What Are The Side Effects Of CLA?

CLA or Conjugated Linoleic Acid is the name given to a group of linoleic acid isomers that naturally occur in different types of dietary sources, such as; chicken, lamb, pork, and beef. CLA is slightly adapted from linoleic acid (LA) which is an omega-6 fatty acid - possibly holding some importance to overall health. In fact, Conjugated Linoleic Acid is a collective term that is given to a total of 28 distinct isomers - forming when there is a shift between one or both of the double bonds of LA.

Recently rising in popularity as a weight-loss and muscle building dietary supplement, questions about its safety and possible side effects have arisen.

The Discovery Of CLA

CLA was first discovered in 1978 by two researchers, Dr. Michael Pariza and Dr. Mark Cook, from the University of Wisconsin (1). While Pariza was studying the presence of genetic mutation causing compounds in ground beef, the research team found that there was a substance that prevented these mutagen cells from developing. Speculating that this substance would be able to inhibit the activity of cancerous cell mutation.

It was later determined that this was, in fact, the form of lipid fat known as Conjugated Linoleic Acid.

After its discovery, CLA was studied for its potential benefits as an anti-carcinogen when it was found that there was a possible link between this substance and retaining lean muscle, burning fat and speeding up the metabolism.

CLA was discovered in 1978 and was originally studied for its potential as an anti-carcinogen. It was later discovered that there was a link between this substance and weight loss.

Sources Of CLA

CLA is present in dairy products and meats. Particularly, in the muscle fibers and meat of ruminant animals (mammals who absorb nutrients through a fermentation process in their stomachs) (2).

Here are some CLA-rich food sources:

Glass of Yogurt
  • Grass-fed beef
  • Cheese (from grass-fed cow milk)
  • Whole milk (from grass-fed cows)
  • Grass-fed lamb/mutton
  • Plain yogurt
  • Buttermilk
  • Sour cream
  • Turkey
  • Egg yolk
  • Chicken
  • Safflower oil
  • Sunflower Oil
There are many different sources of CLA, predominantly found in ruminant animals, there are some plants that contain this fatty acid.

How CLA Is Produced?

While the human body does not produce its own CLA, it can be obtained by ingesting foods that contain this fatty acid.

In nature, it occurs in grazing animals. These animals have unique enzymes in their digestive tracts which changes linoleic acid found in green plants, into conjugated linoleic acid. After which, the CLA is then stored in their muscle tissue and milk. The level of this free fatty acid in ruminant products used to be much higher - but as these animals are no longer fed green plants, these quantities have diminished significantly (3).

Photo of Sunflower Oil

Due to this, and the increasing concern of animal-welfare - CLA is now synthesized and produced from sunflower and safflower oil. Linoleic acid is also present in some vegetable oils, which is converted into its conjugated form and manufactured into capsules. It should be noted that the safflower used to make CLA typically does not contain pesticides and herbicides.

CLA is produced in animals, through a process where a special enzyme turns linoleic acid into its conjugated form. However, CLA supplements are generally made from safflower oil.

How Does It Work?

CLA is a variation or isomer of linoleic acid. An isomer is a grouping of molecules that possess the same chemical formulation but that is arranged in a different structure. The word conjugated gives a nod to how the isomers are arranged and how they react with electrons. It is this exact interactivity that is the reason for CLA's claimed benefits (4).

Out of the 28 isomers that make up this substance, there are two that have shown the most physiological effect. Namely, cis-9/ trans-11 CLA and trans-10/ cis-12 CLA.

When acting in isolation, these isomers may have body-composition altering effects. Trans-10/ cis-12 CLA has been linked to the reduction of weight and fat gain in the body. While cis-9/ trans-11 CLA is shown to improve the efficiency of feeding and growth. In conjunction, these isomers have a different outcome and have been associated with the inhibition of breast cancer cells in rodents (5).

The isomers that makeup CLA have shown to possess body-composition altering properties. This is attributed to the potential weight-loss benefits of this substance.

