Conjugated Linoleic Acid (CLA) is a naturally occurring fatty acid and a structural variant (isomer) of the omega-6 fatty acid linoleic acid. This structural difference, featuring conjugated double bonds, gives CLA unique biological properties. The various forms of CLA are primarily found in the meat and dairy products of ruminant animals, and the compound is widely marketed for its potential to alter body composition and support overall health.
Modifying Body Composition
CLA is perhaps most recognized for its ability to affect the ratio of fat to muscle mass in the body. Research suggests that the compound can contribute to a modest reduction in total body fat mass, particularly in the abdominal area. This effect is largely attributed to the activity of the trans-10, cis-12 (t10,c12) isomer, which is a major component of most commercially available supplements.
At the cellular level, CLA is thought to interfere with fat storage and promote fat breakdown. For example, it may inhibit lipoprotein lipase, an enzyme responsible for transporting fat from the bloodstream into fat cells for storage. Furthermore, the t10,c12 isomer may encourage the programmed cell death (apoptosis) of existing fat cells, reducing the total number of cells available for energy storage.
In addition to reducing fat mass, some human trials indicate that CLA supplementation can help promote the retention or a slight increase in lean muscle mass. CLA may positively influence muscle metabolism and increase overall energy expenditure. This dual action of reducing fat while preserving muscle makes CLA a popular supplement choice for individuals focused on improving their physical physique.
Immune System Support
Beyond its effects on body composition, CLA is recognized for its role in modulating immune function and influencing inflammatory responses. The fatty acid has been studied for its anti-inflammatory properties, particularly the cis-9, trans-11 (c9,t11) isomer. This isomer is the most abundant form found in natural food sources and appears to be the primary agent in immune modulation.
CLA can affect the production of key inflammatory markers, such as specific cytokines and eicosanoids. Studies have shown that CLA supplementation may decrease the levels of pro-inflammatory cytokines like Interleukin-6 (IL-6) and Tumor Necrosis Factor-alpha (TNF-α), suggesting a dampening effect on chronic inflammation. This modulatory role extends to both the innate and adaptive branches of the immune system, potentially offering support for general immune health.
Dietary Sources and Biological Function
The primary natural sources of CLA are the meat and dairy products derived from ruminant animals (cows, sheep, and goats). CLA forms when bacteria in the animal’s rumen process linoleic acid. Products from grass-fed animals typically contain higher concentrations of CLA compared to those from grain-fed animals, as the grazing diet is richer in the linoleic acid precursor.
The CLA found in food is predominantly the c9,t11 isomer, which often accounts for 80% to 90% of the total CLA content. Supplemental CLA, however, is typically produced by chemically altering linoleic acid from vegetable oils, such as safflower oil. This chemical synthesis often results in a mixture of isomers, usually with equal concentrations of the c9,t11 and t10,c12 forms, which allows for a high concentration of the body composition-altering t10,c12 isomer.
Once consumed, CLA acts as a signaling molecule influencing various metabolic pathways. The different isomers have distinct biological functions: the t10,c12 isomer is associated with fat cell metabolism, while the c9,t11 isomer is linked to anti-inflammatory effects. The specific ratio of isomers in a supplement, as opposed to food, dictates the primary effect experienced by the user.
Recommended Dosing and Safety Concerns
The dosage of CLA used in clinical studies that observed positive effects on body composition typically ranges from 3.2 grams to 6.4 grams per day. A minimum daily intake of 3 grams is often cited as the threshold necessary to see a noticeable impact on fat mass. Since the average diet supplies a far smaller amount (usually 15 to 174 milligrams daily), supplementation is necessary to reach the clinically relevant dosage.
CLA supplements are generally considered safe for adults when taken at doses up to 6 grams per day, and the FDA has given CLA a Generally Recognized as Safe (GRAS) status. Despite this, the most commonly reported side effects are gastrointestinal, including stomach upset, nausea, and diarrhea. These mild issues are more likely to occur as the dosage increases.
There are also some concerns regarding the long-term use of high-dose CLA supplements, which may be associated with potential negative effects on glucose metabolism in certain individuals. For people with existing metabolic conditions like diabetes or metabolic syndrome, caution is advised, as CLA may potentially worsen insulin sensitivity. Consulting with a healthcare provider before beginning any CLA supplementation is always recommended to ensure appropriate dosing and to discuss any underlying health concerns.