Conjugated Linoleic Acid | What Is CLA & How Does It Work?

Omega-3 fatty acids have created a huge buzz in the worlds of health and fitness. These essential fatty acids cannot be synthesized within the body and as such need to be consumed for their benefits to be seen.

However, with the storm of interest enveloping Omega 3’s, everyone seems to have forgotten their misunderstood cousin; Omega 6 fatty acids. In fact this type of fatty acid gets a bad rep as they are pro-inflammatory and are linked to the development of certain diseases (1).

However, this article aims to open your eyes to one of this group which may be worth your consideration to include in your daily supplement regime. This article will open your eyes to Conjugated Linoleic Acid.

What is Conjugated Linoleic Acid?

Back in 1978, a researcher by the name of Dr Michael Pariza, working at the University of Wisconsin, made a novel discovery (2). When he was examining grilled ground beef (as you do) to confirm the presence of compounds which could cause genetic mutations (mutagens); his team discovered that there was also a substance which prevent the development of mutagen cells (mutagenesis).

beef steak CLA Conjugated Linoleic Acid | What Is CLA And What Does It Do?

He very wildly speculated that this substance could actually inhibit the activity of the most devastating pathological form of cell mutation- cancer! This substance was later discovered to be a form of lipid (fat), called Conjugated Linoleic Acid (CLAS) (3).

What is the science behind CLA?

CLA is a family of 28 different isomers of linoleic acid. Linoleic acid is the shortest chain, omega-6 polyunsaturated fatty acid (meaning they have more than one double bond in their back bone).

An isomer is a group of molecules with the same chemical formula (same number and type of atoms), but arranged into a different structure. In essence, CLA is a group of different variations of linoleic acid.

The “conjugated” part refers to the arrangement of their single and double bonds in their structure, and how their electrons will interact due to this structure. It is this specific electron interactivity which is considered to facilitate some of the proposed benefits of CLA.

There are two main isomers which are thought to show the most physiological effect (4):

Cis9,trans11-CLA (we will call t11)


trans-10, Cis12-CLA (we will call t10).

Interestingly, when acting alone, both these isomers have an effect on the body which may influence body composition. t10 has been shown to be responsible of reduction in body fat gains (5); whilst t11 actually enhances feeding efficiency and growth (4).

Then, when they work together, there is a different outcome. Working in juxtaposition both t10 and t11 have been seen to be effective in inhibiting breast cancer cells in rodents (6-8).

Needless to say, the biological effects of CLA seem to be due to a number and variety of interactions with our bodies’ metabolic pathways. Most CLA supplements will be composed of these two isomer forms.

Sources of CLA

CLA is found in diary (non-skimmed) products and meat. More specifically it is found in the meat from ruminant animals (e.g. animals such as cows and lamb that absorb nutrients in a specialised stomach by fermenting plant based food, such as grass).

Conjugated Linoleic Acid | What Is CLA And What Does It Do? steak

The typical daily dietary intake has been found to be approximately 97g per day in the United Kingdom (9). This is much less than that seen in the USA (150g in men) (10), and in Germany (350g-430g) (11).

As an example, concentrations of the t11 isomer of CLA in various foods in the UK have been shown to be(9).:

✓ 210mg/ 100g of mature cheddar cheese compared to 38mg/ 100g of cheese spread

✓ 201mg/ 100g of butter compared to 3.5mg/ 100g of margarine

✓ 7.3g/100g full fat milk compared to 3.3g in semi skimmed milk and ZERO in skimmed milk

✓ 127mg/ 100g of a cooked beef burger compared to a 62.1g/ 100g of a fast food beef burger

✓ 276.8mg/ 100g of lamb mince (or of a lamb donor kebab)

What are the benefits of CLA?

Conjugated Linoleic Acid | What Is CLA And What Does It Do? fat burning

CLA supplementation has been proposed to provide various health benefits.

These benefits include:

✓ Boosting of the Immune System

A group of 71 healthy males were provided different supplement forms of CLA in a double blind, randomised controlled trial (12). Each group was provided with a supplement in soft gel form of CLA in three different ratios of the t11 and t10 isomers. The participants were also then given a hepatitis B vaccination and their immune system response was measured.

In the group who were provided a ratio of CLA isomers which was 50:50, an increase in immune response in the way of twice as many protective anti-bodies was seen. This suggests this preparation of CLA (50% t11 and 50% t10) may assist immune system response to illness, or may prevent against the negative effects of overtraining.

✓ Potential Cancer Growth Prevention

As already suggested, the original benefits considered for CLA were for their mutagenesis inhibition properties (e.g. reducing cancer cell growth).

Studies have demonstrated that when a mixture of various forms of CLA isomers is fed to animals; tumour cell growth in the breast, skin and colon is reduced. The inhibition of carcinogenesis is suggested to involve the reduction in number of cells proliferating, changes to the cell growth cycle, and facilitation of cancel cell death (13).

