What is Conjugated Linoleic Acid (CLA)?
Conjugated Linoleic Acid, or CLA, is a naturally occurring type of omega-6 fatty acid found mainly in the meat and dairy products of ruminant animals like cows and sheep. It is technically a naturally occurring trans fat, but it is chemically different from the industrial trans fats linked to negative health outcomes. While the CLA found in food occurs primarily as the cis-9, trans-11 isomer, most commercial supplements are produced synthetically by chemically altering linoleic acid from vegetable oils, like safflower oil, to create a mixture of different isomers. These supplemental isomers can have distinct and sometimes less favorable effects compared to the naturally occurring ones.
The Role of CLA in Weight Management and Body Composition
The most common use of CLA is for weight loss and improving body composition, with much of the initial interest coming from promising animal studies. Animal models showed significant reductions in body fat, which fueled supplement market growth. However, the results in humans have been far more modest and inconsistent, and in some cases, insignificant.
Several mechanisms are proposed for CLA's action on body fat, though the evidence is debated. Potential mechanisms include:
- Increasing Energy Expenditure: CLA might slightly increase the body's basal metabolic rate (BMR), leading to more calories burned throughout the day.
- Inhibiting Lipogenesis: Some research suggests CLA, particularly the trans-10, cis-12 isomer common in supplements, can inhibit the enzyme lipoprotein lipase, which plays a key role in fat storage.
- Enhancing Lipolysis: CLA might help increase the breakdown of fat stores, making it more available for the body to use as fuel.
- Promoting Apoptosis: Animal studies have shown CLA can trigger the death of fat cells in white adipose tissue, though this hasn't been consistently demonstrated in humans.
A 2019 meta-analysis of human trials found that CLA supplementation led to only a modest reduction in body fat mass, averaging about 0.2 pounds per week over six months. The effects tend to plateau after the initial period and may not be considered clinically significant for weight loss in many individuals. Some studies noted that CLA's effects might be more pronounced in those who are overweight or obese, or when combined with exercise. However, even in these cases, the results are small and unreliable, with the weight loss often coming from subcutaneous rather than the more dangerous visceral fat.
Other Health Claims and Research Findings
Beyond body composition, CLA has been studied for a range of other potential health effects, but much of the evidence remains inconclusive or mixed, particularly in human trials.
Supporting Muscle Mass
Some studies, often alongside resistance training, have found a small increase in lean body mass or preserved muscle during weight loss. However, other studies show no such effect. This muscle-sparing effect is one reason for CLA's popularity among athletes, but its ergogenic value is still debated. The effect seems to be relatively small and not always reproducible across all study populations.
Metabolic and Immune Function
CLA is suggested to have anti-inflammatory and immune-modulating properties. Animal studies show potential benefits, but human research is often conflicting. Some studies have explored its effects on insulin sensitivity, with mixed results and even negative outcomes reported with high doses or certain isomers. The impact on cholesterol and blood lipids is also contentious; while some studies show modest improvements, others report negative changes like reduced HDL ("good") cholesterol.
Dietary vs. Supplemental CLA
There is a critical distinction between the CLA obtained from food and that found in supplements. Naturally occurring CLA, found in grass-fed ruminant products, is mostly the cis-9, trans-11 isomer, which is linked to potential health benefits in some observational studies. In contrast, supplemental CLA is synthesized from vegetable oils, resulting in a different isomeric blend, typically a 50:50 mix of the cis-9, trans-11 and trans-10, cis-12 isomers.
| Feature | Dietary CLA (from food) | Supplemental CLA (from pills) |
|---|---|---|
| Source | Ruminant meat and dairy (especially grass-fed) | Chemically altered linoleic acid from vegetable oils |
| Isomer Composition | Predominantly cis-9, trans-11 | Roughly 50:50 mixture of cis-9, trans-11 and trans-10, cis-12 |
| Dosage | Low, part of a balanced diet | High, typically 3-6 grams per day |
| Safety Profile | Generally considered safe and beneficial as part of a healthy diet | Higher doses carry potential risks, including metabolic side effects |
Risks, Dosage, and Considerations
While CLA is often marketed as a safe weight loss aid, caution is warranted, especially with high-dose supplements. Dosages in studies typically range from 3 to 6 grams per day. Common, but usually mild, side effects can include:
- Stomach upset
- Nausea
- Diarrhea
- Headaches
- Fatigue
More concerning side effects have been noted in some studies, particularly in individuals with pre-existing conditions. For example, high-dose CLA has been linked to potential increases in insulin resistance and negative changes in lipid profiles (lowering "good" HDL cholesterol) in some susceptible populations. High supplemental doses, especially of the trans-10, cis-12 isomer, have also been associated with increased fat accumulation in the liver in animal models, a stepping stone to metabolic syndrome. Individuals with diabetes or metabolic syndrome should be particularly cautious and consult a doctor. The long-term safety of high-dose CLA supplementation is not fully established.
For those interested in the potential health benefits, a more prudent approach may be to increase dietary intake of naturally occurring CLA through grass-fed ruminant products rather than relying on high-dose supplements with their associated risks and inconsistent results. Always speak with a healthcare professional before starting any new supplement regimen.
Conclusion
What do you use CLA for? Primarily, it's marketed for its potential to help with weight management and improve body composition, though the clinical evidence in humans shows only modest and inconsistent results. Some people also use it for potential benefits to muscle growth, immune function, and metabolism, but the supporting research is often mixed and limited. Crucially, the effects and safety profile of high-dose synthetic CLA supplements differ significantly from the natural CLA found in foods from grass-fed animals. While moderate doses appear generally safe for many, potential side effects, including on metabolic markers, exist, especially at higher levels. Therefore, a decision to use CLA should be made with a full understanding of the mixed evidence and consultation with a healthcare provider.
For a deeper dive into the metabolic effects, refer to this review: A review on effects of conjugated linoleic fatty acid (CLA) upon body composition and energetic metabolism.
