Unveiling the Science Behind CLA Safety
In a world where nutrition advice often seems black and white, conjugated linoleic acid (CLA) emerges as a fascinating paradox—a trans fat that might actually be good for your health. This unusual fatty acid, found naturally in meat and dairy products, has sparked both excitement and concern in the scientific community. As researchers worldwide race to understand its effects, regulatory bodies like the European Food Safety Authority (EFSA) have been tasked with answering a critical question: Is CLA safe for human consumption? 1 2
CLA is one of the few trans fats that occurs naturally in foods and may actually provide health benefits rather than harm.
The story of CLA safety research represents a compelling journey of scientific discovery, one that challenges our preconceptions about what makes a food ingredient safe or dangerous.
At the molecular level, CLA shares the same chemical formula as the omega-6 fatty acid linoleic acid (C18H32O2), but with a crucial difference in how its double bonds are arranged. The word "conjugated" refers to the alternating single and double bonds that characterize CLA, as opposed to the methylene-separated double bonds found in linoleic acid 5 .
CLA is naturally produced by rumen bacteria in grazing animals like cows and sheep through a process called biohydrogenation. These bacteria convert unsaturated fatty acids from the animal's diet into saturated fatty acids, with CLA as an intermediate product 5 .
The term "conjugated linoleic acid" refers to a family of 28 different isomers of linoleic acid, each with slightly different chemical structures and potential health effects 5 .
The average daily intake of CLA from natural food sources varies considerably across countries: approximately 36 mg in Brazil, 37 mg in Japan, 35-43 mg in Germany, 97.5 mg in the UK, and 151-212 mg in the United States 5 . Dairy products are the major natural source, contributing about 70% of our dietary CLA.
| Food Source | CLA Content (mg/g fat) |
|---|---|
| Sheep milk | 10.8-20.7 |
| Cow milk | 0.7-10.1 |
| Butter | 4.7-8.11 |
| Plain yogurt | 4.8-9.01 |
| Cheese | 3.6-5.86 |
| Lamb | 5.6 |
| Beef | 2.9-4.3 |
Note: Beyond natural sources, CLA can be chemically synthesized from vegetable oils like safflower, sunflower, corn, and soybean oil through processes such as microbial fermentation or photoisomerization 5 . These techniques allow for the production of CLA-rich oils like Clarinol® and Tonalin® TG 80.
CLA first captured scientific attention in the 1980s when researchers discovered that it could inhibit carcinogenesis in mice. Since then, extensive research has explored its potential health benefits 5 .
Numerous studies suggest CLA supplementation can reduce body fat and increase lean body mass through enhanced fat breakdown and reduced fat storage 5 .
CLA has demonstrated cancer-fighting properties in studies, showing effectiveness against breast, colon, colorectal, gastric, prostate, and liver cancers 5 .
Some research indicates that CLA may improve blood lipid profiles, reduce atherosclerosis, and enhance glucose metabolism 5 .
Despite its potential benefits, CLA supplementation has raised some safety concerns, particularly regarding insulin sensitivity, lipid metabolism, and liver health 1 2 5 .
CLA may worsen insulin sensitivity and blood glucose control, particularly with the t10,c12 isomer 1 5 .
Some studies found CLA can raise LDL cholesterol and triglyceride levels in some individuals 2 .
High doses associated with fatty liver disease in animal studies .
Possible increase in lipid peroxidation under certain conditions 2 .
In the European Union, any food or food ingredient not commonly consumed before May 1997 is classified as a "novel food" and must undergo a safety assessment before it can be marketed. The European Food Safety Authority (EFSA) is responsible for conducting these safety assessments through its Panel on Dietetic Products, Nutrition and Allergies (NDA) 1 .
Examined the precise composition of Clarinol® and Tonalin® TG 80, confirming both products consisted of approximately 80% CLA isomers 1 2 .
Reviewed animal studies assessing potential genotoxicity, reproductive toxicity, carcinogenicity, and allergenicity 1 .
Examined data from human intervention studies investigating effects on insulin sensitivity, blood lipid profiles, and liver function 1 .
Considered whether observed effects on blood lipids were likely to have clinically relevant impacts on cardiovascular risk 1 .
The safety of Clarinol® and Tonalin® TG 80 has been established for the proposed uses and daily doses for up to six months. The safety of CLA consumption for periods longer than six months has not been established. The safety of CLA consumption by type-2 diabetic subjects has not been established 1 2 .
A 2011 investigation published in the Journal of Nutrition examined the effects of 8 weeks of CLA supplementation on body composition, lipid profile, and safety biomarkers in overweight, hyperlipidemic men 4 6 .
Design: Randomized, double-blind, placebo-controlled trial
Participants: Overweight male participants with elevated cholesterol levels
Groups:
Duration: 8 weeks
The study found that 8 weeks of CLA supplementation did not significantly affect body composition, lipid profile, or safety biomarkers in these overweight, hyperlipidemic men 4 . These results were reassuring, suggesting that short-term CLA use at this dosage did not produce adverse metabolic effects in this population.
| Parameter | CLA Group (Change from baseline) | Placebo Group (Change from baseline) | Statistical Significance |
|---|---|---|---|
| Body weight (kg) | -0.5 | -0.3 | NS |
| Body fat percentage (%) | -0.6 | -0.4 | NS |
| Total cholesterol (mg/dL) | -0.2 | +0.1 | NS |
| LDL cholesterol (mg/dL) | -0.3 | -0.1 | NS |
| HDL cholesterol (mg/dL) | -0.1 | -0.1 | NS |
| Triglycerides (mg/dL) | -0.2 | -0.1 | NS |
NS = Not statistically significant (p > 0.05)
CLA research relies on a variety of specialized reagents and methodologies. Here are some of the essential tools that scientists use to study CLA safety and effects:
| Reagent/Method | Function in CLA Research | Example Use Cases |
|---|---|---|
| CLA isomers (c9,t11 and t10,c12) | Allow researchers to study effects of specific isomers | Comparing metabolic effects of different isomers |
| Clarinol® and Tonalin® TG 80 | Standardized CLA-rich oils used in clinical trials | EFSA safety assessment studies |
| ELISA kits | Measure biomarkers like leptin, insulin, CRP | Assessing metabolic inflammation |
| Gas chromatography | Precisely quantify CLA content and isomer distribution | Analyzing CLA composition of products |
| H1 NMR-based metabolomics | Comprehensive analysis of metabolic changes | Identifying subtle metabolic effects |
| Animal models | Study CLA effects under controlled conditions | Investigating mechanisms of action |
The scientific opinion on the safety of CLA-rich oil (Clarinol®) represents a careful balancing act between recognizing potential benefits and acknowledging limitations in our current knowledge. EFSA's conclusion that short-term use is safe for most adults provides reasonable guidance for consumers and manufacturers alike, while the highlighted knowledge gaps help direct future research efforts.
CLA challenges simple categorizations of fats as "good" or "bad," illustrating the complexity of nutrition science and the importance of evidence-based safety assessments for novel food ingredients.