✓ Management of blood lipid and blood sugar levels

Animal studies in obese and diabetic rats suggest a negative effect of consuming CLA for those with diabetes, due to reductions in the level of blood sugar and insulin concentration. A study involving 16 young (mean age 21 years old) and sedentary participants aimed to measure the effect of CLA on insulin sensitivity in humans (14).

After an 8 week period of CLA supplementation (4g/ day) insulin sensitivity index increased, and fasting insulin levels reduced; compared to a placebo supplement which showed no change. Thus these results indicate that the supplement showed an improvement in the participants’ responses to an oral glucose tolerance test; and reduces insulin resistance (increases insulin sensitivity).

It would mean you need less carbs to be consumed to increase blood sugar levels, facilitate insulin release and subsequently transfer glucose to your cells for energy metabolism.

The more efficient this process is, the less chance carbs will be stored as FAT.

✓ Fat burning benefits…

CLA and Fat Burning

The documented benefit of CLA in reducing body fat is explained by two main theories.

Conjugated Linoleic Acid | What Is CLA And What Does It Do? fat burning

1) The first is the reduction of lipid uptake into adipocytes (fat cells) by inhibition of a specific enzyme called lipoprotein lipase (15-16). This mechanism is facilitated predominantly by the t10 isomer of CLA (16).

2) The second mechanism considered is the proposed benefit of CLA in reducing the accumulation of triacylglycerol in fat cells. Triacylglycerol is a blood lipid which enables transfer of glucose and fat from the liver.

In animal model studies on mice CLA was found to reduce accumulation of triacylglycerol in fat cells (17). This benefit was also seen in cultures of human cells with the t10 isomer (18-19).

A separate study demonstrated that fat loss in rats fed a CLA supplement is due to a reduction in size of fat cells by 15 to 29% compared to controls (20).

These results indicate the CLA can reduce both synthesis and storage of fat cells, as such reducing levels of body fat in both animal and human laboratory models.

Further studies on CLA fat burning

Another benefit found is that in an animal model a CLA supplemented diet increased oxygen consumption and energy expenditure, leading to greater fat burning capacity in the skeletal muscle tissue (15, 21).

As such, this indicates that CLA can potentially not only reduce body fat; but then also assists removing fatty deposits in our muscles.

CLA: Less Fat, More Muscle

Conjugated Linoleic Acid | What Is CLA And What Does It Do?

Interestingly in both animal (15) and human (22-23) models, changes in body fat do not alter weight loss. This is even when body fat is reduced up to 60% (15)! In fact, body fat loss has also been seen alongside increases in protein synthesis (24).

Therefore if the reason for taking CLA supplements is to sustain or lose weight for competitive sport (e.g. for a weight class in combat sports), it is perhaps a fruitless endeavour.

Instead, it seems more appropriate to consume CLA if your aim is more aesthetic, and body fat loss is your goal alongside maintenance of lean body mass (independent of weight loss). This is obviously more apparent when consumed in combination with physical activity (17).

CLA + ? = Better Results!

Recently a study examining 37 recreationally trained females showed that when consumed alongside a thermogenic, a protein gel and a multi-vitamin supplement, significant improvements were seen in a number of physical outcomes (25).

Conjugated Linoleic Acid | What Is CLA And What Does It Do?

Assessment of fat percentage via DEXA scan and skin fold measurements showed approximately 3% changes in body fat percentage, and skinfold thickness in 5 areas of the body (chest, waist, hip, shoulder blade and triceps).

Incidentally, this study also demonstrated that the combination of supplements used also led to an approximate 3kg reduction in body weight.

CLA Dosage

Doses used across studies are inconsistent varying from as low as 1.4g per day to 6.8g per day. Studies examining the correct dosage and safety of this supplement show that no additional effect is seen on body fat mass beyond doses of approximately 3.2 to 3.4g per day (26-27).

The supplement can be easily taken via CLA powder of which one serving would provide a 3g dose, or via 1g CLA soft gels taken 3 times per day.

CLA Safety 

As with any supplement consumed for health reasons all possible ventures to assess the risk of toxicity need to be evaluated.

In the case of CLA the overarching evidence supports that adverse effects have not been observed (17, 28) and that CLA supplements are non-toxic (29).

Concerns regarding the influence of CLA on insulin sensitivity are unsubstantiated (30-32); as are suggestions that CLA may enhance inflammatory aspects of cardiovascular disease (33).

Take Home Message

If you training objectives are based around sustaining lean muscle mass and shedding body fat then CLA may be the supplement for you. A course of CLA should gain best results alongside a suitably intense training regime to shred unwanted fat, whilst helping you maintain your hard earned muscle bulk.

Whether via a powder addition to a pre-workout shake or via soft gels consumed at meal times, 3-4g per day is all you need to boost the potential to burn fat!

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