Updated 27 February 2013

Trans fats and weight loss

Natural trans fats contain conjugated linoleic acid (CLA) which may aid weight loss. DietDoc takes a closer look.

The public often want to know if taking a CLA supplement will aid weight loss. CLA or conjugated linoleic acid is a trans fat that occurs naturally in the fat of ruminant animals (i.e. animals that chew the cud like cows, sheep, goats and water buffalo in more exotic climes) (Dairy Nutrition, 2013). CLA supplements are also produced commercially and sold for a variety of purposes, including weight loss.

Trans fat conundrum

We have been repeatedly warned not to eat any trans fats because the so-called "industrial" trans fats that are found in hard or block margarine and processed foods that contain such fats, are regarded as even more atherogenic (“artery clogging”) and carcinogenic than saturated fats and any other type of fat that humans may ingest.

Now researchers come up with statements that "current evidence suggests ruminant trans fats are not associated with an increased risk of cardiovascular disease. In fact, emerging evidence suggests a beneficial effect of specific ruminant trans fatty acids on cardiovascular health". (Dairy Nutrition, 2013).

So although it may be difficult to differentiate, we need to keep in mind that two types of trans fats have been identified, namely "industrial" potentially harmful trans fats, and "natural ruminant" potentially beneficial trans fats. The latter group of trans fats includes CLA which may have weight loss properties.

Two types of CLA

Just to complicate matters even further, it is also a fact that there is a difference between the CLA in foods derived from ruminants (e.g. full-cream milk, dairy products, cheese, meat) and the CLA that is available in supplement form! According to Pfeuffer and her coworkers (2011), the CLA found in dairy foods contains cis9,trans11-18:2, whereas industrially produced CLA preparations (as may be used in slimming supplements) contain cis9,trans11 and trans10,cis12. It has been suggested that naturally occurring ruminant CLA may be more beneficial in regard to a wide variety of conditions than commercially produced CLA because of this difference in the chemical composition.

Chinese study

However, a recently published Chinese study found that commercially produced CLA (which contained cis-9,trans-11 and trans10,cis-12 CLA), reduced body weight, BMI, subcutaneous fat mass and waist-to-hip ratio in the CLA-treated subjects when compared to controls. The differences in fat markers were significant, particularly in female test subjects (Chen et al, 2012). It is, therefore, possible that commercially manufactured CLA (which has a different chemical configuration to that of CLA produced by ruminant animals), can also produce weight loss effects.

In this study, Chen and coauthors (2012), randomly treated 63 subjects with BMIs of 24 to 35 kg/m2 (overweight to obese) with a dose of 1.7 gram twice a day of the above mentioned commercial CLA supplement for 12 weeks (CLA treatment group = 30 subjects). The control group of 33 overweight to obese subjects were given placebo (dummy treatment) twice a day for 12 weeks. The authors concluded that supplementation with CLA for 3 months in overweight to obese Chinese individuals led to weight loss and a reduction in obesity markers, without any serious negative effects.

CLA in dairy products vs CLA supplements

Researchers at the Northern Ireland Centre for Food and Health, also state that in relation to CLA "...the only evidence that is broadly consistent is an effect on body fat and weight reduction". (McCrorie et al, 2011).  However, they point out that a previous review of studies relating to the weight loss effect of CLA found that the use of 3.2 g of CLA per day in human subjects produced a reduction of about 0,09 kg per week. In other words, these subjects lost 90 gram in weight per week which I suspect would fall far short of most slimmer’s expectations. If the majority of people who try to lose weight get impatient and frustrated when they lose half a kg (500g) per week, then losing only 90 g per week or 5 times less would lead to extreme frustration.

McCrorie and her team (2011) also caution that synthetic CLA has been suspected of being pro-diabetic in individuals who are already at risk of developing diabetes.

Heart Health and CLA

Animal studies have shown positive effects of CLA in relation to heart health, whereas some human studies have indicated that commercial CLA supplements may increase total cholesterol, triglycerides, LDL lipoprotein and fasting blood glucose levels (Chen et al, 2012).

In a German study conducted with 85 overweight men (aged between 45 and 68 years) with  BMIs between 25 and 35 kg/m2, the subjects were either randomly assigned to receive 4,5 g/day of CLA or safflower oil, heated safflower oil, or olive oil for 4 weeks. The function of the endothelium or lining of the arteries was determined using sophisticated tests (Pfeuffer et al, 2011). 

The authors found that CLA did not impair the function of the artery linings, and that it resulted in a moderate decrease in body weight of 1,1 kg on average over 4 weeks (i.e. 0,275 g per week) (Pfeuffer et al, 2011).


Our knowledge of commercially produced CLA is still incomplete. So far, researchers have not been able to duplicate the positive weight loss or other effects previously obtained with experimental animals, in human studies. To date, it seems evident that humans may lose some weight (between 90 to 275g per week) if they take a commercial CLA supplement, but because there are some indications that the use of commercial CLA may have pro-diabetic effects, it may be prudent not to use CLA for purposes of weight loss just yet. It is probably better to err on the side of caution and to wait until we have more human data relating to the effects of commercial CLA supplements on weight loss and health, before using CLA as a weight loss supplement.

(References: Chen SC et al (2012). Effect of conjugated linoleic acid supplementation on weight loss and body fat composition in a Chinese population. Nutrition, Vol 28(5)P559-65; Dairy Nutrition, (2013). The impact of CLA & The facts on natural trans fats and cardiovascular disease. what-is-cla ; McCrorie TA et al (2011). Human health effects of conjugated linoleic acid from milk and supplements. Nutrition Research Reviews, Vol 24(2):206-27; Pfeuffer M et al (2011). CLA does not impair endothelial function and decreases body weight as compared with safflower oil in overweight and obese male subjects. Journal of the American College of Nutrition, Vol 30(1):19-28.)


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