How Much You Need

There are many claims to what this substance can do, however, studies on the effects of CLA in humans are still in their infancy. Particularly with regards to the proper dietary amount of CLA required for weight-loss and health benefits.

According to some data, modeled off of the findings in rodent studies, a person weighing approximately 155 pounds would have to take between 3 500 mg and 7000 mg of CLA daily to experience any type of results (6).

The average intake of CLA, through diet, varies from country to country. Unfortunately, there is currently insufficient evidence to support the typical dietary intake of a North American diet. But there is some proof surrounding the advantages of eating different types of CLA-dense food sources.

Due to the drop in the level of CLA found in food sources, getting enough through diet alone might pose a problem. As it is predominantly used as a weight-loss supplement, getting your CLA from foods would be counteractive for its purpose. This is because the food containing this fatty acid is high in calories and greatly fattening.

CLA is a form of fat, which stands to reason that the higher the fat content in foods, the higher the CLA. These calorie dense sources could lead to an increase in weight. High-fat foods should be eaten in moderation as it could also lead to other health issues such as raised levels of cholesterol (7).

Because eating these foods can have the weight gaining consequences, the audience most interested in this substance (dieters) often opts for dietary supplements instead.

CLA safflower oil supplements usually contain around 1000 mg per capsule, which provides higher levels of this substance without the caloric intake.

Glass of Fresh Milk

In order to get the same amount of this substance (as that of a single serving, 1000 mg capsule) you would need to eat:

  • More than six cups of grass-fed cow's milk
  • Approximately 10 ounces of grass-fed beef
  • Roughly one and a half pounds of cheese
  • More than 22 cups of whole milk
  • 20 cups of ice cream

However, this is just an indication of the amount needed to meet 1000 mg. Studies that have investigated the proper quantity needed for weight loss, suggest that between 3000 mg and 8000 mg doses of CLA would most likely be effective.

The effective amount of CLA you need varies from person to person. But it is believed that between 3000 mg and 8000 mg should be taken daily.

CLA For Weight Loss

In pill form, CLA has been coined as the 'miracle weight loss solution'. With most research surrounding this substance now investigating its effects on health and fat-loss. Unfortunately, these studies have found more potential for weight-loss in animals (rodents) than in humans.

The findings outlined that CLA can reduce fat in animals through a process where a specific enzyme and protein becomes activated. Assisting in the breakdown of fat. A study, conducted in 1998, focused on the effects that conjugated linoleic acid had on the metabolism and body fat of mice. Its conclusion was that CLA was able to reduce the fat percentage by 70% after six weeks and inhibited fat gain.

In turn, these results spurted the interest surrounding what role this substance could play in human weight-loss. However, there has only been moderate results when applied to a human system, with only mediocre weight-loss benefits recorded. Participants in one study, who took approximately 3.2 grams of CLA daily, lost an average of half a pound of fat per month.

While there have been several additional studies investigating the link between CLA and weight - current research does suggest that even with exercise there is a minimal outcome. And it has uncovered potential side effects of this weight-loss aid.

Studies have produced only minimal proof of CLA related weight-loss in humans. However, these results were positive in animal subjects.

Safflower Oil CLA Side Effects

Today, the most common source of CLA found in dietary supplements is derived from safflower oil. It should be noted that there are some health impacts associated with the use and ingestion of this oil (8).

While safflower is likely safe when taken by the mouth, for most people, some of the potential threats include:

Male Checking His Blood Sugar
  • Increased Bleeding: Those suffering from hemorrhagic diseases, stomach ulcers or clotting conditions should avoid using safflower - as it can slow down clotting and increase bleeding.
  • Allergic Reaction: There is a possibility that safflower can trigger an allergic reaction in people who are sensitive to plants of the Asteraceae/Compositae family. These plants include marigolds, ragweed, and daisies.
  • Diabetes: There is evidence to suggest that safflower could increase blood sugar levels, interfering with the body's ability to control sugar in the blood. Particularly in diabetics.
CLA safflower oil side effects may include increased bleeding, allergic reaction, and risk of diabetes. It should be taken with caution.

