CLA vs L-Carnitine: What to Choose and for Whom

CLA and L-carnitine are bought mainly with one goal - to lose weight. However, the profiles of people for whom these supplements may be at least a little useful or, on the contrary, undesirable, differ substantially. The editorial team offers a practical guide: what can realistically be expected, who is better off refraining, and how to assess a product if the decision to buy has already been made.

Realistic expectations from both supplements

Before choosing, it is worth honestly looking at the scale of the effect. A meta-analysis by Whigham et al. (2007) showed that CLA at a dose of about 3.2 g per day reduces fat mass by roughly 0.09 kg per week compared with placebo. Over three months this is a few hundred grams of fat - noticeably less than a moderate calorie deficit gives.

For L-carnitine, a meta-analysis by Pooyandjoo et al. (2016) found a moderate reduction of body weight compared with control, which weakened over time. There are few studies, they are heterogeneous, and participants often simultaneously followed a diet, which complicates assessing the contribution of the supplement itself.

So neither CLA nor L-carnitine is a “fat burner” in the everyday sense. They do not compensate for overeating and do not create an energy deficit on their own. At best they are a small addition to already established nutrition and activity.

Such an assessment does not mean the supplements are useless for everyone. But the choice between them should be based not on advertising promises but on the person's profile, their health and those additional effects that have at least a limited evidence base.

Who L-carnitine may be appropriate for

The first group can be considered people who eat little or no red meat: vegetarians and vegans. Their body synthesizes carnitine from lysine and methionine, and clinical deficiency in healthy people usually does not occur, but their intake from food is significantly lower. For this group, carnitine is one of the supplements where the difference from the diet is at least theoretically justified.

The second group is people who do resistance training and are interested in recovery. A study by Volek et al. (2002) showed that intake of L-carnitine tartrate had a favorable effect on markers of recovery after intense squats, in particular on indicators of muscle damage. This is a small study, but it explains the popularity of precisely the tartrate form in sports products.

The third group is endurance athletes who are ready for prolonged intake. A study by Wall et al. (2011) showed that only 24 weeks of carnitine intake together with a large amount of carbohydrates raised the carnitine content in muscle and changed fuel use during exertion. For most people such a protocol is impractical because of the additional calories from carbohydrates.

Separately, it is worth mentioning people with medical indications - for example, patients on hemodialysis or with congenital metabolic disorders. For them, levocarnitine is a medicinal product, and the decision on its prescription and dosage is made exclusively by a doctor.

Who CLA may be appropriate for

CLA may be considered by people without carbohydrate metabolism disorders who are already losing weight through nutrition and activity and want to add a small potential effect. It is precisely under such conditions that most of the studies included in the meta-analyses were conducted.

Adherents of the “natural” approach should know that CLA from food (dairy products, beef) is represented mainly by the cis-9,trans-11 isomer, whereas in supplements about half is trans-10,cis-12. So it is practically impossible to obtain the dose used in studies from diet alone, but the effects of natural CLA are also not equivalent to those of supplements.

People who tolerate fatty supplements poorly should take into account possible digestive disorders reported in studies. Taking it with food usually reduces such manifestations.

At the same time, the editorial team believes that for most people the benefit of CLA is too small for it to become a priority expense. If the budget is limited, money spent on quality food, protein or a consultation with a dietitian will give a greater result.

Who is better off refraining

For people with insulin resistance, prediabetes or type 2 diabetes mellitus, the editorial team does not recommend CLA without a doctor's consultation. A study by Risérus et al. (2002) showed that the trans-10,cis-12 isomer in men with obesity and metabolic syndrome reduced insulin sensitivity, that is, it acted in the direction opposite to the desired one.

People with high cardiovascular risk should also discuss the intake of L-carnitine with a doctor. A study by Koeth et al. (2013) linked the metabolism of carnitine by the gut microbiota with the formation of TMAO, which was associated with atherosclerosis. Although direct harm of ordinary supplements to humans has not been proven, caution in risk groups is justified.

• Pregnancy and breastfeeding - safety data for both supplements are limited.
• Kidney and liver disease - any supplements only after a consultation.
• Taking anticoagulants or thyroid medications - possible interactions should be clarified with a doctor.
• Eating disorders - “fat burners” can reinforce unhealthy weight-control strategies.

It is also worth refraining from combined “fat-burning” products with an unknown composition. Often CLA or carnitine in them is merely a cover for stimulants whose doses are not always stated honestly, and for athletes this is also a risk of violating anti-doping rules through contaminated products.

Doses from studies and product selection

For CLA, the most data concerns doses of about 3–4 g per day of the isomer mix, distributed across several intakes together with food. The meta-analysis by Whigham et al. (2007) cites 3.2 g per day as a benchmark. Increasing the dose beyond this level did not show a proportional strengthening of the effect but may increase adverse reactions.

For L-carnitine, weight-loss and recovery studies most often used about 2 g per day. In the work of Wall et al. (2011), carnitine was combined with a large serving of carbohydrates, which is critical for raising its content in muscle; without such accompaniment, uptake by muscle is limited.

When choosing a product, pay attention to the form. For CLA, the label should state the CLA content per serving, not just the volume of oil in the capsule. For carnitine, the specific form (L-carnitine, tartrate, acetyl-L-carnitine) and the amount of L-carnitine specifically, since in tartrate part of the mass is tartaric acid.

Avoid products that do not state the isomer composition or the form of carnitine, and those that promise “minus 10 kg in a month.” For athletes undergoing doping control, independent batch certification is important.

Editorial conclusions

L-carnitine has a somewhat wider range of potentially appropriate scenarios: a plant-based diet, recovery after strength exertion, medical indications under a doctor's supervision. CLA is appropriate mainly as a small addition to weight loss in people without carbohydrate metabolism disorders.

Both supplements give a modest effect on body weight and do not replace a calorie deficit, protein in the diet and regular activity.

People with insulin resistance should avoid CLA without a consultation, and those with high cardiovascular risk should discuss the intake of carnitine with a doctor.

We broke down the biochemistry of both substances in the material “CLA vs L-carnitine: what's the difference.” We also recommend reading “Taurine vs betaine: what to choose and for whom” and “EAA vs whey protein: what to choose and for whom.”

References

1. Whigham LD, Watras AC, Schoeller DA. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. Am J Clin Nutr. 2007;85(5):1203–1211.
2. Pooyandjoo M, Nouhi M, Shab-Bidar S, Djafarian K, Olyaeemanesh A. The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials. Obes Rev. 2016;17(10):970–976.
3. Volek JS, Kraemer WJ, Rubin MR, et al. L-Carnitine L-tartrate supplementation favorably affects markers of recovery from exercise stress. Am J Physiol Endocrinol Metab. 2002;282(2):E474–E482.
4. Wall BT, Stephens FB, Constantin-Teodosiu D, et al. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. J Physiol. 2011;589(Pt 4):963–973.
5. Risérus U, Arner P, Brismar K, Vessby B. Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome. Diabetes Care. 2002;25(9):1516–1521.
6. Koeth RA, Wang Z, Levison BS, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013;19(5):576–585.
7. Onakpoya IJ, Posadzki PP, Watson LK, Davies LA, Ernst E. The efficacy of long-term conjugated linoleic acid (CLA) supplementation on body composition in overweight and obese individuals: a systematic review and meta-analysis of randomized clinical trials. Eur J Nutr. 2012;51(2):127–134.