DFA: Conjugated Linoleic Acid (CLA) Supplementation and Intermediate Health Outcomes (2011)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the effects of two different conjugated linoleic acid (CLA) isomers at two different intakes on body composition in overweight humans.

Inclusion Criteria:
  • BMI 25 to 30kg/m2
  • Normolipemic: Mean total cholesterol <6.0mm and mean triacylglycerol <1.5mm.
Exclusion Criteria:
  • Irregular dietary habits
  • Diastolic blood pressure >85mm Hg or systolic blood pressure >150 mm Hg
  • Unstable body weight or attempts to lower weight during the past three months
  • Presence of proteinuria or glucosuria
  • Use of medication, a diet or a clinical condition know to affect lipid or glucose metabolism
  • Drug or alcohol abuse
  • History of coronary heart disease or malignancy less than five years ago
  • Positive serology for human immunodeficiency virus or hepatitis.
Description of Study Protocol:


Recruited through announcements in local newspapers.


  • Randomized, double-blind, placebo-controlled trial carried out at the same time at two different centers
  • Volunteers were randomly allocated to one of the five groups, stratified for center, gender and BMI.

Blinding used



  • Run-in period of six weeks: All subjects consumed daily a drinkable dairy product providing 3g of high oleic sunflower oil (placebo)
  • Study duration: 18 weeks
  • Placebo: Drinkable dairy product with 3g of high oleic sunflower oil
  • Low-c9t11: Drinkable dairy product with 1.5g of purified c9t11-CLA plus 1.5g high oleic sunflower oil
  • High-c9t11: Drinkable dairy product with 3g of purified c9t11-CLA
  • Low-t10c12: Drinkable dairy product with 1.5g of purified t10c12-CLA plus 1.5g of high oleic sunflower oil
  • High-10c12: Drinkable dairy product with 3g of purified t10c12-CLA  
  • The two CLA isomers were given as a triacylglycerol and were produced by Natural Lipids LTD (Hovdebygda, Norway).

Statistical Analysis

  • Before the start of the study, it was calculated that 16 subjects in each group were needed to reach a power of 80% to detect a difference in fat mass of 2kg (or 9%) between two treatments with an alpha of 5%. A 9% fat reduction is clinically relevant according to the 1997 WHO "Consultation on Obesity," which advises weight losses in the range of 5% to 15%.
  • The responses to treatment were calculated for each subject as the change between values obtained at the end of the run-in period and values at the end of the intervention period
  • Differences among the five groups were tested by ANOVA, including center and gender as factors
  • Repeated measures ANOVA, including week 14 values, were used to look for possible treatment x time interactions, but results were comparable and, therefore, are not presented
  • Results were analyzed according to intention-to-treat (ITT) and per protocol (PP) analyses
  • Results of 84 subjects could be used for the ITT analysis because six subjects had already withdrawn during the run-in period before the first measurements
  • The PP analysis was performed on 81 subjects because results of an additional three subjects could not be used
  • When necessary, missing data were estimated with the last observation carried forward method
  • Because the results of ITT and PP analyses were comparable, only the results of the PP analysis were shown.  
Data Collection Summary:

Timing of Measurements

  • Subjects attended the study center at least every second week to collect the experimental products or for measurements
  • At each visit, subjects were weighed after an overnight fast
  • At weeks zero, four, nine, 14, 19 and 24, waist and hip circumference were measured
  • At week four (run-in period) and at weeks 14 and 24 (intervention period), body composition was measured by DXA
  • At weeks zero, four, nine, 14, 19, and 24, whole-body bioelectrical impedance analysis (BIA) was used to estimate body composition
  • Dietary intake was recorded during week four of the run-in period and in weeks 14 and 24 of the intervention period. The data were coded and analyzed by a dietitian using computerized nutrient databases, which were specific for each country.
  • Fasting blood samples were taken at the end of the run-in period and in weeks nine, 14, 19, 23 and 24 during the intervention period.
  • Liver size (Clermont-Ferrand only) was determined by ultrasound at weeks nine and 14.

