In 30 seconds
- CLA is well tolerated: in a 6-month trial with 3.2 g a day no adverse effects were seen, and in a one-year trial they were as frequent as with placebo.
- What has been described is mainly digestive discomfort: abdominal pain, constipation, diarrhoea or loose stools.
- EFSA considers 3-3.5 g of CLA a day safe for 6 months.
- If you are pregnant or breastfeeding, have diabetes or take medication, check with your doctor first.
CLA is well tolerated at the doses used in studies. What has been described is mainly digestive discomfort, such as constipation, diarrhoea or loose stools 6. EFSA considers 3-3.5 g a day for 6 months safe 2, and only some people need to check with their doctor first.
The trials in people
From 6 months to 2 years taking CLA
Is CLA safe?
To begin with, CLA is not a foreign substance in your diet. It occurs naturally in dairy products and beef 1. Supplements concentrate it from plant oils, such as safflower oil.
Trials in people back this up:
- 6 months: 40 adults aged 18 to 44 took 3.2 g of CLA a day or placebo. No adverse effects were seen 3.
- Their blood tests, unchanged: insulin sensitivity, blood lipids and liver and inflammation markers stayed the same 3.
- 1 year: in 180 overweight adults, men and women, adverse effects were no different from those in the placebo group 4.
- 2 years: 134 of those participants continued for a second year with 3.4 g a day. The authors concluded that CLA was well tolerated, and adverse effects were less frequent than in the first year 5.
Possible side effects
According to the US NIH Office of Dietary Supplements, CLA is well tolerated. The most frequent effects are digestive: abdominal discomfort or pain, constipation, diarrhoea, loose stools, nausea and indigestion 1.
In the trials lasting 6 months or longer, the effects described were constipation, diarrhoea and loose stools 6.
| Effect | When it is described | What to do |
|---|---|---|
| Abdominal discomfort or pain | Among the most frequent effects | Always take it with a meal |
| Constipation, diarrhoea or loose stools | In trials of 6 months or longer | Spread the 3 softgels across your meals |
| Nausea or a heavy feeling after eating | Among the effects described | Stay within the dose on the label |
| Discomfort that does not go away | Uncommon | Stop taking it and mention it to your doctor |
Sources: US NIH Office of Dietary Supplements and Onakpoya et al., 2012.
Three softgels a day of an 80% CLA provide 2,400 mg of CLA, below the 3-3.5 g a day that EFSA assessed 2. The golden rule is simple: follow the dose on the label and take it with food.
CLA a day
Your dose, compared with EFSA's reference
How long can you take it for?
The European Food Safety Authority (EFSA) considers 3-3.5 g of CLA a day safe for up to 6 months. Its safety assessment covers that period 2.
In practice, this fits a fat-loss phase, which rarely lasts longer. If you want to continue for more than 6 months, talk to your doctor.
Who should check first
For some people, it is best to ask first. Check with your doctor if:
- You are pregnant or breastfeeding. In its assessment as a novel food in the EU, the proposed labelling already advised against taking it at these stages, and against giving it to children under 5 7.
- You take medication. That same labelling asked people to check with their doctor first 7.
- You have type 2 diabetes. EFSA has not established its safety in these people 2.
It is also a supplement for adults, not for children. If any of these applies to you, a quick word with your doctor will put your mind at rest.
And in women?
It is one of the most searched questions, and the answer is reassuring. The large CLA trials included men and women. In the one-year trial, with 180 adults, adverse effects were no different from those with placebo 4.
EFSA's reference, 3-3.5 g a day for 6 months, does not distinguish between men and women 2. What does make a difference is pregnancy and breastfeeding: at those stages, check with your doctor first 7.
If you want to see what the studies carried out in women found, you will find it in CLA in women: what the studies say.
How to take it properly
- 3 softgels a day: one with breakfast, one with lunch and one with dinner. That is 2,400 mg of CLA.
- Always with food. It is a fatty acid.
- Within the dose. If you forget a softgel one day, do not take two at the next meal.
- Consistently. In the reference meta-analysis, the effect on fat grew in a linear way for up to 6 months 8.
CLA contains no caffeine or other stimulants, so you can take the softgel with dinner without thinking about your sleep. You will find the full schedule in how to take CLA. It is one of the reasons many people prefer it to fat burners made with caffeine or synephrine, which we compare in fat burners: which ones work.
Compared with placebo
What the trials with CLA found
What you can expect
Taken properly, CLA has interesting studies behind it:
- Body fat: in a meta-analysis of 18 trials, with 3.2 g a day, people lost 0.09 kg more fat per week than with placebo 8.
- At one year: in 180 overweight adults, fat mass ended up between 6.9 and 8.7% lower than in the placebo group 4.
- In the long term: in trials of 6 months or longer, 1.33 kg less fat than with placebo 6.
You will find all the studies in CLA: what the studies say and the practical summary in what CLA is good for.
Frequently asked questions
Does CLA have side effects?
It can, mainly digestive ones: abdominal discomfort, constipation, diarrhoea or loose stools. In general it is well tolerated: in a 6-month trial with 3.2 g a day no adverse effects were seen.
Does CLA have side effects in women?
The large CLA trials included men and women. In the one-year trial, with 180 adults, adverse effects were no different from those with placebo. If you are pregnant or breastfeeding, check with your doctor first.
Who should not take CLA?
Check with your doctor first if you are pregnant or breastfeeding, take medication or have type 2 diabetes. It is also a supplement for adults, not for children.
How long can you take CLA for?
EFSA considers 3-3.5 g of CLA a day safe for 6 months. If you want to continue for longer, check with your doctor.
How many CLA softgels can you take a day?
As many as the label says. With an 80% CLA, 3 softgels a day, one with each main meal, provide 2,400 mg of CLA: below the 3-3.5 g a day that EFSA assessed.
Sources
- Office of Dietary Supplements, National Institutes of Health. Dietary supplements for weight loss: fact sheet for health professionals. View publication
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Statement on the safety of the «conjugated linoleic acid (CLA)-rich oils» Clarinol® and Tonalin® TG 80 as novel food ingredients. EFSA Journal. 2012;10(5):2700. View publication
- Watras AC, Buchholz AC, Close RN, Zhang Z, Schoeller DA. The role of conjugated linoleic acid in reducing body fat and preventing holiday weight gain. Int J Obes. 2007;31(3):481-487. View publication
- 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. View publication
- Gaullier JM, Halse J, Høye K, et al. Supplementation with conjugated linoleic acid for 24 months is well tolerated by and reduces body fat mass in healthy, overweight humans. J Nutr. 2005;135(4):778-784. View publication
- 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. View publication
- Food Safety Authority of Ireland. Initial assessment: Clarinol™ CLA-rich oil. 1 May 2008. View publication
- 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. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
