Understanding CLA and the Daily Question
Conjugated linoleic acid (CLA) is a type of omega-6 fatty acid naturally found in the meat and dairy products of ruminant animals, such as cows and sheep. Its status as a popular weight loss and bodybuilding supplement has led many to question its safety for daily, long-term consumption. While the CLA from natural food sources is considered safe, the high-dose synthetic CLA in supplements is a different product with varying effects. The key difference lies in the balance of isomers, which are specific chemical forms of CLA. Naturally occurring CLA is predominantly the cis-9, trans-11 isomer, whereas supplements typically contain a roughly 50:50 mix of the cis-9, trans-11 and trans-10, cis-12 isomers. It is the trans-10, cis-12 isomer that has been linked to potential adverse effects in some studies.
The Health Benefits and Modest Results
CLA's appeal stems from potential health benefits identified in animal studies, such as modest reductions in body fat and anti-inflammatory properties. However, the results from human trials have been mixed and often less dramatic than those seen in animals. For example, a 2020 review suggested that taking 3.2–3.4 grams of CLA per day for at least six months could result in a slight reduction in body weight. Other meta-analyses, however, concluded that the effects on weight loss and fat mass were not clinically significant. Some evidence indicates that CLA may help improve body composition by increasing lean body mass, particularly when combined with exercise. The discrepancy in results between animal and human studies can be attributed to differences in dosage, duration, and the type of CLA isomer used.
Potential Risks and Side Effects of Daily CLA
While the FDA has given CLA a 'Generally Recognized as Safe' (GRAS) status for certain foods in specific amounts, this does not apply broadly to all supplements or dosages. Doses used in studies typically range from 3 to 6 grams per day, with some suggesting this range is safe for up to a year. Nevertheless, higher doses increase the risk of side effects, which can range from mild to serious.
Common Mild Side Effects:
- Stomach upset
- Diarrhea or loose stools
- Nausea
- Fatigue
- Headache
Potential Severe Side Effects (especially with higher doses or long-term use):
- Increased inflammation: Studies in both animals and humans have revealed that CLA can drive inflammation. One study observed increases in markers of inflammation, such as C-reactive protein (CRP) and IL-6, at higher doses.
- Impaired glucose metabolism: Concerns exist that CLA supplementation can worsen insulin resistance, especially in individuals with metabolic syndrome or diabetes.
- Fatty liver: Large doses of supplemental CLA have been linked to increased fat accumulation in the liver, which is a risk factor for metabolic syndrome and diabetes.
- Lowered HDL cholesterol: Some human studies have shown that CLA can lower 'good' HDL cholesterol levels.
- Increased oxidative stress: The trans-10, cis-12 isomer has been shown to markedly elevate lipid peroxidation, a marker of oxidative stress.
Who Should Avoid Daily CLA Supplementation?
Because of the potential risks, certain populations should be cautious or completely avoid daily CLA use. This includes:
- Individuals with diabetes or metabolic syndrome
- People with bleeding disorders or those taking blood-thinning medication
- Women who are pregnant or breastfeeding
- Children, as long-term safety data is lacking
- Anyone with pre-existing heart or liver conditions
CLA vs. Diet: Sources and Impact
| Feature | Supplemental CLA | Natural Dietary CLA |
|---|---|---|
| Source | Chemically altered linoleic acid from vegetable oils like safflower | Naturally present in meat and dairy from ruminant animals |
| Isomer Composition | Often a 50:50 mix of c9,t11 and t10,c12 isomers | Primarily the c9,t11 isomer |
| Dose | High, typically 3 to 6 grams per day | Low, typically 15–212 mg per day |
| Known Effects | Modest, often unreliable effects on weight/fat loss, potential side effects | Associated with lower risk of chronic diseases in observational studies |
| Safety Concerns | Long-term use and high doses raise concerns about liver fat, insulin resistance, and inflammation | Considered safe and beneficial within a balanced diet |
Conclusion: Weighing the Risks and Benefits
Is it safe to take CLA every day? For many healthy individuals, the answer appears to be yes, provided the dosage is kept within the typically studied range of 3 to 6 grams per day and for a limited duration, such as 6 to 12 months. However, the potential for modest fat loss must be weighed against the known and unknown risks, especially for long-term use. The CLA found in supplements is different in composition and concentration from the CLA obtained naturally through a balanced diet, and this synthetic form is associated with side effects like stomach upset and potential increases in markers for inflammation. Furthermore, people with existing health conditions like diabetes, metabolic syndrome, or bleeding disorders should avoid supplemental CLA entirely due to significant health risks. Before beginning any daily supplement regimen, it is crucial to consult with a healthcare provider to ensure it is the right choice for your individual health profile and goals.
Authoritative Reference
For an in-depth, peer-reviewed review of the pre-clinical and human trials on CLA, consider reviewing the publication by L.J. den Hartigh.
