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 assess the localization of the body fat mass (BFM) reduction in overweight and moderately obese subjects during a six-month conjugated linoleic acid (CLA) supplementation
  • To determine the safety of CLA supplementation.
Inclusion Criteria:
  • 18 to 65 years of age
  • BMI 28 to 32kg/m
  • Signed informed consent.
Exclusion Criteria:
  • Less than 18 or more than 65 years of age
  • BMI less than 28 or more than 32kg/m2
  • No signed informed consent
  • Drug therapy, special diet or taking dietary substitutes for weight loss two weeks prior to the study's start
  • Consumption of CLA supplements during last three months prior to the study
  • Pregnant or lactating women
  • Type I diabetics or people with untreated type 2 diabetes
  • History of hypertension, renal, liver, pancreatic or malignant tumors
  • People with active thyroid disease or receiving thyroid hormone substitution 
  • Adrenergic agonist users
  • Known or suspected drug or alcohol abusers
  • Clinical condition rendering person unfit to participate.
Description of Study Protocol:


Recruited from two research centers.


Parallel design with two arms, double-blinded randomized and a placebo controlled. Subjects were randomly assigned to either CLA 3.4g per day or placebo of olive oil 4.5g per day via six capsules. The subjects were on an ad libitum diet with no lifestyle restrictions. 

Blinding Used

Double blinded.


Supplementation with 3.4g per day of CLA for six months.

Statistical Analysis

  • Overall F-test used to investigate comparability between groups at baseline
  • Paired T-test used to test differences between the groups from baseline to month six
  • Categorical variables using Fisher's exact test
  • Analysis of covariance performed for comparisons between treatment groups regarding change from baseline in DEXA and weight variable.


Data Collection Summary:

Timing of Measurements

  • Baseline characteristics and demographic data recorded upon entry to study
  • Weight, BMI and vital signs recorded every three months
  • Fasting blood samples taken at baseline and six months
  • Compliance measured every three months by counting the returned unused capsules
  • Adverse events recorded every three months with serious events monitored continuously
  • Diet and exercise measured at baseline and six months by participant completed diet and exercise forms covering a period of 14 consecutive days
  • Dual-energy X-ray absorptiometry weekly used to determine body composition
  • Weight obtained at baseline via digital scale at baseline, three and six months
  • Height obtained at baseline using wall-fixed Harpenden stadiometer
  • Waist and hip measurements obtained at baseline, three and six months.

Dependent Variables

  • Amount of body fat mass
  • Body mass composition
  • Localisation of decrease in body fat mass
  • Weight and BMI change
  • Waist and hip measures
  • Diabetes markers
  • Weight associated hormones
  • Blood lipid levels
  • Inflammation markers
  • Adverse events.

Independent Variables

Supplementation with 3.4g per day of CLA.

Control Variables

  • Dietary intake
  • Amount of exercise.
Description of Actual Data Sample:
  • Initial N:
    • 118 subjects were randomized
    • 105 subjects completed at least the second visit (84 females, 21 males based on 105 subjects)
  • Attrition (final N): 93 subjects
  • Age:
    • Placebo: 48.7±9.2 years
    • Intervention group: 45.8±10 years.
  • Anthropometrics: No statistical difference between groups at baseline for weight, BMI, waist size, hip size or waist-hip ratio
  • Location: Two research centers in Norway.
Summary of Results:

 Key Findings

  • 83 subjects completed the study according to protocol and defined as the PP population
  • Body composition:
    • BFM was significantly reduced by 3.4% after six months supplementation with CLA compared with placebo (change = -1.2kg, P=0.043)
    • Decreases in BFM and fat mass percentage were already significantly higher in the CLA group as compared with the placebo group after three months of supplementation (change = -0.3kg, P=0.036 and change = -0.2, P=0.04, respectively)
    • After six months of supplementation, the difference in LBM between the CLA group and the placebo group was not statistically significant; however, within group analyses revealed a significant increase in LBM in subjects supplemented with CLA
  • Localization of BFM:
    • CLA significantly reduced the leg fat mass but not the arm or abdominal fat mass compared with placebo after six months
    • Reduction of leg fat mass in the CLA group was mainly seen in women
  • Effects of CLA on weight and BMI
    • No significant difference between the groups in weight (change = -0.9kg, P=0.15) and BMI (change= -0.3, P=0.19) after six months
    • Compared with baseline, neither group had changes in body weight or BMI
    • Individuals with BMI of 30kg/m2 or more lost weight (change = -1.9, P=0.020) and their BMI decreased significantly (change = -0.6, P=0.031) after CLA intake compared with placebo
  • Effects if CLA on waist and hip measurements:
    • Higher reduction in the waist-hip ratio in the CLA group as compared with the placebo group (change = -0.01, P=0.043) after six months of supplementation
    • Compared with baseline, the CLA group had a reduction in waist size (change = -2.6cm, P<0.001), hip size (change = -1.4, P=0.009) and waist-hip ratio (change = -0.2, P=0.042) whereas there were no significant changes within the placebo group
  • Safety:
    • CLA did not alter clinically any of the following variables; ALAT, ALP, ASAT, creatinine, erythrocytes, Hb and thrombocytes
    • Significant increases in insulin C-peptide levels after six months of CLA supplementation (P=0.017)
    • In the intervention group, glucose (P<0.001) and HbA1C levels (P=0.047) decreased compared with baseline. while in the placebo group only glucose levels decreased from baseline to month six (P<0.001)
  • Adverse events:
    • Reported by 37% of all randomized subjects with similar frequencies in both study groups (P=0.85)
    • Of 58 single events, investigators considered five events related to supplementation.

Body Composition: Change After Six Months


Intervention: CLA

Change After Six Months


Change After Six Months

Difference Between the Groups

Body fat mass (percentage)



-0.1±2.2 P<0.05
Body fat mass (kg)



+0.2±2.3 P<0.05
Arm fat mass (kg) -0.3±1.2



Leg fat mass (kg)



+0.3±1.0 P<0.05
Abdominal fat mass (kg) -0.2±2.0 +0.3±1.6  
Lean body mass (kg)



Bone mineral content (kg) 0±0.1 0±0.1  

Other Findings

  • Calorie intake decreased significantly in the placebo group but not in the CLA group compared with baseline
  • Physical exercise evaluations remained unchanged between baseline and month six within both groups.


Author Conclusion:

In this study with overweight and moderately obese subjects, observations included an approximately 3.4% decrease in BFM after six months of supplementation in the intervention population. CLA seems to be safe and well tolerated. The regional reduction in fat mass is encouraging but only appropriately designed, long-term studies will unravel the potential benefits of CLA supplementation. 

Funding Source:
Lipid Nutrition, a division of Loders Croklaan
Reviewer Comments:

 Self-reported diet and exercise information.

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? No
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? No
  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? Yes
  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