What is Conjugated Linoleic Acid?
Conjugated linoleic acid, or CLA, is a naturally occurring fatty acid found primarily in the meat and dairy products of ruminant animals like cows and sheep. In its natural, food-based form, the cis-9, trans-11 isomer is the most prevalent. As a dietary supplement, CLA is typically produced by chemically altering linoleic acid from vegetable oils, creating a mixture of different isomers, often a 50:50 blend of the cis-9, trans-11 and trans-10, cis-12 isomers. Supplemental doses are significantly higher than the amounts obtained from diet alone, which is a critical factor when considering potential health impacts.
The Research on CLA and Kidney Function in Humans
For healthy individuals, the current body of human research offers reassurance regarding CLA's impact on kidney health. The U.S. Food and Drug Administration (FDA) has granted CLA a "Generally Recognized as Safe" (GRAS) status, and multiple human studies have found no serious adverse effects at typical daily doses, which range from 3.2 to 6.4 grams.
A 2010 study published in Food and Chemical Toxicology provided particularly strong evidence. In this trial, 20 healthy subjects consumed a very high dose of CLA (19.3 grams/day) for three weeks. Researchers measured markers of both liver and kidney function throughout the study. The results showed no clinically significant changes in kidney function, with all mean values for the tested markers remaining within the normal range.
Considerations for Individuals with Pre-existing Kidney Conditions
While the data is promising for healthy people, individuals with existing kidney disease should proceed with caution. The safety and efficacy of CLA supplementation have not been well established for people with chronic or severe kidney disease. For these populations, the body's slower removal of substances could increase the risk of side effects, so CLA supplementation should only be considered under the supervision of a physician.
Insights from Animal Studies
The relationship between CLA and kidney function appears more complex in animal studies, which have yielded mixed results. It is important to note that findings in animal models, particularly at very high doses, do not always translate directly to human responses.
- Potential for Benefit: Some animal studies suggest CLA may have protective effects. For instance, research on rats with a model of polycystic kidney disease (PKD) showed that CLA supplementation reduced inflammation, fibrosis, and the release of pro-inflammatory markers in the kidneys. Another study on rats found that CLA pretreatment reduced renal damage caused by ischemia/reperfusion injury.
- Potential for Toxicity: On the other hand, another study on a different rat model of kidney disease showed potential functional toxicity at high doses in female animals, with a significant increase in serum creatinine. The researchers noted that these effects were dose-dependent and warranted further exploration. This highlights the importance of dose and individual factors, which may include gender.
Isomer Differences and Their Effects
The different isomers of CLA are a key area of research, as their effects on the body can vary significantly. CLA supplements typically contain a mixture of isomers, predominantly cis-9, trans-11 and trans-10, cis-12, but their individual impacts differ:
- cis-9, trans-11 (rumenic acid): This is the predominant isomer found naturally in food sources like dairy and beef. It is often associated with the general health benefits observed in epidemiological studies, and some research suggests it may possess anti-inflammatory properties.
- trans-10, cis-12: This isomer is largely responsible for the anti-obesity effects seen in animal models and some human studies. However, at higher supplemental doses, this specific isomer has been linked to potential adverse metabolic effects, including increased inflammation, insulin resistance, and negative changes in lipid profiles. This differential effect underscores why the balance of isomers and the dosage are so important.
Comparative Impact on Renal Markers: CLA vs. Placebo
The following table compares the findings from a placebo-controlled human study regarding the effect of high-dose CLA on key renal and metabolic markers.
| Marker Measured | Healthy Subjects (19.3g CLA/day, 3 weeks) | Placebo Group (Comparison) | Conclusion |
|---|---|---|---|
| Serum Creatinine | Values remained within the normal range. | Also within the normal range. | No clinically relevant effect on kidney function observed with high-dose CLA. |
| Serum Urea | Values remained within the normal range. | Also within the normal range. | High CLA intake did not alter this marker of kidney function. |
| Liver Enzymes (e.g., GGT) | Minor, non-clinically significant elevation. | No significant changes. | While a minor change was noted, it was not considered clinically relevant. |
Conclusion: Weighing the Evidence on CLA and Kidney Safety
Based on current research, especially in controlled human studies, CLA supplementation does not appear to cause kidney problems in healthy individuals when taken at typical, recommended dosages (up to 6 grams per day). High-intake, short-term human trials have confirmed this finding, showing no clinically relevant changes to kidney function markers. However, the picture is more nuanced when considering specific isomers, dosage levels, and individual health status. Animal studies, particularly those involving very high doses or specific disease models, have presented conflicting results, with some pointing to potential toxicity risks.
For those with existing kidney conditions, supplement use carries a higher degree of uncertainty, and medical consultation is essential before considering CLA. Furthermore, the synthetic nature of most supplements, with its higher concentration of isomers like trans-10, cis-12, differentiates it from the CLA found naturally in food. Therefore, while healthy individuals can likely use CLA with minimal risk to their kidneys, caution is advised for specific populations, and more long-term human research is needed to fully understand all potential effects.
Potential Side Effects Beyond Kidney Function
Beyond the specific concern about kidney health, CLA has been associated with other side effects, particularly when taken in high doses. These include common gastrointestinal issues such as stomach upset, diarrhea, and nausea. Certain isomers, notably trans-10, cis-12 at higher intake levels, have been linked to increased inflammation, insulin resistance, and potential negative impacts on lipid profiles like HDL cholesterol. This complexity highlights the need for careful consideration and professional guidance before beginning any new supplement regimen.
Learn more about conjugated linoleic acid and metabolic health on PubMed.
