Writing in Nutrition Research, the researchers also note that supplementation with CLA did not impact levels of parathyroid hormone (PTH), a marker of bone resorption (weakening).
“This is the first study to demonstrate a relationship between long-term CLA status (based on diet) and body composition assessments in adult men,” wrote researchers from McGill University in Canada, and the University of Sydney in Australia.
“This study is also the first to assess the effects of CLA on PTH in healthy men,” they added. “c9, t11 CLA did not appear to significantly affect intact or bioactive PTH during a 16-week supplementation.
“All men had low normal healthy concentrations of bioactive PTH ranging from 7.2 to 34.0 pg/mL throughout the study, which may have diminished our ability to document further reduction after CLA supplementation.”
CLA is a fatty acid naturally present in ruminant meat and dairy products. Due to changes in the Western diet, average intake of CLA has fallen; if the fat is removed from a dairy product to make a low fat version that will be acceptable to consumers, CLA is removed along with it.
The ingredient is most often found as a mixture of isomers: cis-9, trans-11 and trans-10, cis-12.
Commenting on the results of the new study, Dr Hiskias Keizer from Stepan Lipid Nutrition told this website: “Realistically CLA cannot be connected to bone mineral density from this research.
“It is difficult for us to find strong conclusions from this paper on CLA and bone health for a number of reasons. The paper is on bone health, and in related to the 9,11 CLA isomer, it draws conclusions for 9,11 CLA which are likely to be wrong and which are not consistent with everything else we know about the effects of the 9,11 and 10,12 isomers.
Dr Keizer noted that the paper is written to suggest that the bone health results are from 9,1 CLA, and explained that people with high 9,11 CLA in their blood probably have completely different dietary habits, and at least eat more meat and drink more milk.
“Since 9,11 CLA is just a minor component in lipid profiles, it is not very likely that CLA was causing this effect.
“It known already that body-composition is influenced by 10,12 CLA and not by 9,11 CLA. Therefore, it is not surprising that in this study supplementing of volunteers with 9,11 CLA did not affect body composition.”
“In their discussion the authors do not appear to realize that 9,11 CLA does not have any body composition effects, yet they discuss effects of CLA (almost) regardless of the isomeric composition, making the discussion not scientifically sound.
“It may be that some studies suggest that bone mineral effects are more likely to be caused by the 10,12 isomer, while others indicate that the 9,11 CLA isomer could be responsible. The authors chose to work with one of the bioactive CLA isomers only, but a more thorough discussion based on science should include the other isomer specific effects.”
The scientists performed two studies: The first was an observational study analyzing for an association between blood levels of CLA and bone mineral density, and the second was an intervention study investigating the effects of CLA supplements on PTH levels.
Results from the first indicated that higher CLA levels in red blood cells were associated higher whole body bone mineral density, higher lean body mass, lower BMIs and lower fat mass, compared with people with lower levels.
However, when CLA supplements (1.5 g c9, t11 CLA or 3.0 g c9, t11 CLA, provided by Lipid Nutrition) were taken for 16 weeks, no effects on PTH levels were observed.
Other clinical trials using CLA and calcium have observed PTH decreases of up to 8% and so the researchers postulated a CLA-calcium combination “could potentially decrease PTH given elevated physiological concentrations”.
The researchers were not to be dissuaded from a potential benefit for CLA for men with elevated PTH levels, and said that, based on other studies where PTH was reduced by CLA in humans and animals, “a larger-scale study of the effects of CLA in older individuals with elevated PTH or in patients with secondary hyperparathyroidism or PKD” should be considered.
Source: Nutrition Research
Published online ahead of print, doi: 10.1016/j.nutres.2012.08.006
“Conjugated linoleic acid is related to bone mineral density but does not affect parathyroid hormone in men”
Authors: J.R. DeGuire, N. Makarem, C.A. Vanstone, S. Morin, G. Duque, H.A. Weiler