What is Conjugated Linoleic Acid (CLA)?
Conjugated linoleic acid (CLA) is a family of omega-6 fatty acids naturally found in the meat and dairy products of ruminant animals like cows and sheep. The CLA in supplements, however, is synthetically produced by chemically altering linoleic acid from vegetable oils such as safflower oil, resulting in a different isomer profile than naturally occurring CLA. The two main isomers, cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12), are believed to be responsible for most of the supplement’s physiological effects. Understanding this difference is crucial when evaluating the scientific literature, as supplemental use is much higher than dietary intake and may have distinct impacts on the body.
Potential Effects on Body Composition
One of the most widely researched areas for CLA is its effect on body composition, particularly its potential to reduce body fat while preserving lean muscle mass. While animal studies have shown significant fat reduction, results in human trials have been more modest and inconsistent.
The Role in Fat Loss
Studies suggest that CLA influences fat metabolism through several mechanisms:
- Increasing Energy Expenditure: CLA may increase the body's metabolic rate and fat-burning processes.
- Inhibiting Lipoprotein Lipase: This enzyme is responsible for storing fat in adipocytes (fat cells). By inhibiting it, CLA may divert fatty acids to muscle cells to be burned as fuel.
- Triggering Fat Cell Death: Some research suggests CLA, particularly the t10,c12 isomer, may increase apoptosis (programmed cell death) in fat cells.
Preserving Lean Muscle Mass
During periods of calorie restriction for fat loss, there is often a risk of losing muscle mass as well. Some human studies indicate that CLA can help preserve metabolically active lean muscle mass, which is beneficial for maintaining a higher basal metabolic rate. This muscle-sparing effect is particularly valuable for athletes and bodybuilders who want to achieve a more toned physique.
Benefits Beyond Body Composition
While fat loss and muscle preservation are primary reasons for using CLA, some research points to other health benefits. It is important to note, however, that evidence for many of these benefits is still developing or based largely on animal studies.
Immune System Support
CLA may possess immunomodulatory and anti-inflammatory properties. It is thought to influence critical pathways of immune cell differentiation and potentially reduce the production of pro-inflammatory cytokines. This could be beneficial for overall immune system function, though research results on its effect on inflammation and oxidative stress in humans are mixed.
Heart Health and Metabolism
Some studies, particularly observational ones, have linked higher dietary intake of natural CLA to improved heart health indicators. Research has also explored its potential role in managing blood lipid profiles by decreasing LDL cholesterol. However, other studies have shown potential negative impacts on metabolic parameters, including increased triglycerides and insulin resistance, especially with supplemental use.
Bone Health and Other Areas
- Bone Mineralization: Some evidence suggests CLA may positively influence calcium and bone metabolism, leading to improved bone strength.
- Physical Performance: Certain studies have shown that CLA, often in combination with exercise, can lead to modest improvements in physical performance, potentially by supporting fat oxidation during workouts.
Comparison: CLA vs. Placebo
| Feature | CLA Supplement | Placebo (e.g., Safflower Oil) |
|---|---|---|
| Effect on Fat Mass | Modest reduction, typically over 6+ months. | Negligible change or small gain. |
| Effect on Lean Mass | Potential for preservation or modest increase, particularly in those with higher physical activity. | Typically unchanged, or may decrease during calorie deficit. |
| Insulin Sensitivity | Mixed results; some studies show potential for worsening insulin resistance with high doses. | No specific impact. |
| Side Effects | Potential for mild GI issues (nausea, diarrhea), headaches, fatigue. | Typically none, unless allergic to oil base. |
| Optimal Use | Combined with consistent diet and exercise over a long period. | Dependent on the individual's diet and lifestyle. |
| Cost | Regular ongoing cost for supplementation. | No additional cost. |
Potential Risks and Considerations
Despite the documented benefits, it is crucial to approach CLA supplementation with a balanced perspective. Many of the impressive results seen in animal studies have not been replicated in humans, where effects are generally much smaller. Furthermore, potential side effects and long-term health concerns exist, especially with high supplemental use:
- Gastrointestinal Issues: Mild to moderate side effects like nausea, diarrhea, and stomach upset are commonly reported.
- Insulin Resistance: Some human studies have shown that high supplemental use of CLA, particularly certain isomers, can increase insulin resistance and negatively affect glucose metabolism.
- Lipid Profile Alterations: CLA has been reported to cause negative changes in blood lipids, including increased triglycerides and LDL cholesterol, and a decrease in beneficial HDL cholesterol.
- Fatty Liver: Animal and some human studies suggest that high use of supplemental CLA can cause fat to accumulate in the liver.
These risks highlight the importance of consulting a healthcare professional before starting any new supplement regimen, especially if you have pre-existing conditions like diabetes or metabolic syndrome.
Conclusion
Conjugated linoleic acid supplements have been shown in human meta-analyses to offer a modest reduction in body fat over the long term, and may also help preserve lean muscle mass, especially when combined with a healthy diet and regular exercise. Other potential benefits, including immune modulation and bone health, have been explored, though evidence is less conclusive and often based on animal or early human research. However, it's vital to acknowledge the mixed and sometimes contradictory findings in human trials, as well as the potential for side effects with supplemental use. Since the CLA found in supplements is different from natural dietary sources and is taken in much higher amounts, its long-term effects warrant careful consideration. Ultimately, while CLA can be a supportive tool, it is not a magic bullet and should be viewed as part of a holistic wellness plan rather than a standalone solution for significant weight or body composition changes. Learn more about the differences between natural and supplemental CLA here.
