It’s a conclusion that will infuriate a CLA sector that had to swallow a multiple claim rejection from the European Food Safety Authority’s (EFSA) Panel on Dietetic Products, Nutrition and Allergies (NDA) around the weight management area in October, 2010.
Leading suppliers like Cognis-BASF and Stepan Lipid Nutrition complained bitterly at the time that the NDA never assessed the claim they believed had the strongest human data – body fat reduction – while claims for body weight, lean body mass, insulin sensitivity and DNA protection and more were canned.
In assessing a body of CLA science that stretches to more than 2500 papers, the Irish researchers from the Northern Ireland Centre for Food and Health (NICHE) at the University of Ulster, noted different forms of CLA isomers that exist in food supplements (synthetic) compared to products like milk (natural) – and how this difference has contributed to the ambiguity in results.
But they backed body fat reduction as the “the only possible candidate” to win a health claim.
Wasted opportunity
Commenting on the study published in Nutrition Research Reviews, Jaap Kluifhooft, head of regulatory and scientific affairs at Stepan Lipid Nutrition in the Netherlands, welcomed the body fat conclusion, but said he remained baffled as to why the NDA never evaluated the body fat claim given it had access to the same studies featured in the current review.
With the NDA failing to clarify why that claim was not addressed, Kluifhooft said it was a shame the current review did not engage the NDA opinion.
“It is, scientifically, a missed opportunity for the authors of this publication that they only mention EFSA's October 2010 evaluation but do not further discuss it, while they only reviewed the same material available to EFSA,” Kluifhooft said.
Of the overall ambiguity in results he added: “The overall evidence from the studies examined demonstrates a lack of definitive and reproducible results, particularly in relation to the consumption of naturally enriched CLA products, as the number of published studies is low relative to the number on synthetic supplements.”
“There is lack of evidence for milk, but certainly there are clear indications for efficacy CLA supplements and/or foods enriched with CLA to a higher dose.”
Conclusions
The researchers said there was an overabundance of animal data, much of which did not translate to human subjects, typically due to dose variance.
Body fat and weight reduction delivered the most consistent results in human trials, at least with synthetically manufactured CLA used in food supplements.
“A search of the scientific literature was conducted and showed that almost all the promising research results that have emerged in relation to cancer, heart health, obesity, diabetes and bone health have been in animal models or in vitro,” they wrote.
“Most human intervention studies have utilised synthetic CLA supplements, usually a 50:50 blend of c9,t11-CLA and trans-10, cis-12-CLA (t10,c12-CLA). Of these studies, the only evidence that is broadly consistent is an effect on body fat and weight reduction.”
The data backed a 0.09kg body fat loss per week in human subjects who consumed 3.2g per day, with the effect attributed to the t10,c12-CLA isomer. The researchers said data did not show any benefits for the c9,t11-CLA isomer.
While isolating body fat reduction as, “the only possible candidate” to win CLA’s first European health claim, they pointed out some of the scientific flaws they see existing for the fatty acid.
“…given the differences in study protocols, relatively small sample sizes and other methodological issues (including measurement of dietary CLA intakes and accurate measurement of body composition), it is not surprising that there is a lack of consensus on what health claims could be applicable to CLA, either natural or synthetic products,” they wrote.
Source: Nutrition Research Reviews
Published online ahead of print: doi:10.1017/S0954422411000114
‘Human health effects of conjugated linoleic acid from milk and supplements’
Authors: T A. McCrorie, E M. Keaveney, J. M. W. Wallace, N. Binns and M. B. E. Livingstone