Conjugated linoleic acid (CLA) is a type of fatty acid found naturally in certain foods. It is primarily present in meat and dairy products from ruminant animals like cows, sheep, and goats. It is also widely available as a dietary supplement. It is a family of linoleic acid isomers with several structural forms.
Purported Health Claims of CLA
CLA supplements are commonly marketed with various health benefits, particularly those related to body composition. A primary claim is its ability to reduce body fat and aid in weight loss. Manufacturers also promote CLA for potentially increasing lean muscle mass and boosting metabolism. Beyond body composition, other purported benefits include modulating immune function and promoting general health. These claims highlight CLA’s potential to alter how the body stores and utilizes fat.
Scientific Analysis of Weight Management Claims
Scientific studies on CLA’s effects on weight management present a more nuanced picture, often contrasting with initial findings from animal models. In animal studies, CLA has shown significant effects, such as reducing body fat, burning fats, and interfering with fat production. However, human clinical trials have yielded more modest and sometimes inconsistent results regarding weight and fat loss.
For instance, a review of 15 studies found that overweight individuals supplementing with CLA for at least six months experienced only an average loss of about 1.5 pounds (0.7 kg) more than control groups. Some human trials have indicated a modest reduction in body fat mass, especially in overweight individuals, but not necessarily a decrease in overall body weight or Body Mass Index (BMI). A meta-analysis examining CLA combined with exercise noted a significant decrease in body fat (standardized mean difference, -0.42) and improved insulin resistance, though no reduction in body weight was observed.
The effectiveness of CLA can also depend on the specific isomers present in the supplement. Most supplements contain a mixture of isomers, with trans-10,cis-12 (t10,c12) and cis-9,trans-11 (c9,t11) being the most abundant and studied. The t10,c12 isomer is often associated with the anti-obesity effects seen in some research, while the c9,t11 isomer is more linked to other potential health benefits.
Examination of Other Potential Health Effects
Beyond weight management, research has explored CLA’s impact on lean muscle mass, immune system modulation, and cardiovascular health markers. Some studies suggest CLA may increase lean body mass, though evidence for a substantial effect on muscle growth in humans is not universally strong. Regarding the immune system, CLA supplementation may modulate immune function, though more comprehensive studies are needed to fully understand this effect.
For cardiovascular health, initial animal models suggested beneficial effects on cardiometabolic disease. Human studies have investigated CLA’s influence on blood pressure and lipid profiles. While CLA may reduce blood pressure when taken with certain medications, it does not consistently lower blood pressure on its own. Similarly, studies on lipid profiles have shown mixed results, with some indicating potential negative changes like increased LDL or lipoprotein(a).
Safety and Potential Side Effects
While generally considered safe when taken within typical dosages, CLA supplementation can lead to various side effects. Common and mild issues include digestive problems such as nausea, stomach pain, gas, and diarrhea.
More serious concerns have emerged from some research, particularly with higher doses or long-term use. CLA has the potential to negatively affect liver health, with some studies indicating possible liver damage. CLA may also influence insulin sensitivity, potentially worsening insulin resistance or negatively impacting glucose metabolism. Additionally, CLA could increase inflammatory markers or negatively alter lipid profiles, such as increasing LDL cholesterol or lipoprotein(a) and decreasing HDL cholesterol.
Supplement Forms and Dosage
Conjugated linoleic acid supplements are typically derived from plant oils, such as safflower oil, rather than directly from animal products. These supplements usually contain a specific mixture of CLA isomers, often including both the cis-9,trans-11 (c9,t11) and trans-10,cis-12 (t10,c12) forms. The proportions of these isomers can vary between products.
Scientific studies commonly use CLA dosages ranging from 3 to 6 grams per day, with some research employing doses between 1.6 to 6.8 grams for periods up to 12 months. When considering a CLA supplement, it is advisable to look for products from reputable manufacturers. Reputable manufacturers often provide third-party testing for purity and potency, ensuring the product contains the stated amount and type of CLA isomers.