Does CLA have any benefits? A deep dive into the science and risks

Naturally found in the meat and dairy products of ruminant animals, Conjugated Linoleic Acid (CLA) has been extensively studied for its potential health effects, though research has yielded mixed results, especially in humans. This has many asking: Does CLA have any benefits that make supplementation worthwhile?

Quick Summary

An examination of conjugated linoleic acid, exploring its purported effects on body composition and other health markers, along with the notable risks and limitations found in human research. The findings contrast promising animal studies with modest and often inconsistent human trial outcomes.

Key Points

• Modest Weight Loss: Clinical trials suggest CLA supplements provide only a modest, statistically small reduction in body fat, with effects often inconsistent and plateauing over time.

• Natural vs. Supplemental Sources: CLA found naturally in grass-fed meat and dairy has a different isomer profile and is likely safer than supplements made from vegetable oils, which contain higher levels of the potentially harmful t10,c12 isomer.

• Metabolic Risks: High doses of supplemental CLA can potentially lead to adverse metabolic effects, including increased insulin resistance, inflammation markers (like CRP), and fat accumulation in the liver.

• Inconsistent Health Benefits: Research on other purported benefits, such as enhanced immunity, heart health, and cancer prevention, shows mixed or limited results in human studies compared to more promising findings in animals.

• Safety Profile: While generally considered safe in food amounts, CLA supplements can cause mild side effects like digestive upset. Concerns exist regarding potential long-term risks at higher supplemental doses, especially for individuals with metabolic conditions.

What is CLA?

Conjugated linoleic acid (CLA) is a naturally occurring fatty acid found in the fat of ruminant animals like cows, goats, and sheep. It is technically a form of trans fat, but natural CLA in food amounts is not considered harmful. CLA exists as different isomers, with cis-9, trans-11 (c9,t11) being predominant in natural sources. CLA supplements, however, are typically produced from chemically altered vegetable oils and contain a mixture of isomers, including significant amounts of trans-10, cis-12 (t10,c12). Different isomers can have distinct biological effects and potential risks.

The Modest Effects of CLA on Weight and Body Composition

CLA has been widely studied for its effects on weight loss and body composition. While animal studies showed promising fat-reducing effects, human studies have been much less conclusive. Research suggests CLA may influence fat breakdown and accumulation, and potentially increase energy expenditure.

A meta-analysis from 2007 indicated that a daily dose of 3.2 grams of CLA resulted in a small fat loss of about 0.09 kg per week compared to placebo. A 2019 review noted that while some studies found statistically significant reductions in body fat, their clinical significance was unclear due to the small effect size. The weight loss effect, when observed, often plateaus after about six months. Some studies have found no effect on weight at all. Furthermore, some research suggests CLA may primarily reduce subcutaneous fat rather than visceral fat, a pattern potentially linked to adverse metabolic outcomes. The significant fat loss seen in animal studies has not translated reliably to humans.

Exploring Other Potential Health Benefits of CLA

CLA has also been investigated for potential benefits beyond weight management, though the evidence is varied.

Immune System Modulation

Some research suggests CLA may impact the immune system. Primarily in animals, studies indicate a potential to reduce pro-inflammatory cytokines and enhance immune responses. Human studies are less conclusive but hint at potential reductions in inflammatory markers and possible benefits for conditions like rheumatoid arthritis, requiring further research.

Heart Health

Animal studies have suggested CLA may help prevent hardening of the arteries. However, human trials on cholesterol and blood lipids show mixed results. While dietary CLA from grass-fed products might be associated with better heart health markers, supplemental CLA has sometimes been linked to decreased "good" HDL cholesterol.

Cancer Prevention

Early animal research showed potential anti-cancer effects. Some observational human studies have found an association between higher dietary intake of natural CLA (from dairy) and a reduced risk of certain cancers, such as breast and colorectal cancer. However, clinical trials using CLA supplements in humans have not provided enough consistent evidence to recommend CLA for cancer prevention.

Potential Risks and Side Effects of CLA Supplements

CLA supplementation, especially at high doses, is associated with potential risks. It's important to differentiate between natural food sources and concentrated supplements.

