What is Conjugated Linoleic Acid (CLA)?
Conjugated linoleic acid (CLA) is a naturally occurring polyunsaturated omega-6 fatty acid. It is not a single entity but a group of at least 28 different isomers of linoleic acid. These isomers are characterized by having double bonds in a conjugated arrangement, which influences their biological activity. The primary dietary form is the cis-9, trans-11 isomer, also known as rumenic acid, which is primarily found in ruminant animal products. The trans-10, cis-12 isomer is another important variant, often synthesized in supplements. Interest in CLA began in the late 1980s when researchers identified its potential health benefits, particularly its anticarcinogenic properties, in studies involving cooked ground beef.
Dietary Examples of Natural CLA
The most significant sources of natural CLA in human diets come from animals, particularly ruminants. The CLA content in these products is substantially influenced by the animal's diet, with grass-fed animals producing significantly higher amounts.
Meat Products from Ruminants:
- Beef: Especially from grass-fed cattle, beef is a notable source of CLA.
- Lamb (Mutton): Studies show that lamb and mutton can have some of the highest concentrations of CLA among red meats.
- Veal: This meat also contains good levels of CLA.
Dairy Products from Ruminants:
- Milk: The CLA content in milk varies widely depending on the animal's diet and species, with milk from sheep and goats often containing higher levels than cow's milk. Organic and grass-fed dairy typically contain more CLA.
- Butter: As a concentrated milk fat product, butter is a reliable source of CLA.
- Cheese: Various types of cheese, including Swiss, Blue, and Cheddar, contain CLA, with levels influenced by milk source, fermentation, and ripening time.
- Yogurt: Fermented dairy products like yogurt can have their CLA content altered by the starter cultures used in the fermentation process.
Other Natural Sources:
- Eggs: The CLA content in eggs can be increased if the laying hens are fed a CLA-enriched diet.
- Certain Mushrooms: Some edible mushrooms are known to contain small, but rare, amounts of CLA.
- Plant-based Precursors: Pomegranate seeds contain punicic acid, which can be converted to a form of CLA (rumenic acid) in the body after absorption.
Supplemental and Fortified Examples of CLA
Because the amount of natural CLA obtained from food is often insufficient to produce the effects seen in many clinical trials, supplements are a popular alternative.
- Safflower and Sunflower Oils: The CLA in most supplements is not derived from natural food but is produced by chemically altering linoleic acid found in vegetable oils like safflower and sunflower oil.
- Fortified Foods: Some food products, such as milk or yogurt, may be fortified with CLA to increase their content, though availability can vary by region.
- Dietary Supplements: A variety of supplement brands offer CLA, often as a weight management or muscle-toning aid. These typically contain a roughly 50:50 mixture of the cis-9, trans-11 and trans-10, cis-12 isomers.
Natural vs. Supplemental CLA
There are key differences between the CLA found naturally in food and the CLA produced synthetically for supplements.
| Feature | Natural (Dietary) CLA | Supplemental CLA |
|---|---|---|
| Source | Ruminant animals (e.g., beef, lamb, dairy), with content influenced by grass-fed diets. | Chemically altered linoleic acid from vegetable oils like safflower oil. |
| Isomer Ratio | Primarily consists of the cis-9, trans-11 isomer (rumenic acid), which is the most common natural form. | Typically contains a roughly 50:50 mix of the cis-9, trans-11 and trans-10, cis-12 isomers. |
| Dosage | Relatively low, often providing hundreds of milligrams per day. | Significantly higher, with studies often using doses of 3-6 grams per day. |
| Health Effects | Linked to improved metabolic health and lower disease risk in observational studies. | Associated with a modest fat-loss effect in some clinical trials, but also potential side effects like liver fat accumulation at high doses. |
Conclusion
Examples of CLA are most abundant in the fatty tissues and milk products of ruminant animals, particularly those raised on grass-based diets. The concentration of this beneficial fatty acid in foods like grass-fed beef, lamb, and dairy can be significantly higher than in products from grain-fed animals. For individuals aiming for higher intakes, dietary supplements produced from vegetable oils offer concentrated doses, although the isomer composition and potential effects differ from natural sources. Both natural food sources and supplements provide examples of CLA for those interested in its health-promoting properties, but understanding their differences is crucial for effective and safe use. For detailed scientific reviews on CLA's effects, a search on databases like PubMed Central is recommended.