Dependent Variables

  • Body composition, body fat mass and lean body mass by DXA (Hologic QDR 4500A). The same type of apparatus, which was cross-calibrated before the study using appropriate phantoms, was used at the two centers.
  • Whole-body bioelectrical impedance analysis (BIA) was used to estimate body composition with a multifrequency bioelectrical impedance apparatus (Analycor)
  • Dietary intake: Food intake was recorded for five consecutive days, including three week days and two weekend days.

Independent Variables

  • Placebo
  • Low c9t11
  • High c9t11
  • Low t10c12
  • High t10c12.

Control Variables

  • The subjects were requested not to change their usual diets, level of physical exercise, smoking habits or use of alcohol during the study
  • Subjects recorded in diaries any signs of illness or any experienced side effects
  • Unused bottles of product were returned to verify compliance
  • The fatty acid composition of plasma phospholipids was monitored in the samples obtained at the end of each period to check the dietary compliance. [reviewer note: the authors give information on blood samples and analyses, but the results are not reported in this article] 
Description of Actual Data Sample:
  • Initial N: 90
    • Men 45
    • Women 45
  • Attrition (final N):
    • Six subjects withdrew during the run-in period before the first measurements
    • One woman from the low-t10c12 group (increased concentrations of gamma-glutamyltransferase and alanine aminotransferase [three and two times the upper limit]) and one woman from the high-t10c12 group dropped out at week 13 (menstrual complaints)
    • One woman from the low-t10c12 group was excluded because she had undetectable levels of t10c12 CLA during the intervention period, indicating non-compliance
    • 82 subjects completed the study
  • Age: Means ranged from 47.5 to 49.9 years
  • Ethnicity: Not given
  • Other relevant demographics: The five treatment groups were not significantly different with respect to sex ratio and age
  • Anthropometrics:
    • At the end of the run in period, weight and BMI, fat and lean body mass, and daily energy intake were not significantly different among the treatment groups 
    • Please see Table 1 of results for baseline variables
  • Location: Clermont-Ferrand, France and Maastricht, The Netherlands.


Summary of Results:

 Key Findings

  • CLA supplementation was well tolerated
  • No treatment effects were found on changes in concentrations of insulin (P=0.534) and glucose (P=0.575). [data was not presented in this article except for changes that were mentioned in the text]
  • No significant changes among the five treatment groups in weight, BMI, and the waist-to-hip ratio
  • Irrespective of the dose, consumption for 18 weeks of either c9t11-CLA or t10c12-CLA did not significantly change the percentage of body fat (P=0.564), body fat mass (P=0.444), or lean body mass (P=0.136), as measured by DXA. Body composition, as measured with BIA, also did not reveal any significant treatment effects [data was not shown].
  • Daily energy intake was not significantly altered during the study (results shown in Table 3 of the article).

Table 1. BMI of subjects at the end of the run-in and intervention periods.

  Run-in period Intervention period Change 95% CI
Placebo (N=15)





Low-c9t11 (N=18)


27.7± 1.6 

-0.1± 0.7  

-0.7; 0.5  

High-c9t11 (N=18)


27.1± 1.6 

-0.6±1.0  -1.2; 0.0 

Low-t10c12 (N=15)

28.4±2.1  28.3±2.7  -0.2±0.9   -0.7; 0.4 
High-t10c12 (N=15) 27.1±1.3  26.7±1.0  -0.4±0.8  -1.0; 0.2 

 Other Findings

  • Figure 1 of the article shows the range of the percentage of CLA detected in plasma phospholipids at the end of the intervention period for each group. Increases were observed in the CLA groups as would be expected.
  • No center or gender effect was detected for any of the parameters
  • Liver echography did not suggest that liver ultrastructure or morphology had changed during the study in any of the five groups. There were also no indications of hepatic lipodystrophy.
Author Conclusion:
  • Human studies on the effects of CLA on body composition, for which there is no clear explanation, are not consistent
  • Our results were not in favor of a health claim for products specifically enriched with the c9t11 isomer or the t10c12-CLA isomer to reduce body fat mass in moderately overweight men and women.
Funding Source:
Government: The European Commission
Reviewer Comments:
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes