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

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

The aim of this study was to measure the incorporation of the c9t11 and t10c12 CLA isomers into adipose tissue and skeletal muscle in apparently healthy, non-obese, exercising individuals supplementing with a commercially available 50:50 c9t11:t10c12 CLA preparation.

Inclusion Criteria:

Individuals who:

  • Exercise at least three times per week for six months
  • BMI <30kg/m2
  • Maintained stable weight (± 2-3kg) for three months preceding the trial
  • Not suffering from chronic illness
  • Not taking medication or nutritional supplements other than general multivitamin.
Exclusion Criteria:

Lactating women or those planning on becoming pregnant

Description of Study Protocol:


This experiment was part of a larger study, details described elsewhere


  • Two-week placebo trial
  • Baseline testing
  • 12 weeks of supplementation
  • Follow-up testing.

Blinding used

Not used


  • The 3.9g daily CLA supplements were taken each morning as four capsules, consisted primarily of the c9t11 (29.7%) and t10c12 (30.9%) isomers, as well as other CLA isomers (2.9%) and oleic (18:1 n-9; 24.7%), palmitic (16:0; 3.5%), linoleic (18:2 n-6; 1.9%) and stearic (18:0; 1.3%) acid (Formule Naturelle Ltd., France, containing Clarinol TM from Loders Croklaan, Lipid Nutrition, The Netherlands). The placebo capsules contained 3.9g of high oleic acid sunflower oil.
  • Samples were taken to determine the fatty acid composition of adipose tissue and muscle triacylglycerols (TAG), and the muscle membrane phospolipids. Fasting gluteal adipose tissue biopsies were obtained prior to and after the 12-week intervention period. Biopsies of vasus lateralis muscle were taken from a sub-group (six CLA, six Placebo).

Statistical Analysis

  • Baseline characteristics of CLA and placebo groups compared using independent T-tests
  • To examine effect of supplementation on all measured variable, two-way repeated measure ANOVA was used
  • Correlations were performed using Pearson product moment test
  • Statistical significance was accepted at P<0.05
  • All results presented as mean ± SD.
Data Collection Summary:

Timing of Measurements

  • Fasting gluteal adipose tissue taken before and after the 12-week protocol
  • 12-week CLA supplementation
  • A sub-sample of participants (six CLA and six placebo) also had biopsies of vastus lateralis muscle.

Dependent Variables

  • Variable 1: Incorporation of c9t11 and t10c12 CLA isomers into adipose tissue analyzed for fatty acid composition
  • Variable 2: Incorporation of c9t11 and t10c12 CLA isomers into skeletal muscle analyzed for fatty acid composition
  • Physical activity
  • Body composition
  • Glucose/insulin parameters
  • Serum lipids.

Independent Variables

CLA (50:50 t9c11:c10t12) 3.9g supplementation

Control Variables

Dietary fats


Description of Actual Data Sample:
  • Initial N:
    • CLA=11
    • Placebo=14
  • Attrition (final N): No attrition
  • Age: 21-45
  • Ethnicity: Caucasian
  • Other relevant parameters: Dietary analysis indicated that the contributions of:
    • Saturated (CLA: 13.4±9.1%, placebo: 11.4±5.7%, P=0.570)
    • Monounsaturated (CLA: 9.4 ± 3.5%, placebo: 7.4±2.5%, P=0.094)
    • Polyunsaturated (CLA: 6.5±3.0%, placebo: 6.4±2.7%, P=0.900) fats to the diet were similar in both groups prior to the trial
  • Anthropometrics: Similar baseline body composition (Body mass, BMI, Body fat), fasting glucose and insulin levels, and insulin resistance prior to supplementation 
  • Location: South Africa.


Summary of Results:

 Key Findings

  • Adipose tissue:
    • Significantly higher levels of the t10c12 isomer (P<0.001) and Oleic acid (P=0.019) were present in adipose tissue TAG in the CLA group than in the Placebo group
    • The c9t11 isomer, linoleic acid, total saturated, monounsaturated and polyunsaturated fatty acid and all other fatty acid (data not shown) levels measured did not change over the supplementation period
  • Skeletal Muscle:
    • There was a trend for the c9t11 isomer (P=0.056) and oleic acid (P=0.055) to be incorporated into the skeletal muscle phospholipids of the CLA group
    • There was no evidence of incorporation of CLA isomers into skeletal muscle TAG
    • The t10c12 isomer was not present in the phospholipids and supplementation did not change the levels of linoleic acid, total saturated, monounsaturated or polyunsaturated fatty acids or any of the other fatty acids (data not shown) measured.

Other Findings

  • CLA supplementation did not alter body composition, glucose or insulin parameters, or the serum lipid profiles (data not shown) of the two groups
  • Dietary analysis indicated that the contributions of saturated, monounsaturated, and polyunsaturated fat remained constant during the trial (data not shown)
  • Reported physical activity energy expenditure remained constant throughout the trial for all subjects (P=0.433).
Author Conclusion:

Following supplementation, the t10c12 isomer was incorporated into adipose tissue triacylglycerol (P=0.001), and the c9t11 isomer tended to increase in skeletal muscle phospholipids (P=0.056). The fatty acid composition of adipose tissue TAG and skeletal muscle phospholipids may be altered in an isomer-specific manner with CLA supplementation in healthy, non-obese, regularly exercising individuals. The functional significance of these findings has yet to be elucidated.

Funding Source:
Loder Croklaan, Netherlands; RP Schere, UK; Aspen Pharmacare, S. Africa; Technology and Human Resources for Industry Programme, S. Africa
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:

Although the studies found differences in uptake of various CLA isomers into adipose and muscle tissue, there was no functional implication found in this study (no change in body composition or insulin sensitivity). Speculations on functionality are proposed in the discussion section. As discussed, small sample size may not have been sensitive enough to detect physiologic changes. Additionally, the author speculates that perhaps a longer trial period would have resulted in physiologic changes. 

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? Yes
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? N/A
  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? Yes
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  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? N/A
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