Conjugated linoleic acid (CLA) is one of those supplements that sounds almost too good to be true. Marketed as a “natural” fat burner found in beef and dairy products, CLA supplements have become popular among people looking for an easy weight loss solution. But as someone who has reviewed the research, I have to be honest: the gap between marketing claims and scientific evidence is significant.

What is Conjugated Linoleic Acid?

CLA refers to a group of fatty acids that are technically trans fats, but not the artificial kind found in processed foods. These naturally occurring trans fats form in the digestive systems of ruminant animals like cattle and sheep, which is why beef and dairy are the primary dietary sources 1.

An average diet provides somewhere between 15 and 174 mg of CLA daily, depending on how much meat and dairy you consume. The CLA in supplements, however, is manufactured from safflower or sunflower seed oil through chemical processing. This distinction matters because the natural form (predominantly the cis-9, trans-11 isomer) differs from the supplemental form, which contains a mix of isomers including the trans-10, cis-12 form 2.

Animal studies painted an optimistic picture early on, suggesting CLA might prevent cancer, improve diabetes markers, protect against cardiovascular disease, and reduce body fat. The problem is that these effects haven’t consistently translated to humans, likely due to differences in dosage, duration of use, and the specific CLA isomers studied.

1. Weight Loss and Body Fat Reduction

Let me address the elephant in the room: weight loss is why most people consider CLA supplements. The marketing is persuasive, often featuring impressive before-and-after images and claims about “melting belly fat.”

The theory behind CLA’s potential fat-reducing effects relates to its proposed ability to influence enzymes involved in fat storage and energy expenditure. Some laboratory studies suggested CLA could inhibit an enzyme called lipoprotein lipase, which helps store fat in cells, whilst potentially increasing fat breakdown 3.

What the research actually shows: A systematic review and meta-analysis pooling data from seven studies with 974 participants found that CLA supplementation did produce statistically significant weight loss compared to placebo. However, and this is the crucial part, the magnitude of weight loss was small and not considered clinically meaningful 4. We’re talking about differences of perhaps a kilogram or two over several months, not the dramatic transformations promised in advertisements.

Another meta-analysis specifically examined whether CLA (from supplements or food sources) affected waist circumference or fasting blood sugar. The finding? No meaningful improvement in either measure 5.

My honest take: If you’re expecting CLA to make a noticeable difference to your weight, you’re likely to be disappointed. The evidence suggests any fat loss is marginal at best. For context, the weight loss you might achieve with CLA is less than what most people experience simply by cutting out sugary drinks or walking an extra 20 minutes daily.

2. Blood Pressure Regulation

High blood pressure affects a staggering proportion of adults over 40, and the consequences of leaving it unchecked are serious: hardening of arteries, reduced blood flow to organs, and increased risk of stroke, heart attack, and kidney failure.

Some researchers hypothesised that CLA might help lower blood pressure. Animal studies were encouraging, suggesting CLA could improve the function of endothelial cells (the lining of blood vessels) and promote the production of nitric oxide, which helps blood vessels relax and widen 6.

What the research actually shows: When researchers pooled data from nine human studies involving 638 participants in a meta-analysis, the results were unambiguous. CLA supplementation had essentially no effect on blood pressure. The average change in systolic blood pressure was -0.03 mmHg and diastolic blood pressure was 0.69 mmHg, neither of which is clinically or statistically meaningful 7.

Reality check: If you have high blood pressure, CLA supplements are not the answer. Evidence-based approaches include reducing sodium intake, maintaining a healthy weight, regular physical activity, limiting alcohol, and medication when lifestyle changes aren’t sufficient.

3. Blood Lipid Management

Dyslipidaemia, or abnormal blood fat levels, is a significant risk factor for cardiovascular disease, diabetes, and stroke. Low-density lipoprotein cholesterol (LDL, often called “bad” cholesterol) receives particular attention because elevated levels contribute to arterial plaque buildup.

Interestingly, this is one area where CLA does show some promise. The same meta-analysis of seven studies with 974 participants mentioned earlier found that CLA supplementation was associated with reductions in LDL cholesterol 4.

The proposed mechanism involves CLA inhibiting apolipoprotein B (a protein that helps transport LDL cholesterol) and increasing the efficiency with which the body clears LDL from the bloodstream.

Worth noting: While this sounds promising, I’d caution against getting too excited. The LDL reduction, whilst statistically significant, was modest. If you’re concerned about cholesterol, options like fish oil, red yeast rice (which contains natural statins), dietary changes, or prescribed medications have stronger evidence behind them. CLA might be a reasonable addition to an existing plan, but it shouldn’t be your first-line approach.

4. Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) has become increasingly common, paralleling rising rates of obesity and type 2 diabetes. The condition involves excessive fat accumulation in liver cells and can progress from simple fatty liver to inflammation, cirrhosis, and even liver cancer if left unmanaged.

Prevalence estimates suggest 20-30% of the general population has some degree of fatty liver, with rates climbing to 70-90% in people who are obese or have diabetes. This makes it the most common chronic liver disease in many countries.

One small controlled study examined whether CLA could help people with NAFLD. The trial lasted eight weeks and involved 38 patients. Those who took CLA combined with vitamin E whilst following a weight loss diet showed greater improvements in several markers compared to the control group: better glycated haemoglobin (HbA1c, a measure of blood sugar control), reduced body fat, improved liver function tests (ALT/AST ratio), better blood lipid ratios (LDL/HDL), and reduced oxidative stress 8.

