Peer Review History: Risk Assessment of “Other Substances” – Conjugated Linoleic Acids

The Norwegian Scientific Committee for Food Safety (Vitenskapskomiteen for mattrygghet, VKM) has, at the request of the Norwegian Food Safety Authority (Mattilsynet; NFSA), assessed the risk of “other substances” in food supplements and energy drinks sold in Norway. VKM has assessed the risk of doses given by NFSA. These risk assessments will provide NFSA with the scientific basis for regulating the addition of “other substances” to food supplements and other foods.

“Other substances” are described in the food supplement directive 2002/46/EC as substances other than vitamins or minerals that have a nutritional or physiological effect. It is added mainly to food supplements, but also to energy drinks and other foods. VKM has not in this series of risk assessments of “other substances” evaluated any potential beneficial effects from these substances, only possible adverse effects.

The present report is a risk assessment of conjugated linoleic acids (CLAs), and is based on previous risk assessments of CLAs and articles retrieved from literature searches.

According to information from the NFSA, CLAs are ingredients in food supplements sold in Norway, and NFSA has requested a risk assessment of the following doses of CLAs in food supplements: 3.0, 3.25 and 3.5 g/day. The daily intakes in Norway of CLAs range between 20 and 170 mg (MoBa 2008, version 4).

The CLAs are mostly studied in overweight and obese subjects because of their claimed effects to reduce body weight.

CLAs constitute a group of isomeric fatty acids mostly produced by bacterial fermentation in the gut. In the human diet, meat (mainly isomers c9,t11 and t10,c12) and dairy products (mainly isomer c9,t11) are main sources of CLAs. The various isomers may have different metabolic effects. In the food supplements evaluated by EFSA (EFSA, 2010 a; EFSA, 2010 b; EFSA, 2012), Clarinol® and Tonalin®, the t10,c12 and the c9,t11 isomers are present in about equal proportions. In research articles not all authors are consistent in reporting what they have studied, so in this report we sometimes do not distinguish between these isomers; hence they are referred collectively to as CLAs if it is not specified.

Most of the cited studies have tested supplemental CLAs in doses of about 3.5 g/day, but ranging from 0.7 to 6.0 g/day. In most of the randomised controlled trials (RCTs) there have been no significant differences in adverse effects between the placebo and CLA-groups.

Concerns about indications of an unfavourable effect on biomarkers of lipid- and carbohydrate metabolism in obese men with metabolic syndrome as well as unfavourable effect on antioxidant status; increased markers of oxidative stress after consumption of supplemental CLAs have been reported in previous studies. No clear dose-response effects have been found. It is concluded that supplemental CLAs may impair lipid- and carbohydrate metabolism in obese men with the metabolic syndrome.

Intake of supplemental CLAs by lactating women may reduce fat content in breastmilk, and intake of supplemental CLAs by pregnant women may reduce birth weight and –length among their offsprings.

Only one randomised controlled trial has included children (6-10 years). These children were all overweight or obese, subjects likely to have a different CLA-metabolism/-effect than normal-weight subjects. VKM considers that current data are too incomplete to evaluate any doses of CLAs for children and adolescents.

There are few long-term studies, and adverse health effects were not primary outcomes in these studies. Based on available data no conclusions can be drawn for supplemental use of CLAs longer than six months.

VKM concludes that:


    • In adults (≥18 years), the specified doses 3.0, 3.25 and 3.5 g/day CLAs in food
    • supplements are considered to be unlikely to cause adverse health effects if used for
    • up to six months.
    • CLA may cause lipid- and carbohydrate disturbances in obese men with metabolic
    • syndrome as well as in overweight/obese subjects with type 2 diabetes.
    • Use of CLA supplements in lactating and pregnant women may cause reduction in
    • milk production and in the content on milk fat and cause decreased birth weight andlength
    • in their off-springs.
    • No conclusion can be made for children and adolescents.
  • Data are insufficient to conclude regarding use of CLAs for more than six months.


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