What Does CLA Do for My Body? Exploring Fat Loss, Muscle, and Health

November 15, 2025 •

4 min read

According to a review of 18 human trials, conjugated linoleic acid (CLA) was found to cause only modest fat loss over six months, despite popular claims of its effectiveness for weight management. This fatty acid is naturally found in meat and dairy but often consumed as a supplement for its purported body composition benefits.

Quick Summary

Conjugated linoleic acid (CLA) is a fatty acid studied for its effects on body composition, including modest fat loss and muscle retention. Research shows varying results and potential side effects, especially with supplements, compared to CLA found naturally in food.

Key Points

Modest Fat Loss: CLA has been shown in some human studies to cause a small, modest reduction in body fat mass, particularly during the first six months of supplementation.
Muscle Preservation: Some evidence suggests CLA can help preserve lean muscle mass, especially when combined with a regular exercise routine.
Natural vs. Supplemental CLA: The CLA found in food (mostly from grass-fed ruminants) differs chemically from the synthetic CLA in supplements, which can contain higher, potentially harmful amounts.
Potential Risks: High amounts of supplemental CLA have been associated with side effects including gastrointestinal issues, increased inflammation, and a risk of insulin resistance.
Mixed Scientific Evidence: Research on CLA's benefits for weight loss, muscle growth, and other health markers is inconsistent in humans, despite promising results in animal studies.
Not a Weight-Loss Solution: Relying solely on CLA supplements for significant weight or fat loss is generally not effective, and a balanced diet and exercise are safer and more reliable methods.

Understanding Conjugated Linoleic Acid (CLA)

Conjugated linoleic acid (CLA) is a group of isomers of the omega-6 fatty acid, linoleic acid. It was discovered in the 1980s and is primarily found in meat and dairy from ruminant animals. Key isomers include cis-9, trans-11 (c9, t11), prevalent in food, and trans-10, cis-12 (t10, c12), often found in higher amounts in supplements. Naturally occurring CLA differs from industrial trans fats and is found in healthy foods, but supplemental CLA, produced by chemically altering vegetable oils, has a different isomer balance and potential effects.

What Science Says: CLA's Effects on Body Composition

Early animal studies showed significant reductions in body fat with CLA, but human studies have yielded more modest and inconsistent results. Research focuses mainly on fat loss and muscle preservation.

Fat Loss: Modest but Inconsistent Results

Human studies on CLA's impact on fat loss show mixed findings. Some analyses indicate a small reduction in body fat mass, particularly over the initial six months of supplementation. However, many studies, especially long-term ones, report no significant effect on body weight or fat. The proposed mechanism involves reducing fat storage and increasing fat burning.

Muscle Mass: Lean Body Preservation

CLA has also been studied for its effect on lean body mass.

Some research suggests CLA might help preserve muscle mass, which is beneficial during calorie restriction.
This effect is appealing for individuals aiming for a more defined physique.
Despite this, other studies in resistance-trained individuals have not shown significant improvements in strength or muscle mass from CLA supplementation alone.

Other Reported Health Effects of CLA

Anti-inflammatory and Immune Modulation

CLA's effects on immune function and inflammation are conflicting. Some studies suggest it can lower pro-inflammatory cytokine production, while high doses have occasionally been linked to increased inflammatory markers.

Impact on Metabolic Health

Data on CLA's impact on insulin sensitivity and blood lipids is also inconsistent.

Some studies indicate supplemental CLA may increase insulin resistance and negatively alter lipid profiles.
The t10, c12 isomer is potentially more concerning in this regard.
Concerns about potential liver fat accumulation with high supplemental CLA amounts have also been raised.

Heart Health and Cancer

Heart Health: Observational studies suggest dietary intake of natural CLA might lower heart disease risk. Supplemental CLA's effect on cholesterol levels is conflicting and sometimes negative.
Cancer: Early animal studies showed potential anti-cancer properties, but human evidence is limited and inconsistent.

The Key Difference: Natural Foods vs. Supplements

The source of CLA significantly impacts its effects.

Natural CLA: Found in low concentrations in grass-fed meat and dairy, primarily as the c9, t11 isomer. It's associated with potential benefits without the negative effects linked to supplements.
Supplemental CLA: Chemically produced from vegetable oils, often with a different isomer ratio and higher amounts of the t10, c12 isomer. Supplemental amounts are much higher than dietary intake and carry a greater risk of adverse effects.

Potential Side Effects and Safety Considerations

While generally recognized as safe by the FDA for certain food uses, higher amounts from supplements can cause side effects.

Common Side Effects: Mild digestive issues like diarrhea, stomach pain, and nausea.
Potential Serious Risks (with high-dose supplements): These include increased insulin resistance, liver fat accumulation, increased inflammation, and negative changes in lipid profiles.

CLA vs. Other Supplements: A Comparison


Feature	CLA	L-Carnitine	Omega-3s (EPA/DHA)
Primary Function	Modest fat loss, muscle preservation	Energy production via fat conversion	Anti-inflammatory, heart health, brain function
Mechanism	Affects fat storage enzymes, increases fat burning	Transports fatty acids to mitochondria for energy	Incorporates into cell membranes, modulates inflammatory pathways
Weight Loss Efficacy	Modest, inconsistent in humans	Supportive for energy, not a primary weight loss agent	Minor indirect effects via metabolism, not a direct weight loss supplement
Primary Sources	Grass-fed meat and dairy	Red meat, avocado	Fatty fish (salmon, mackerel)
Potential Risks	GI issues, potential insulin resistance with high amounts	Generally safe, GI upset with high amounts	Safe at recommended amounts, risk of bleeding with very high amounts

Conclusion: The Modest Role of CLA

The effects of CLA on the body are complex and less dramatic than often claimed. Human research indicates only modest and inconsistent results for fat loss. The source of CLA is critical; natural dietary intake may offer general health benefits, while high-amount supplements carry a greater risk of side effects like insulin resistance and liver issues. CLA can potentially support body composition goals as part of a broader strategy, but it is not a primary solution. For best results, focus on a healthy diet, exercise, and consult a healthcare professional.

For more in-depth information on nutrition and weight loss, consult authoritative sources like the National Institutes of Health.

Frequently Asked Questions

The main dietary sources of CLA are meat and dairy products from ruminant animals like cows, sheep, and goats, with higher levels found in grass-fed varieties. CLA supplements, however, are typically manufactured from vegetable oils.

Some human studies indicate a small, modest reduction in body fat with CLA supplementation, mainly during the first six months. However, many other studies show minimal to no effect, and the results are not as dramatic as those observed in animal research.

CLA is often marketed for muscle growth and preservation. While some studies suggest it can help preserve lean muscle mass, especially with exercise, others have found no significant benefit for strength or muscle gains.

CLA supplements are generally considered safe at recommended amounts, but they can cause mild side effects like gastrointestinal discomfort. Higher amounts have been linked to more serious issues, such as insulin resistance and liver fat accumulation, primarily with the synthetic versions.

Natural CLA from food is predominantly the c9, t11 isomer and is consumed in small amounts. Supplemental CLA is often a chemically altered blend richer in the t10, c12 isomer and taken at much higher amounts, which may be responsible for adverse effects.

CLA supplements are available in various forms, including capsules and softgels. The method of consumption may vary depending on the product and individual preference. It is recommended to follow label instructions or consult a healthcare professional.

The evidence on CLA's effect on metabolic health is mixed and conflicting. Some studies point to potential negative effects like increased insulin resistance, particularly with high supplemental amounts, while others show no significant impact.