Those trying to lose weight are often advised to eat less and move more.

But this advice is often ineffective on its own, and people are failing to reach their goals.

For this reason, many turn to supplements to help them lose weight.

One of these is conjugated linoleic acid (CLA), a natural fatty acid found in meat and dairy products.

Research shows it’s effective for fat loss in animals, but the evidence in humans is less promising.

This article explains what CLA is and if it can help you lose weight.

Man Looking at CLA Supplement

CLA is naturally produced by grazing animals (1).

Cows and other pastured ruminants such as goats and deer have a unique enzyme in their digestive system that converts the omega-6 fatty acids in green plants to CLA (2).

It is then stored in the animals’ muscle tissues and milk.

There are many different forms of it, but the two important ones are called c9, t11 (cis-9, trans-11) and t10, c12 (trans-10, cis-12) (3).

C9, t11 is most abundant in food, whereas t10, c12 is the form most often found in CLA supplements and associated with weight loss. T10, c12 is also present in foods, albeit in much smaller amounts (4).

As the term “trans” implies, this fatty acid is technically a trans fat. But the trans fats found naturally in meat and dairy products are much different than the industrially produced, artificial trans fats found in baked goods and fast food.

Industrially produced trans fats are strongly linked to heart disease, while naturally produced trans fats may be good for you (5, 6, 7, 8).

CLA is not an essential fatty acid, so you don’t need to obtain it from your diet for optimal health. Nevertheless, many people take CLA supplements for their purported fat-burning effects.

Summary CLA is a naturally occurring fatty acid. While it’s not an essential nutrient, it’s commonly taken as a dietary supplement for its purported fat-burning benefits.

Many high-quality studies have analyzed the effects of CLA on fat loss in animals and humans.

However, its fat-burning potential is much stronger in animals than it is in humans.

It Reduces Body Fat in Animals

Research has shown that CLA reduces body fat in animals by increasing the amounts of specific enzymes and proteins that are involved in fat breakdown (9, 10, 11, 12).

One study in mice found that supplementing with CLA for six weeks reduced body fat by 70%, compared to a placebo (13).

CLA has also prevented fat gain in animals and test-tube studies (14, 15, 16, 17).

A study in pigs showed that it decreased fat growth in a dose-dependent manner. This means that increased doses resulted in decreased gains in body fat (18).

These significant findings in animals prompted researchers to test its fat-burning effects in humans.

Human Studies Show Little Weight Loss Benefits

Research in humans shows that CLA has only a modest weight loss benefit.

A review of 18 high-quality, human studies looked at the effects of CLA supplementation on weight loss (19).

Those who supplemented with 3.2 grams per day lost an average of 0.11 pounds (0.05 kg) per week, compared to a placebo.

While these findings were considered significant, this translates to less than half a pound per month.

Several other studies have also looked at the effects of CLA on weight loss in humans.

One review of these studies evaluated its long-term effectiveness on fat loss in overweight and obese participants.

It concluded that taking 2.4–6 grams per day for 6–12 months reduced body fat by 2.93 lbs (1.33 kg), compared to placebo (20).

Similar to previous findings, this loss is relatively small compared to a placebo.

Additional studies have found that CLA has mixed but no real-world benefits on fat loss, even when combined with exercise (21, 22, 23).

Current research suggests that CLA has minimal effects on weight loss in both the short and long term, in addition to potential side effects (24).

Summary In animals, CLA has been shown to burn fat and decrease its formation, leading to significant weight loss. However, in humans, its effect on weight loss is small and holds no real-world benefit.

The safety of CLA supplements has been debated for quite some time.

While some studies have found them to have no adverse effects, the majority of research suggests otherwise (25, 26).

In two meta-analyses, supplementing with CLA was associated with an increase in levels of C-reactive protein, indicating inflammation in the body (27, 28).

On one hand, inflammation is important for fighting off potentially harmful pathogens or initiating tissue repair after a scrape or cut. On the other hand, chronic inflammation is linked to several diseases, including obesity, cancer and heart disease (29, 30, 31).

What’s more, another meta-analysis found supplementing with CLA was associated with a significant increase in liver enzymes, suggesting inflammation or possible liver damage (32).

Importantly, CLA from natural dietary sources is not associated with these effects (7, 8).

This is likely because the CLA found in supplements is different from the naturally occurring CLA found in food.

Of the CLA found in meat and dairy products, 75-90% consists of the c9, t11 form, whereas 50% or higher of the CLA found in supplements consists of the t10, c12 form (33, 34).

For this reason, CLA taken in supplement form has different health effects than CLA that is obtained from the diet.

Therefore, until more research on its safety is available, it should not be taken in large doses or for extended periods.

A safer approach might be to incorporate more CLA-rich foods into your diet.

While you may not reap the same fat loss benefit, doing so allows you to increase your CLA intake from natural sources, which may confer other health benefits.

Summary The form of CLA found in supplements is significantly different than the form that occurs naturally in foods. This may be why CLA supplements have been associated with several negative side effects, while CLA from food has not.

Several studies have shown that people who consume CLA from foods have a lower risk of diseases like heart disease and cancer (35, 36, 37, 38).

Dairy products are the major food sources, but it’s also found in the meat of ruminants (39).

Concentrations of CLA are generally expressed as milligrams per gram of fat.

Foods with the highest amounts include (40, 41, 42):

  • Butter: 6.0 mg/g fat
  • Lamb: 5.6 mg/g fat
  • Mozzarella cheese: 4.9 mg/g fat
  • Plain yogurt: 4.8 mg/g fat
  • Sour cream: 4.6 mg/g fat
  • Cottage cheese: 4.5 mg/g fat
  • Fresh ground beef: 4.3 mg/g fat
  • Cheddar cheese: 3.6 mg/g fat
  • Beef round: 2.9 mg/g fat

However, the CLA content of these foods and food products varies with the season and diet of the animal.

For example, milk samples that were collected from 13 commercial farms had the lowest amounts of CLA in March and the highest amounts in August (43).

Similarly, grass-fed cows produce more CLA than their grain-fed counterparts (44, 45, 46).

Summary CLA is naturally produced in ruminant animals such as cows. The amounts of it produced by these animals are affected by the season and what they eat.

Many ineffective fat-burning supplements are on the market, and the research suggests CLA is one of them.

Its fat-burning effects in animals are impressive but don’t translate to humans.

Besides, the small amount of fat loss that might occur with CLA does not outweigh its potentially harmful effects.

As a safer alternative, it’s likely worthwhile to incorporate more CLA-rich foods, such as dairy or grass-fed beef, into your diet before resorting to CLA supplements.