What is Conjugated Linoleic Acid (CLA)?
Conjugated linoleic acid, or CLA, is a group of geometric and positional isomers of linoleic acid, a type of polyunsaturated omega-6 fatty acid. While linoleic acid has a specific double-bond arrangement, CLA's structure is altered, with two double bonds that are "conjugated," or adjacent to one another. There are 28 known isomers of CLA, but the two most studied and biologically active are cis-9, trans-11 (c9, t11) and trans-10, cis-12 (t10, c12).
Naturally, CLA is formed in the digestive system of ruminant animals like cows, goats, and sheep. This means it is present in their meat and dairy products, with grass-fed animals tending to have higher levels. For supplementation, CLA is often produced by chemically altering linoleic acid from vegetable oils, such as safflower oil.
The Mechanisms Behind CLA's Action
The beneficial effects of CLA are linked to its ability to influence several key metabolic and signaling pathways within the body. At a molecular level, CLA is known to interact with nuclear receptors called peroxisome proliferator-activated receptors (PPARs). These receptors play a crucial role in regulating fatty acid metabolism, energy balance, and inflammatory responses.
Affecting Fat Metabolism and Body Composition
CLA's most researched benefit is its impact on body composition, particularly its ability to influence body fat and lean muscle mass. It accomplishes this through multiple mechanisms:
- Increasing Lipolysis: CLA can significantly increase the rate of lipolysis, which is the breakdown of fat into fatty acids. Studies suggest the t10, c12 isomer is particularly potent in this regard within human adipocytes (fat cells).
- Reducing Lipogenesis: It also works to decrease lipogenesis, the process of synthesizing and storing fat. The t10, c12 isomer can inhibit the activity of the enzyme lipoprotein lipase (LPL), which is crucial for fat storage in adipocytes.
- Inhibiting Adipocyte Differentiation: Research indicates that CLA can help control the expression of genes involved in the differentiation of pre-adipocytes into mature fat cells.
- Enhancing Fatty Acid Oxidation: CLA can increase the activity of carnitine palmitoyl-transferase-1 (CPT-1), an enzyme that helps transport fatty acids into the mitochondria for oxidation (burning).
Supporting the Immune System
CLA has demonstrated immunomodulatory effects, meaning it can regulate or adjust the body's immune function. Research points to several ways it supports immune health:
- Anti-Inflammatory Action: CLA may possess anti-inflammatory properties, with some studies showing it can help reduce the production of pro-inflammatory cytokines like TNF-α and IL-1β. The c9, t11 isomer appears to be more prominent in these anti-inflammatory effects.
- Modulating Cytokines: It can affect the balance of immune-related signaling molecules (cytokines). For example, some studies found CLA supplementation decreased pro-inflammatory markers while increasing anti-inflammatory ones.
- Altering Immune Cell Characteristics: CLA can change the fatty acid profile of cell membranes in immune cells, which can influence their function and signaling capabilities.
Other Health Benefits and Considerations
Beyond its effects on body composition and the immune system, CLA has been studied for other potential health benefits, though research results are often mixed or less conclusive in humans compared to animal models.
Effects on Metabolic Health and Cardiovascular Risk
Some research suggests CLA could improve insulin sensitivity, but this is complicated. In many human trials, particularly with specific isomers (t10, c12), negative effects on glucose metabolism and lipid profiles have been observed. These potential negative effects include increased insulin resistance and altered cholesterol levels. However, other studies have shown potential benefits, such as reducing blood pressure when combined with certain medications. This highlights the need for careful consideration and professional advice.
Role in Bone Health
Animal studies have indicated that CLA might benefit bone formation and inhibit bone resorption. However, human clinical trials have produced inconsistent results and more research is needed to determine any real effect on markers of bone health.
Comparison of CLA Isomers
The two most prominent isomers of CLA, c9, t11 and t10, c12, can have distinct and sometimes opposing effects on the body. This is why the precise composition of a CLA supplement can be important for its physiological impact.
| Feature | cis-9, trans-11 (c9, t11) Isomer | trans-10, cis-12 (t10, c12) Isomer |
|---|---|---|
| Primary Source | Predominant isomer found in natural food sources like grass-fed dairy and beef. | Less prevalent in natural sources; a key component of synthetic supplements. |
| Anti-Inflammatory | Considered to be primarily responsible for CLA's anti-inflammatory properties. | Can sometimes increase inflammatory markers. |
| Body Fat Reduction | Has a modest effect on fat reduction. | Considered the main anti-adiposity isomer, increasing lipolysis and inhibiting fat cell differentiation. |
| Lean Mass | Positive effects may involve anabolic processes, supporting lean muscle mass. | More linked to catabolic processes and fat oxidation. |
| Metabolic Impact | Some studies suggest better tolerance concerning insulin sensitivity. | Linked to potential negative effects like increased insulin resistance. |
The Safety and Source of CLA
While CLA occurs naturally in food, supplementation provides much higher dosages than typically consumed in a diet. A standard dietary intake is estimated to be relatively low compared to the amounts often used in supplements. Natural intake from food is generally considered safe, but the effects of high-dose supplementation require more caution. The FDA has granted CLA a "Generally Recognized as Safe" (GRAS) status for food addition, but potential adverse effects with supplementation, such as gastrointestinal upset, fatigue, and negative metabolic changes, particularly at higher concentrations, have been reported. Given the mixed results and potential risks associated with high supplemental amounts, consulting a healthcare provider before starting a CLA supplement is highly recommended.
Conclusion
CLA helps the body primarily by influencing fat metabolism and modulating the immune system, with distinct roles played by its different isomers. Its capacity to reduce body fat, increase lean mass, and provide anti-inflammatory support is well-established in animal models and some human studies. However, the evidence from human trials is often inconsistent, and potential side effects, especially with high supplemental amounts of specific isomers, warrant caution. The most reliable and safest way to obtain CLA is through a diet rich in naturally occurring sources like meat and dairy from grass-fed animals. For those considering supplementation, it is important to be aware of the mixed research findings and potential risks. In summary, while CLA offers promising health benefits, it should be approached with a balanced perspective, prioritizing dietary sources and professional advice over high-dose supplements.
[1] How Does CLA Help the Body? Benefits on Fat, Immunity & More | Healthline. https://www.healthline.com/nutrition/conjugated-linoleic-acid
