Not all fats are created equal.

Some of them are simply used for energy, while others have powerful health effects.

Conjugated linoleic acid (CLA) is a fatty acid found in meat and dairy that is believed to have various health benefits (1).

It is also a popular weight loss supplement (2).

This article examines CLA’s effect on your weight and overall health.

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Linoleic acid is the most common omega-6 fatty acid, found in large amounts in vegetable oils but also in various other foods in smaller amounts.

The “conjugated” prefix has to do with the arrangement of the double bonds in the fatty acid molecule.

There are 28 different forms of CLA (3).

The difference between these forms is that their double bonds are arranged in various ways. It's important to keep in mind that something as minuscule as this can make a world of difference to our cells.

CLA is essentially a type of polyunsaturated, omega-6 fatty acid. In other words, it’s technically a trans fat — but a natural type of trans fat that occurs in many healthy foods (4).

Numerous studies show that industrial trans fats — which are different from natural trans fats like CLA — are harmful when consumed in high amounts (5, 6, 7).

Summary CLA is a type of omega-6 fatty acid. While it is technically a trans fat, it’s very different from the industrial trans fats that harm your health.

The main dietary sources of CLA are the meat and milk of ruminants, such as cows, goats and sheep.

The total amounts of CLA in these foods varies greatly depending on what the animals ate (8).

For example, the CLA content is 300–500% higher in beef and dairy from grass-fed cows than grain-fed cows (9).

Most people already ingest some CLA through their diet. The average intake in the US is about 151 mg per day for women and 212 mg for men (10).

Keep in mind that the CLA you find in supplements is not derived from natural foods but made by chemically altering linoleic acid found in vegetable oils (11).

The balance of the different forms is heavily distorted in supplements. They contain types of CLA never found in large amounts in nature (12, 13).

For this reason, CLA supplements do not provide the same health effects as CLA from foods.

Summary The main dietary sources of CLA are dairy and meat from cows, goats and sheep, whereas CLA supplements are made by chemically altering vegetable oils.

The biological activity of CLA was first discovered by researchers who noted that it could help fight cancer in mice (14).

Later, other researchers determined that it could also reduce body fat levels (15).

As obesity increased worldwide, interest grew in CLA as a potential weight loss treatment.

In fact, CLA may be one of the most comprehensively studied weight loss supplement in the world.

Animal studies suggest that CLA may reduce body fat in several ways (16).

In mouse studies, it was found to reduce food intake, increase fat burning, stimulate fat breakdown and inhibit fat production (17, 18, 19, 20).

CLA has also been studied extensively in randomized controlled trials, the gold standard of scientific experimentation in humans — though with mixed results.

Some studies indicate that CLA can cause significant fat loss in humans. It may also improve body composition by reducing body fat and increasing muscle mass (21, 22, 23, 24, 25).

However, many studies show no effect at all (26, 27, 28).

In a review of 18 controlled trials, CLA was found to cause modest fat loss (29).

The effects are most pronounced during the first six months, after which fat loss plateaus for up to two years.

This graph shows how weight loss slows down over time:

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According to this paper, CLA can cause an average fat loss of 0.2 pounds (01. kg) per week for about six months.

Another review gathered that CLA caused about 3 pounds (1.3 kg) more weight loss than a placebo (30).

While these weight loss effects may be statistically significant, they are small — and there is potential for side effects.

Summary Though CLA supplements are linked to fat loss, the effects are small, unreliable and unlikely to make a difference in everyday life.

In nature, CLA is mostly found in the fatty meat and dairy of ruminant animals.

Many long-term observational studies have assessed disease risk in people who consume larger amounts of CLA.

Notably, people who get a lot of CLA from foods are at a lower risk of various diseases, including type 2 diabetes and cancer (31, 32, 33).

Additionally, studies in countries where cows predominantly eat grass — rather than grain — show that people with the most CLA in their bodies have a lower risk of heart disease (34).

However, this lower risk could also be caused by other protective components in grass-fed animal products, such as vitamin K2.

Of course, grass-fed beef and dairy products are healthy for various other reasons.

Summary Many studies show that people who eat the most CLA have improved metabolic health and a lower risk of many diseases.

Evidence suggests that getting small amounts of natural CLA from food is beneficial.

However, the CLA found in supplements is made by chemically altering linoleic acid from vegetable oils. They are usually of a different form than the CLA found naturally in foods.

Supplemental doses are also much higher than the amounts people get from dairy or meat.

As is often the case, some molecules and nutrients are beneficial when found in natural amounts in real foods — but become harmful when taken in large doses.

Studies indicate that this is the case with CLA supplements.

Large doses of supplemental CLA can cause increased accumulation of fat in your liver, which is a stepping stone towards metabolic syndrome and diabetes (35, 36, 37).

Numerous studies in both animals and humans reveal that CLA can drive inflammation, cause insulin resistance and lower “good” HDL cholesterol (38, 39).

Keep in mind that many of the relevant animal studies used doses much higher than those people get from supplements.

However, some human studies using reasonable doses indicate that CLA supplements may cause several mild or moderate side effects, including diarrhea, insulin resistance and oxidative stress (40).

Summary The CLA found in most supplements is different from the CLA found naturally in foods. Several animal studies have observed harmful side effects from CLA, such as increased liver fat.

Most studies on CLA have used doses of 3.2–6.4 grams per day.

One review concluded that a minimum of 3 grams daily is necessary for weight loss (40).

Doses of up to 6 grams per day are considered safe, with no reports of serious adverse side effects in people (41, 42).

The FDA allows CLA to be added to foods and gives it a GRAS (generally regarded as safe) status.

However, bear in mind that the risk of side effects increases as your dosage increases.

Summary Studies on CLA have generally used doses of 3.2–6.4 grams per day. Evidence suggests it doesn’t cause any serious adverse effects at doses up to 6 grams per day, but higher doses increase the risks.

Studies suggest that CLA has only modest effects on weight loss.

Although it doesn’t cause any serious side effects at doses up to 6 grams per day, concerns exist about the long-term health effects of supplemental doses.

Losing a few pounds of fat may not be worth the potential health risks — especially as there are better ways to lose fat.