Possible CLA Side Effects

According to the FDA, this substance is 'generally regarded as safe' and is likely not to cause any major adverse reactions - when taken by mouth in amounts found naturally in foods. It is also possibly safe when taken in medicinal amounts but side effects have been recorded.

While a handful of studies claim that there are no adverse effects relating to the use of CLA, research does suggest otherwise.

CLA side effects could include:

  • Upset stomach
  • Nausea
  • Headache
  • Backache
  • Fatigue
  • Diarrhea
  • Increased risk of bleeding
  • Liver toxicity (9)
  • Increased blood sugar


There are mixed findings on whether this substance actually raises the levels of sugar in the blood and decreases the body's sensitivity to insulin. Due to the inconsistencies in the existing evidence, it is highly advisable to speak to your healthcare provider before taking CLA as a diabetic or prediabetic.

High Potassium

Some proof suggests that CLA can increase potassium levels in the body. And while for most this is no concern, those suffering from hypertension or kidney diseases could experience dangerously high levels of potassium - which can lead to serious health problems.

Heart Problems

Female Holding Heart Figure

According to evidence put forward by the University of Pittsburgh Medical Center, CLA could prevent the normal function of blood vessels. This is due to an increase in the c-reactive protein. An annular, pentameric protein that is found in blood plasma and has been linked to inflammation - which ups the risk of cardiovascular diseases.


The effects that this fatty acid has on the reduction of fat in the body is said to reduce the fat content in breast milk. Effectively resulting in infants consuming insufficient amounts of the calories and nutrients needed. This can lead to problems surrounding proper childhood development and growth (10).

When it comes to the safety of use, there are some precautions and warnings:

  • Children can possibly take CLA safely for up to seven months. In medicinal amounts, by mouth.
  • Pregnant or breastfeeding women are likely out of danger when ingesting this substance from food sources. But is advised to avoid use in medicinal amounts.
  • Those suffering from bleeding disorders should stay away from CLA, as it might increase the risk of bleeding by interfering with the blood's ability to clot. This applies to surgeries as well. This substance should not be taken at least two weeks prior to a procedure.
  • As a diabetic, CLA could worsen your diabetes and should not be used.
  • Sufferers of metabolic syndrome should note that there are concerns related to the use of CLA and it should be taken with caution.
Because CLA is produced from safflower oil, it shares many of the same possible side effects. Potential heart problems, increased risk of diabetes, high potassium levels and dangers for breastfeeding women are all included in the potential dangers.

The Takeaway

The safety of Conjugated Linoleic Acid is widely debated. With studies finding both positive, neutral and negative evidence surrounding its use.

It has been associated with the increase of the inflammatory C-Protein (which causes inflammation in the body). And while inflammation does assist with fighting off pathogens and aiding in tissue repair, it can lead to obesity, cancer, heart disease, and liver damage.

When consumed through meats and dairy products, there is no evidence to suggest adverse effects. However, as the CLA typically consumed by the average person is synthesized from safflower oil - taking this as a dietary supplement (before more evidence is available) should not be done in large doses or for long periods of time.

While CLA is rising in popularity in the health and fitness community, there is not enough evidence about this substance and the possible risks it poses, to conclusively evaluate its effectiveness and safety. It has been determined that the conjugated linoleic acid found in food sources might have some benefits to your health. Although these foods should also be consumed in moderation. As a result of the uncertainty surrounding this substance, it is always advisable to consult your doctor or medical professional before you start taking it.
Brought to you by our expert team at Authority Health.

Jennie is a qualified clinical psychologist with a strong focus on CBT, especially for clients suffering the symptoms of PTSD and depression.

She fulfilled her dream by graduating from the Mannheim University in Germany which specializes in the research of Cognitive Psychology and draws from the teachings of both Freud and Jung. To accomplish her Ph.D, she attended the University of Pennsylvania to follow in the footsteps of Dr. Aaron Becks who created CBT and REBT therapy programs. She qualified several years ago and brings a fresh, unique, young approach to treatment plans and behavioral programs.   

Jennie attends as many conferences as she can and is eager to always learn more in her field of expertise. She loves to surf and travel.