there any side effects?

Studies in mice show that the trans-10, cis-12-CLA isomer can cause undesirable effects such as insulin resistance, increased plasma insulin concentrations, hyperlipidemia and decreased plasma leptin concentrations. There is evidence that some of these effects can also manifest in humans. Studies with male volunteers also exist in which increased lipid peroxidation was observed as a result of CLA supplementation, which indicates a potential adverse effect on the cardiovascular system.


There is insufficient evidence that CLA supplementation is effective in reducing body fat and weight loss. Side effects of CLA supplementation cannot be ruled out. Before conclusions can be drawn and recommendations can be made, further studies in humans that are controlled for nutrient and energy intake are necessary, in which pure CLA isomers are used to clearly determine short and long-term effects as well as undesirable side effects of each individual CLA isomer .


  1. Belury, Mahon, Banni: The Conjugated Linoleic Acid (CLA) Isomer, t10c12-CLA, Is Inversely Associated with Changes in Body Weight and Serum Leptin in Subjects with Type 2 Diabetes Mellitus. J Nutr 133 (2003) 257S-260S
  2. Desroches, Chouinard, Galibois et al .: Lack of effect of dietary conjugated linoleic acids naturally incorporated into butter on the lipid profile and body composition of overweight and obese men. Am J Clin Nutr 82 (2005) 309-319
  3. European Food Safety Authority (EFSA): Opinion of the Scientific Panel on Dietetic Products, Nutrition and Allergies on a request from the Commission related to the presence of trans fatty acids in foods and the effect on human health of the consumption of trans fatty acids. The EFSA Journal 81 (2004) 1-49; www.efsa.eu.int/science/nda/nda_opinions/588/opinion_nda09_ej81_tfa_en1.pdf
  4. Gaullier, Halse, Høye et al .: Supplementation with Conjugated Linoleic Acid for 24 Months Is Well Tolerated by and Reduces Body Fat Mass in Healthy, Overweight Humans. J Nutr 135 (2005) 778-784 (abstract)
  5. Gaullier, Halse, Høye et al .: Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans. Am J Clin Nutr 79 (2004) 1118-1125
  6. Haugen, Alexander: Can linoleic acids in conjugated CLA products reduce overweight problems? Tidsskr Nor Laegeforen 124 (2004) 3051-3054 (abstract)
  7. Jeukendrup, Aldred: Fat supplementation, health, and endurance performance. Nutrition 20 (2004) 678-688 (abstract)
  8. Kamphuis, Lejeune, Saris, Westerterp-Plantinga: The effect of conjugated linoleic acid supplementation after weight loss on body weight regain, body composition, and resting metabolic rate in overweight subjects. Int J Obes Relat Metab Disord 27 (2003) 840-847
  9. Kraft, Jahreis: Conjugated Linoleic Acids: Genesis and Metabolic Effects. Nutrition Umschau 48 (2001) 348-354
  10. Larsen, Toubro, Astrup: Efficacy and safety of dietary supplements containing CLA for the treatment of obesity: evidence from animal and human studies. J Lipid Res 44 (2003) 2234-2241
  11. Pariza: Perspective on the safety and effectiveness of conjugated linoleic acid. Am J Clin Nutr 79 (2004) 1132S-1136S
  12. Rainer, Heiss: Conjugated linoleic acid: health implications and effects on body composition. J Am Diet Assoc 104 (2004) 963-968 (abstract)
  13. Risérius, Vessby, Ärnlöv, Basu: Effects of cis-9, trans-11 conjugated linoleic acid supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men. Am J Clin Nutr 80 (2004) 279-83
  14. Risérius, Vessby, Arner, Zethelius: Supplementation with trans10cis12-conjugated linoleic acid induces hyperproinsulinaemia in obese men: close association with impaired insulin sensitivity. Diabetologia 47 (2004) 1016-1019
  15. Terpstra: Effect of conjugated linoleic acid on body composition and plasma lipids in humans: an overview of the literature. Am J Clin Nutr 79 (2004) 352-261
  16. Wang, Jones: Dietary conjugated linoleic acid and body composition. Am J Clin Nutr 79 (2004) 1153S-1158S

German Nutrition Society: Conjugated Linoleic Acids (CLA). DGEinfo (02/2006) 23-25