What Exactly is Conjugated Linoleic Acid (CLA)?
Conjugated linoleic acid, or CLA, is a type of omega-6 polyunsaturated fatty acid. Unlike the industrial trans fats widely known to be harmful, CLA is a naturally occurring trans fat found in the meat and milk of ruminant animals like cows, goats, and sheep. The CLA available in most dietary supplements, however, is not derived from these natural sources. Instead, it is produced by chemically altering linoleic acid from vegetable oils, typically safflower oil.
The isomers of CLA
CLA is a family of different isomers, or variations, of linoleic acid. The two major types relevant to nutrition are cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12). The natural CLA in grass-fed animal products is predominantly the c9,t11 isomer, which appears to have anti-inflammatory effects. In contrast, supplemental CLA is often sold as a 50:50 mixture of c9,t11 and t10,c12, and it is the t10,c12 isomer that has been linked to potential fat loss.
The Proposed Mechanisms and Modest Human Results
Initial interest in CLA was driven by promising animal studies showing significant fat reduction and other health benefits. Researchers theorized CLA works in several ways, including increasing fat burning (fat oxidation), inhibiting the production of new fat cells (adipogenesis), and stimulating fat breakdown (lipolysis). However, human studies have largely failed to replicate the dramatic effects seen in animals, and results are frequently inconsistent.
Weight loss and fat metabolism
For those seeking fat loss, CLA's point is its potential to modestly reduce body fat, especially in the first few months of supplementation. A meta-analysis of human trials found CLA produced a small, but statistically significant, reduction in body fat over time. However, this effect is often insignificant in a real-world context, with one review noting an average loss of only 0.2 pounds per week over six months. Some studies report no effect at all.
Preserving lean muscle mass
An interesting aspect of CLA for fitness enthusiasts is its potential to help preserve lean muscle mass during weight loss. This can help maintain a higher metabolic rate, which is crucial for long-term weight management. Some studies suggest a greater increase in muscle mass in subjects performing resistance training while taking CLA.
Immune system modulation
Early animal research suggested CLA could have immunomodulatory effects, reducing inflammation and potentially aiding in immune responses. In human trials, however, the immune benefits are less clear and have shown minimal, if any, significant effects.
Potential Risks and Side Effects of CLA Supplements
Despite being considered 'Generally Recognized as Safe' (GRAS) by the FDA for certain applications, high supplemental doses of CLA are associated with several risks, especially when taken long-term. This is a major factor to consider for anyone assessing the point of CLA.
- Gastrointestinal Issues: Mild to moderate side effects like upset stomach, nausea, diarrhea, and bloating are commonly reported.
- Metabolic Concerns: Large doses of supplemental CLA have been shown to increase fat accumulation in the liver, potentially leading to insulin resistance and other metabolic issues, particularly with the t10,c12 isomer.
- Altered Cholesterol Levels: Some human studies have reported that supplemental CLA can lower 'good' HDL cholesterol, raising concerns about its effect on heart health.
- Bleeding Risk: CLA may slow blood clotting, which can be a risk for people with bleeding disorders or those taking anticoagulant medications.
Comparison Table: Natural CLA vs. Supplemental CLA
| Feature | Natural CLA (Food) | Supplemental CLA (Capsules) |
|---|---|---|
| Source | Produced naturally by ruminant animals like cows and sheep. | Chemically altered from linoleic acid in vegetable oils, like safflower. |
| Isomer Ratio | Primarily the c9,t11 isomer, associated with anti-inflammatory effects. | Usually a 50:50 mix of c9,t11 and t10,c12 isomers. |
| Dosage | Low, consumed as part of a regular diet. | High, typically 3-6 grams per day. |
| Side Effects | Generally considered safe, no adverse effects reported from dietary levels. | Mild GI issues, risk of insulin resistance and fatty liver at high doses. |
| Efficacy | Linked to improved metabolic health in observational studies. | Inconsistent, modest effects on fat loss in humans. |
Conclusion: Is There a Point to CLA Supplements?
For many, the point of CLA supplementation remains questionable. While animal studies and marketing claims often promise significant benefits for fat loss and muscle building, the evidence in humans is far more modest and conflicting. The potential fat loss from supplements is small in the grand scheme of overall health, and this marginal effect must be weighed against the potential risks and side effects, including metabolic issues and altered cholesterol levels. The natural CLA found in grass-fed meat and dairy, however, seems to be a more beneficial source, associated with better metabolic health outcomes in observational studies without the risks of high, synthetic doses. For those seriously pursuing fitness goals, focusing on proven strategies like a balanced diet, regular exercise, and adequate protein intake is a more effective and safer path than relying solely on CLA supplementation. A healthcare professional should be consulted before starting any new supplement regimen, especially for individuals with underlying health conditions or those on medication. A balanced lifestyle is often more potent than any single supplement. For more in-depth nutritional guidance, consider visiting authoritative sources like Healthline [https://www.healthline.com/nutrition/conjugated-linoleic-acid].
Is CLA the Right Supplement for You?
Considering the limited, inconsistent evidence for significant human benefits and the potential for side effects, the point of CLA as a standalone supplement for most people is debatable. Natural CLA from food sources is likely the healthier and safer option. Anyone considering supplementation should first consult a healthcare provider and recognize that its effects are far from guaranteed and will be modest at best.
What are the main benefits of taking CLA?
- Modest Fat Loss: Some human trials show a small reduction in body fat, particularly within the first six months of supplementation.
- Muscle Preservation: It may help preserve lean muscle mass during periods of weight loss or calorie restriction.
- Immune System Support: Some animal and limited human studies suggest potential for immune system modulation, though effects are inconsistent.
What are the main risks of taking CLA?
- Inconsistent Results: Human studies often show no significant effect on weight or body fat, unlike the more promising animal studies.
- Adverse Metabolic Effects: High doses of supplemental CLA may lead to insulin resistance, increased liver fat, and changes in cholesterol levels.
- Gastrointestinal Distress: Common mild side effects include nausea, diarrhea, and stomach upset.
- Interaction with Medications: CLA can interfere with blood clotting and may interact with medications for high blood pressure or blood thinners.