The catch: This was a single, small study combining CLA with vitamin E and a calorie-restricted diet. We can’t determine how much of the benefit came from CLA versus the other interventions. More importantly, it’s possible most of the improvement came from the weight loss diet itself. Until larger, better-designed studies isolate CLA’s specific contribution, I’d be cautious about recommending it for fatty liver.

Side Effects and Safety Concerns

Here’s where things get more concerning. The CLA from your diet, primarily the cis-9, trans-11 form found naturally in meat and dairy, appears to be safe and may even have some health benefits.

The CLA in supplements is a different story. These products contain primarily the trans-10, cis-12 isomer, and high doses have been associated with several worrying effects in studies:

Insulin resistance: Some research suggests supplemental CLA may impair insulin sensitivity, which is particularly concerning for people at risk of diabetes 9
Effects on lipid profiles: While CLA may lower LDL cholesterol, some studies have found it also reduces HDL (the “good” cholesterol), which isn’t desirable 10
Increased C-reactive protein: CLA supplementation has been linked to elevated inflammatory markers in some studies
Fat redistribution: Rather than overall fat loss, some evidence suggests CLA may cause lipodystrophy, or abnormal redistribution of body fat

Common side effects that users report include digestive issues: diarrhoea, stomach pain, nausea, and flatulence. These tend to be more pronounced at higher doses.

Who Should Avoid CLA Supplements

Certain groups should be particularly cautious or avoid CLA supplements entirely:

Pregnant and breastfeeding women: Insufficient safety data exists for these populations. Given the potential for effects on insulin and lipid metabolism, it’s prudent to avoid supplementation.

People with liver or kidney conditions: Until more is known about how CLA is metabolised in compromised organs, those with liver or kidney dysfunction should consult their doctor before use.

Those taking blood-thinning medications: CLA may slow blood clotting, potentially increasing bleeding risk. If you take warfarin, aspirin, or other anticoagulants, avoid CLA supplements. The same applies before surgery, where it’s recommended to stop CLA at least two weeks beforehand.

People with diabetes or prediabetes: Given the potential for CLA to worsen insulin resistance, those managing blood sugar should be cautious.

How CLA Compares to Other Weight Loss Supplements

If weight loss is your goal, how does CLA stack up against alternatives? Honestly, most weight loss supplements share the same problem: modest effects at best, often with side effects that outweigh benefits.

Garcinia cambogia has similarly underwhelming evidence for weight loss. Green coffee extract showed some promise in early studies but larger trials have been disappointing. Glucomannan, a fibre supplement, may help you feel fuller but won’t cause significant fat loss on its own.

The uncomfortable truth is that no supplement comes close to the effectiveness of eating less, moving more, and maintaining those changes long-term. Supplements that promise effortless weight loss are almost universally disappointing when rigorously tested.

Dosage and Forms

If you still want to try CLA after reading the above, typical supplemental doses in studies range from 1.8 to 7 grams daily, usually divided into multiple doses with meals. Most commercial products provide between 3 and 6 grams per day.

CLA supplements are available as softgels, capsules, or liquid forms. The source is typically safflower oil that has been chemically processed. Some products specify the ratio of the two main isomers (cis-9, trans-11 and trans-10, cis-12), though whether this matters for any potential benefits remains unclear.

Summary

CLA exemplifies a common pattern in the supplement industry: promising animal research followed by disappointing human trials, yet continued marketing based on the initial excitement.

The evidence suggests:

Weight loss effects are minimal and not clinically meaningful
No effect on blood pressure
Modest LDL cholesterol reduction, but questions remain about overall cardiovascular benefit given potential HDL reduction
Very limited evidence for fatty liver, confounded by multiple interventions in the only notable study

Meanwhile, concerns exist about insulin resistance, inflammation, and fat redistribution with long-term supplementation.

If you’re considering CLA for weight loss, your money would likely be better spent on fresh vegetables, a gym membership, or a consultation with a registered dietitian. For cholesterol concerns, discuss evidence-based options with your doctor. The natural CLA in moderate amounts of meat and dairy as part of a balanced diet is likely fine and possibly beneficial, but I wouldn’t bet on supplements to solve your health concerns.

References

Whigham LD, et al. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. Am J Clin Nutr. 2007;85(5):1203-11.
Pariza MW. Perspective on the safety and effectiveness of conjugated linoleic acid. Am J Clin Nutr. 2004;79(6 Suppl):1132S-1136S.
Miner JL, et al. Conjugated linoleic acid (CLA), body fat, and apoptosis. Obes Res. 2001;9(2):129-34.
Whigham LD, et al. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. Am J Clin Nutr. 2007;85(5):1203-11.
Onakpoya IJ, et al. The effect of conjugated linoleic acid on blood lipids: a meta-analysis of randomized controlled trials. Clin Nutr. 2012;31(2):153-9.
Nagao K, et al. Conjugated linoleic acid enhances plasma adiponectin level and alleviates hyperinsulinemia and hypertension in Zucker diabetic fatty rats. Biochem Biophys Res Commun. 2003;310(2):562-6.
Onakpoya IJ, et al. The effect of CLA supplementation on blood pressure: a meta-analysis of randomized controlled trials. Eur J Nutr. 2012;51(3):259-65.
Aryaeian N, et al. The effect of conjugated linoleic acid, vitamin E and their combination on lipid profiles and blood pressure of Iranian adults with active rheumatoid arthritis. Vasc Health Risk Manag. 2008;4(6):1423-32.
Riserus U, et al. Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome. Diabetes Care. 2002;25(9):1516-21.
Whigham LD, et al. Conjugated linoleic acid reduces body fat mass in overweight and obese humans. J Nutr. 2007;137(5):1188-93.