Conjugated Linoleic Acid (CLA) is a naturally occurring fatty acid primarily found in the meat and dairy products of ruminant animals. The average human diet contains only a small amount of CLA, leading to its popularity as a dietary supplement. Most commercial CLA supplements are not sourced directly from these foods. Instead, they are synthesized from vegetable oils, most commonly safflower or sunflower oil, through a chemical process that concentrates the fatty acid into a potent form.
Understanding CLA Isomers and Sourcing
CLA is not a single compound but describes a family of at least 28 different positional and geometric isomers of linoleic acid. These isomers are chemically distinct molecules that share the same formula but have different structures. The two isomers that have been the subject of nearly all scientific study are cis-9, trans-11 (c9, t11) and trans-10, cis-12 (t10, c12).
The c9, t11 isomer is the principal form found naturally in foods like beef and dairy, sometimes referred to as rumenic acid. The t10, c12 isomer is the form typically targeted and concentrated in supplements due to its specific physiological effects. Supplements are manufactured by chemically altering linoleic acid, usually from safflower oil, to create a mixture that often contains roughly equal amounts of these two primary isomers. The specific effects associated with CLA supplementation are dependent on this isomer difference.
Primary Reasons for Supplementation
Consumers primarily seek CLA supplements for their potential to modify body composition. The most frequently cited use is the reduction of body fat mass, which is largely attributed to the action of the t10, c12 isomer. This specific isomer is thought to act on fat cells, or adipocytes, by inhibiting the uptake of lipids and stimulating fat breakdown.
CLA is also taken with the goal of retaining lean muscle mass, especially during periods of weight loss or calorie restriction. Research suggests that while the effects on overall weight loss are modest, CLA may help shift the ratio of fat to muscle. These effects on body composition are the main drivers for the supplement’s popularity in the fitness and weight management communities.
Key Criteria for Selecting a Top Supplement
Selecting a high-quality CLA supplement requires careful inspection of the product label beyond the total CLA content. The concentration of active CLA isomers is a primary concern, as products often contain fillers. A reputable supplement should have a total active isomer concentration of 75% to 85% of the total oil content. For individuals focused on body composition changes, the ratio of the two main isomers is paramount.
The t10, c12 isomer is associated with fat mass reduction, so a top-tier supplement will transparently list a high concentration of this specific isomer. Achieving a meaningful effect requires a specific daily dosage. Most human clinical trials use a range of 3.2 grams to 6.4 grams of active CLA per day. This amount must be the active isomer dose, not the total softgel weight, and should be split across meals throughout the day.
Transparency and manufacturing integrity are also important factors in supplement selection. The presence of third-party testing or certification from organizations like NSF or USP verifies that the product’s contents match the label claims and ensures purity. Without this external validation, there is no guarantee that the label accurately reflects the isomer ratio or the total active dosage.
Important Safety and Usage Considerations
While CLA is considered safe when taken at studied doses, users should be aware of side effects and long-term risks. Mild gastrointestinal issues are the most common adverse effects, including stomach upset, nausea, and diarrhea. These digestive issues often occur at higher doses but are not considered severe.
A more serious concern involves negative metabolic changes, particularly at elevated doses. Some human studies indicate that CLA supplementation may worsen insulin sensitivity and negatively affect glucose metabolism in certain individuals. Furthermore, there is evidence that CLA, especially the t10, c12 isomer, can reduce levels of HDL, or “good,” cholesterol, which is a factor for cardiovascular health.
Individuals with pre-existing metabolic conditions, such as diabetes or metabolic syndrome, should approach CLA with caution due to the risk of impaired blood sugar control. Pregnant or breastfeeding women, as well as those with known liver conditions, are advised to avoid CLA due to a lack of safety data and reports of liver fat accumulation in some studies. It is always advisable to consult a healthcare provider before starting any new supplement regimen, especially when aiming for doses in the upper range.