Conjugated linoleic acid (CLA) is a naturally occurring fatty acid that has garnered attention for its potential health benefits, including effects on metabolism and body composition. Humans primarily obtain CLA through consuming animal-based foods and by taking dietary supplements. These sources differ in origin: natural CLA is a byproduct of animal digestion, while synthetic CLA is manufactured from plant oils. Understanding these origins clarifies how CLA enters the food supply.
Natural Sources: Ruminant Products
The most significant and bioavailable source of CLA is the meat and milk from ruminant animals like cows, sheep, and goats. CLA is not found in their feed but is created in the rumen during digestion through a two-step process involving microbial action and tissue enzymes.
The Role of Ruminant Digestion
Ruminant animals' multi-chambered stomachs and the bacteria within the rumen, such as Butyrivibrio fibrisolvens, facilitate CLA production. These bacteria biohydrogenate polyunsaturated fatty acids from the animals' diet, like linoleic acid from grass, into more saturated fats. CLA is an intermediate compound in this process.
The Impact of Animal Diet
An animal's diet directly affects the CLA concentration in their products. Grass-fed animals tend to have higher CLA levels in their meat and dairy compared to grain-fed animals. Diets rich in linoleic and alpha-linolenic acids from pasture increase precursor availability for ruminal CLA production. Grain-heavy diets can lead to lower CLA levels by altering the ruminal environment.
Manufactured Sources: Dietary Supplements
Dietary supplements provide an alternative source of CLA. Unlike the naturally occurring CLA in animal products, supplement CLA is commercially produced through a process called alkaline isomerization.
The Sourcing and Synthesis Process
Most CLA supplements are made from vegetable oils high in linoleic acid, such as safflower, sunflower, and corn oils. Linoleic acid undergoes chemical alteration to create a mixture of CLA isomers, typically including c9,t11 and t10,c12.
Isomer Differences and Biological Effects
Natural CLA from ruminants is predominantly the c9,t11 isomer. Supplements generally contain a mixture with a near 1:1 ratio of c9,t11 and t10,c12 isomers. These variations in isomer composition may result in different biological effects.
Comparison of CLA Sources
This table outlines the key distinctions between natural and synthetic sources of conjugated linoleic acid.
| Feature | Natural CLA (from Ruminants) | Synthetic CLA (from Supplements) |
|---|---|---|
| Primary Source | Meat and dairy from grass-fed cows, sheep, goats | Vegetable oils (e.g., safflower, sunflower, corn) |
| Production Process | Microbial biohydrogenation in animal rumen and endogenous tissue synthesis | Chemical isomerization in a lab setting |
| Key Isomer(s) | Predominantly c9,t11 (rumenic acid) | Approximately 1:1 ratio of c9,t11 and t10,c12 |
| Concentration | Varies widely based on animal's diet, generally lower | Consistent, higher concentrations suitable for specific dosing |
| Form | Part of whole foods (e.g., meat, cheese, butter) | Concentrated, often in softgel capsules or oils |
| Benefits | Health effects potentially tied to specific isomer profile | Effects associated with combined isomer ratio, with some variations noted |
Beyond Ruminants: Other Sources
Besides ruminant products and supplements, other sources contain smaller amounts of CLA. These include meats from monogastric animals like chickens and pigs, trace amounts in certain fish and marine oils, and some plant-based items like white button mushrooms and pomegranate seed oil. Additionally, some food-grade microorganisms, including Lactobacillus and Bifidobacterium, can produce CLA through fermentation and are used to create enriched dairy products.
Conclusion
The primary source of CLA for humans is meat and dairy from ruminant animals, especially grass-fed ones, produced naturally by gut bacteria. Synthetic CLA supplements, derived from vegetable oils, provide a concentrated dose but have a different isomer profile. Minor sources include non-ruminant meats, certain plants, and probiotic bacteria. The choice depends on dietary needs.
To explore the biological effects and variations of CLA further, you can consult resources such as {Link: ScienceDirect https://www.sciencedirect.com/science/article/abs/pii/S1871141316302682}.
