What is CLA and Where Does it Come From?
Conjugated Linoleic Acid, or CLA, is a naturally occurring omega-6 fatty acid found in small amounts in meat and dairy products from ruminant animals like cows, goats, and sheep. The highest concentrations are typically found in products from grass-fed animals. CLA is not a single compound but a group of different isomers, with the primary ones being c9,t11 and t10,c12.
CLA supplements, on the other hand, are not derived from these natural dietary sources. They are industrially produced by chemically altering linoleic acid found in vegetable oils, such as safflower oil. This manufacturing process results in a different isomer composition compared to naturally occurring CLA, which is a key factor in its varying effects on the human body.
How CLA Is Theorized to Influence Weight and Body Composition
Early animal studies showed significant reductions in body fat with CLA supplementation, leading to speculation about its potential benefits for humans. The proposed mechanisms behind CLA's effects include:
- Boosting metabolism: CLA is believed to increase the rate at which the body burns calories and fat, potentially by increasing energy expenditure.
- Increasing fat burning: Some research suggests CLA increases fat-burning efficiency, possibly by enhancing the activity of enzymes like carnitine palmitoyl-transferase-1 (CPT-1).
- Inhibiting fat accumulation: CLA may reduce the accumulation of fat in adipocytes (fat cells) by inhibiting enzymes involved in fat storage, such as lipoprotein lipase.
- Promoting lean muscle mass: Evidence from animal studies and some human trials indicates that CLA may help increase or preserve lean body mass, which can further aid in boosting metabolism.
A Closer Look at the Human Evidence
While the theoretical mechanisms are compelling, human clinical trials have produced far less convincing results for CLA supplements. A comprehensive review of the evidence reveals a more complicated picture:
The Modest and Conflicting Findings
Multiple meta-analyses of randomized controlled trials have concluded that CLA supplementation in humans produces, at best, modest fat loss. The effects are often statistically significant but clinically minor, and benefits typically plateau after about six to twelve months. Many studies report little to no significant change in overall body weight or BMI.
Where Does the Fat Loss Occur?
Notably, the limited fat loss observed with supplemental CLA appears to primarily affect subcutaneous fat (fat just under the skin), rather than the more harmful visceral fat that surrounds internal organs. This distinction is critical because visceral fat is more closely linked to metabolic and cardiovascular health risks. The potential to reduce only subcutaneous fat makes CLA a less-than-ideal tool for improving overall metabolic health.
Potential Adverse Effects
Research indicates that high intake of supplemental CLA, particularly from products containing a higher proportion of the t10,c12 isomer, may lead to adverse health effects. These include:
- Increased liver fat: Some studies have observed an accumulation of fat in the liver with supplemental CLA intake, potentially contributing to metabolic syndrome.
- Insulin resistance: A significant concern, especially for those at risk of type 2 diabetes, is that CLA supplementation might impair insulin sensitivity.
- Increased inflammation: Markers of inflammation, such as C-reactive protein, have been shown to increase with certain CLA isomers.
- Gastrointestinal issues: Mild side effects like nausea, diarrhea, and stomachaches are relatively common.
CLA in Supplements vs. Natural Food Sources
| Feature | CLA Supplements | Natural Dietary CLA |
|---|---|---|
| Source | Chemically altered linoleic acid from vegetable oils (e.g., safflower oil). | From meat and dairy of ruminant animals (especially grass-fed). |
| Isomer Composition | Often a mix with a high percentage of the t10,c12 isomer, which is less prevalent in food. | Predominantly the c9,t11 isomer, with smaller amounts of others. |
| Concentration | Much higher than natural dietary intake, reflecting amounts used in research. | Much lower, with typical intakes around 150-200 mg per day. |
| Associated Risks | Linked to potential adverse metabolic effects at higher concentrations, including insulin resistance, inflammation, and liver issues. | Not associated with the same negative side effects as higher supplemental concentrations. |
| Safety Profile | Caution recommended, especially for long-term intake at higher concentrations. | Generally regarded as safe and part of a healthy diet. |
The Verdict: Exercise, Diet, and Natural Sources Reign Supreme
While some studies do report marginal positive effects on body composition, the evidence for CLA supplements as a powerful weight loss aid is weak and inconsistent. The potential risks associated with higher supplemental concentrations, particularly concerning insulin sensitivity and liver health, should not be ignored. Instead of seeking a quick fix, health professionals overwhelmingly agree that a balanced diet and regular exercise are the most effective and safest strategies for weight management. For those interested in CLA, obtaining it through natural food sources like grass-fed beef and dairy provides potential benefits without the associated risks of supplements. When considering supplements, always consult a healthcare provider, especially if you have pre-existing health conditions or take other medications.
Further reading: A review on effects of conjugated linoleic fatty acid (CLA) upon body composition and energetic metabolism
Conclusion: Modest Effects, Real Concerns
In conclusion, CLA supplements have not lived up to their early promise as a major fat-burning aid in humans. The reported effects are minimal and inconsistent, far from the dramatic results observed in animal models. The contrasting isomer composition and higher concentrations in supplements, compared to natural sources, introduce potential health risks that outweigh the marginal benefits for many people. For sustainable, healthy weight management, proven strategies involving dietary changes and physical activity remain the gold standard.