Metabolic Side Effects

A key concern is the potential negative impact on metabolic health. Studies suggest that supplemental CLA, particularly the t10,c12 isomer, can induce insulin resistance, which may increase the risk of type 2 diabetes, especially in individuals with existing metabolic syndrome.

Inflammation and Liver Health

CLA supplements may also raise markers of inflammation, such as C-reactive protein (CRP). Some animal studies have shown that high doses can lead to increased fat in the liver. Human data on liver function is less severe but suggests potential risks.

Common Digestive Issues

Common side effects of CLA supplements include digestive problems such as nausea, stomach upset, diarrhea, and indigestion. These are typically mild but can be uncomfortable.

Natural CLA vs. Supplemental CLA

Feature	Natural CLA (from Foods)	Supplemental CLA
Source	Meat and dairy from ruminants (especially grass-fed)	Chemically altered vegetable oils (e.g., safflower oil)
Isomer Profile	Predominantly cis-9, trans-11 (c9,t11)	Approximately equal mixture of c9,t11 and t10,c12 isomers
Daily Intake	Very small amounts (e.g., 150-212 mg in the US)	High doses (typically 3-6 grams)
Observed Effects	Associated with lower risk of some diseases in observational studies; likely beneficial in food amounts	Modest, inconsistent weight loss; potential for adverse metabolic effects

A Balanced Conclusion on CLA Benefits

So, does CLA have any benefits that are reliably proven? For most people, especially with high-dose supplements, the benefits appear modest and may be outweighed by potential risks. While animal studies are promising, human trials for weight loss show inconsistent and minor effects compared to lifestyle changes like diet and exercise.

Awareness of potential metabolic side effects, such as insulin resistance and increased inflammation, is important, particularly with synthetic supplements containing the t10,c12 isomer. Consuming natural food sources like grass-fed beef and dairy is generally considered a safer way to increase CLA intake for potential health benefits. As with any supplement, consult a healthcare provider before starting CLA to discuss risks and interactions.

References

The following resources provide further information on CLA's effects, risks, and research findings {Link: Verywell Health https://www.verywellhealth.com/conjugated-linoleic-acid-weight-loss-3231585}.

Frequently Asked Questions

What is CLA used for?

CLA is most commonly marketed and used as a dietary supplement for weight loss, specifically for reducing body fat and potentially increasing lean muscle mass. It is also investigated for other potential benefits related to immunity and metabolic health, although the evidence is often inconsistent.

How does CLA help with weight loss?

Animal studies suggest CLA can reduce body fat by increasing fat breakdown, stimulating energy expenditure, and inhibiting fat production. In humans, these effects appear to be much more modest and less consistent, resulting in only minor reductions in body fat.

Is CLA safe to take?

In amounts found naturally in food, CLA is considered likely safe. However, in higher supplemental doses, it can cause side effects like digestive upset, and some studies raise concerns about potential adverse metabolic effects, such as increased insulin resistance and inflammation.

What is the difference between natural and supplemental CLA?

Natural CLA comes from ruminant meat and dairy, with a dominant c9,t11 isomer profile. Supplemental CLA is synthetically made from vegetable oils and contains a roughly 50:50 mixture of c9,t11 and t10,c12 isomers. The t10,c12 isomer is more strongly linked to adverse metabolic effects.

Can CLA build muscle?

Some studies, particularly in conjunction with exercise, have suggested that CLA may help improve body composition by increasing lean muscle mass. However, the evidence is not definitive, and many studies show no significant effect on strength or muscle growth.

What are the common side effects of CLA supplements?

Reported side effects include stomach upset, diarrhea, nausea, and fatigue. More serious potential side effects, particularly at high doses and with specific isomers, include insulin resistance, lower HDL cholesterol, and increased inflammation.

Is CLA beneficial for heart health?

Evidence regarding CLA's heart health benefits is mixed. While some animal studies show anti-atherogenic effects, some human studies have found that supplemental CLA can lower 'good' HDL cholesterol levels, which is a negative outcome for cardiovascular health.