CLA and Sleep

The editorial team regularly receives the questions «can CLA be taken at night» and «does it interfere with sleep». Unlike caffeine-containing fat burners, conjugated linoleic acid is not a stimulant. But that does not yet mean there is no connection with sleep at all. We examine what is known for certain and what remains an assumption.

Does CLA have a stimulating effect

CLA is a fatty acid, a close relative of the ordinary linoleic acid from vegetable oils. It does not act on adrenergic receptors, does not block adenosine receptors like caffeine, and does not raise catecholamine levels. Therefore it has no direct stimulating effect on the central nervous system.

The mechanisms proposed to explain CLA's effect on adipose tissue lie in the plane of metabolism: an effect on lipogenesis enzymes, lipoprotein lipase, adipocyte differentiation, and also on the apoptosis of fat cells in rodents. None of these processes is associated with the acute activation that a person would feel in the evening as «I can't fall asleep».

That is precisely why in classic CLA studies insomnia does not figure among the typical side effects. Most often participants complained of digestive discomfort — nausea, bloating, loose stools. These complaints are important for the topic of sleep, but they act by a completely different route than stimulants.

So, if a person sleeps poorly after «CLA capsules», the first thing to check is the composition of the product. In many complexes CLA is combined with caffeine, green tea extract, or guarana, and then the sleep disturbance is explained precisely by these components.

What research says about sleep

Let us say straight away: the editorial team did not find quality randomized studies in which sleep was the main outcome of taking CLA. In such work sleep was either not assessed or recorded only as part of a general list of adverse events.

In large long-term studies, for example the year-long study by Gaullier and colleagues (2004) in overweight people, the tolerability profile of CLA was generally satisfactory, and the main complaints concerned digestion. Sleep disturbances were not a characteristic problem.

In animal models, on the other hand, there are isolated data on the effect of fatty acids on circadian rhythms and metabolism at night, but transferring them to humans is incorrect. The editorial team does not recommend trusting texts that promise CLA «improves sleep» or «burns fat in your sleep»: there is no evidence base for such claims.

So, the honest answer is this: a direct effect of CLA on sleep has not been proven, either in a positive or a negative direction. All that can be discussed are the indirect routes, which will be covered next.

Indirect ways of affecting nighttime rest

The first and most practical route is gastrointestinal tolerability. CLA at doses of 3–6 g per day means several large soft oil capsules. Taken on an empty stomach or right before bed, in sensitive people they can cause belching, heartburn, or a feeling of heaviness, and this is already a real factor in poor falling asleep.

The second route is body weight. Excess weight, especially in the neck and abdomen area, is a known risk factor for obstructive sleep apnea. However, CLA's effect on fat mass in humans is small: the meta-analysis by Whigham and colleagues (2007) estimated it at about 0.09 kg per week. One should not count on CLA noticeably relieving apnea.

The third route is metabolic. There are data that the trans-10, cis-12 isomer may worsen insulin sensitivity in people with metabolic syndrome (Risérus et al., 2002). Disorders of carbohydrate metabolism are broadly associated with worse sleep quality, but no one has studied the direct chain «CLA → insulin → poor sleep».

The fourth route is psychological. A person on a strict diet who takes CLA most often sleeps worse because of hunger and a calorie deficit, and not because of the supplement itself. It is important not to attribute to the supplement effects that are actually caused by the eating regimen.

When to take CLA so as not to interfere with sleep

In most studies the daily dose of CLA was divided into 2–3 intakes together with food. This approach reduces the likelihood of digestive complaints and does not tie the supplement to a particular time of day, since the effect, if any, accumulates over weeks, not hours.

For people with a sensitive stomach or a tendency to reflux, the editorial team advises moving the last intake to dinner, which takes place at least 2–3 hours before bed, rather than taking the capsules right before lying down. A horizontal position after fatty food or oil capsules increases the likelihood of heartburn.

If you take a combined product, look carefully at whether it contains caffeine, synephrine, guarana extract, or green tea. Such products should be taken in the first half of the day: the half-life of caffeine is on average several hours and in some people significantly longer.

• Take CLA together with your main meals.
• Do not swallow the capsules right before bed if you are prone to heartburn.
• Check the label for the presence of stimulants.
• Assess sleep over several weeks, not over one night.

If sleep disturbances appeared while taking any supplement and do not go away, it is logical to take a break and see whether sleep returns to normal. Chronic insomnia is a reason to see a doctor, not to look for the «right» supplement.

Combined «night» fat burners

On the market there are so-called night fat burners, in which CLA is combined with L-carnitine, chromium, melatonin, valerian extracts, or other plant components. The positioning of «lose weight in your sleep» is a marketing device, not a scientifically grounded concept.

In such products the effect on sleep is determined primarily by sedative or hypnotic components, not by CLA. Melatonin, for example, is a medicine in some countries, and its appropriateness should be discussed with a doctor, especially with long-term use.

Another risk of combined products is hidden caffeine or other stimulants in the composition of «proprietary blends», where the amount of each component is not stated. Such blends make it difficult to assess exactly what is affecting your sleep.

The IOC consensus on dietary supplements (Maughan et al., 2018) also reminds of the risk of supplements being contaminated with foreign substances. For athletes who undergo doping control, this is an additional argument in favor of products with independent certification.

Editorial conclusions

CLA is not a stimulant and, according to the available data, does not directly worsen or improve sleep. There is practically no research in which sleep was the main outcome.

The real practical connection lies in gastrointestinal tolerability: large oil capsules before bed can cause discomfort and heartburn. This is easy to avoid by taking the supplement together with food earlier in the evening.

If sleep worsened while taking a «CLA product», first of all check its composition for caffeine and other stimulants.

We also recommend familiarizing yourself with our materials «CLA during a bulk: does it make sense», «How to choose a quality CLA: what to look for on the label», and «Chromium picolinate and sleep».

References

1. Gaullier JM, Halse J, Høye K, et al. Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans. Am J Clin Nutr. 2004;79(6):1118–1125.
2. 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.
3. 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.
4. Onakpoya IJ, Posadzki PP, Watson LK, et al. 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.
5. Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.
6. Kerksick CM, Wilborn CD, Roberts MD, et al. ISSN exercise & sports nutrition review update: research & recommendations. J Int Soc Sports Nutr. 2018;15(1):38.