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

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • This study evaluated the safety of 6g per day of CLA (as ClarinolTM G80) over 12 months in humans
  • [Reviewer note: This was the last phase of a three-phase trial; details on the overall study will be provided as they are pertinent to the current study.]
Inclusion Criteria:

Inclusion criteria for beginning the study at Phase I.

  • BMI between 27 and 35kg/m2
  • Age between 18 and 50
  • Weight stable
  • No serious medical or psychiatric illness
  • No interfering drugs
  • Not pregnant or lactating.

Subjects remaining in the study at the end of Phase II entered into Phase III.

Exclusion Criteria:

None listed; essentially given in inclusion criteria.

Description of Study Protocol:


Recruited from the Clinical Nutrition Center database and by local advertisement. 


  • Randomized, double-blind placebo-controlled
  • No information on randomization was given.

Blinding used

  • For the first two phases, subjects and investigators were blinded to treatment groups: Phase I Weight Loss; Phase II Weight-maintenance/weight-regain
  • Phase III: Open label study for five months to continue to assess long-term safety. All subjects received CLA during this phase.


Phase I-weight loss

  • Placebo: High oleic sunflower oil (91.2% total unsaturated fatty acids; 8.8% saturated fatty acids)
  • CLA: 6 grams per day of CLA mixed isomers (as 7.5 grams per day Clarinol, 37.3% c9, t11 and 37.6% t10, c12)
  • Subjects received six 1.25g capsules per day containing either Clarinol or placebo
  • Subjects were supplied with a primarily liquid low calorie diet (LCD) providing 13 kcal per kg of desirable body weight (subject's weight at a BMI of 22kg/m2) over 12 weeks
  • Phase I ended when subjects had lost between 10% and 20% of initial body weight or at 12 weeks, whichever came first.

Phase II-weight-maintenance/weight-regain

  • Initially, subjects were gradually reintroduced to solid food over a two-week transition period
  • They then ate a "maintenance" diet designed to preserve or extend weight loss, but many subjects had difficulty adhering to this diet, so weight regain was common
  • Subjects were prescribed a calorie intake of about 25-20 kcal per kg of body weight at a BMI of 22kg/m2 for this maintenance diet for an additional 16 weeks.

Phase III-open label safety study

  • All subjects were given 6g of CLA per day during this phase (five months) which extended the study to 12 months total
  • Subjects were instructed to continue to follow the "maintenance diet."

 Statistical Analysis

  • Data were analyzed using repeated measures ANOVA models
  • All models included treatment assignment, week and treatment-by-week interaction term as fixed effects and subject as a random effect
  • Models were fit with and without adjustment for sex
  • Analysis were performed using Proc Mixed in SAS
  • A nominal P-value of P<0.05 was regarded as statistically significant. 
Data Collection Summary:

Timing of Measurements

  • Information is given for the entire study even though some of the results are not reported in the current article. This information was deemed important as the current study is the final phase of the entire study.
  • Baseline, beginning of Phase I
  • Clinic visits every two weeks for the remainder of the trial
  • Complete lab tests, body composition by deuterium water dilution, RMR and RQ determination, and EKG were done at all major time-points (baseline, weeks 12, 28 and 52)
  • Limited lab tests (insulin, glucose, liver function) were done at weeks at two, six, 16, 22 36, and 44
  • Body composition was performed monthly
  • At every clinic visit, vital signs, weight, and body composition by BIA were recorded, the adverse event questionnaire was completed by subjects, and subjects met with a study dietician to discuss weight loss progress and adherence to the protocol
  • Food intake and exercise diaries were submitted by subjects at every clinic visit during the LCD phase and monthly thereafter.

Dependent Variables

  • Only the variables with reported data in this study are included here
  • Laboratory tests: 
    • Standard chemistry panel with electrolytes, blood urea nitrogen, creatinine, liver function tests (ALT, AST, alkaline phosphates), serum total protein and albumin, uric acid, magnesium
    • Complete blood count (CBC): Hematocrit, hemoglobin, red blood cell indices and differential
    • Serum lipid panel: Total cholesterol, triglycerides, HDL and a calculated LDL
    • Glucose and insulin
    • HOMA calculations: Fasting serum insulin (uU/ml) x fasting plasma glucose (mmol/l)/22.5
    • All lab tests performed by the Penn Medical Laboratories.

Independent Variables

  • Placebo
  • CLA.

Control Variables


Description of Actual Data Sample:
  • Initial N: Phase I: 64
  • Attrition (final N):
    • End of phase I: 50 (Placebo: 15 females, eight males; CLA: 20 females, seven males) 
    • Reasons for drop-out were given in Table 2: lost to follow-up (one CLA); too busy (three placebo; four CLA); thyroid levels (one CLA); AEs related to LCD (one CLA); AE-rash (one CLA); Could not take LCD (one placebo, one CLA); lack of commitment (one CLA); pregnant (one placebo); AE-hair loss (one placebo); AE-lump in neck (one placebo)
    • Drops-outs: baseline (three placebo; four CLA); week two (two CLA); week four (three CLA); week eight (one CLA); week 16 (one placebo); week 18 (one placebo); week 28 (one placebo); week 38 (one placebo)
    • End of phase II: 48
    • End of phase III: 46
  • Age:
    • Placebo: 41.2
    • CLA: 43.4
    • Early Drops (N=15): 36
  • Ethnicity:
    • Placebo: One Hispanic; 22 Caucasian
    • CLA: One African American; 26 Caucasian
    • Early Drops: 13 Caucasian
  • Other relevant demographics: None listed
  • Anthropometrics:
    • Body weight (kg):
      • Placebo: 91.4±12.5
      • CLA: 93.4±13.8
      • Early drops: 88.9±8.8 
    • BMI
      • Placebo: 31.4±2.3
      • CLA: 32.0±2.1
      • Early drops: 31.9±2.4
  • Location: Appears to be Clinical Nutrition Center at the University of Wisconsin, Madison.
Summary of Results:

 Key Findings

  • The elements of particular concern from a laboratory test safety standpoint were insulin, glucose, and liver function tests
  • No significant differences between groups in insulin levels at any of the time-points
  • CLA subjects had a significantly higher serum glucose level compared to placebo subjects at week two (93.1±1.5 vs. 87.2±1.6mg/dl, P<0.007), but differences were not significant at any other time-points
  • No subject with a normal baseline glucose developed glucose tolerance (at least 110mg/dl), but one CLA subject with a baseline glucose of 112mg/dl increased to 118mg/dl
  • Using HOMA as a measure of insulin resistance, there were no differences between groups at any time point throughout the study
  • There were no significant differences between groups in any of the other laboratory measures at baseline and week 12 (AST and ALT were greater in the placebo group at week 12)
  • At week 28, CLA subjects had significantly higher TG (154.7±11.4 vs. 114.9±12.3mg/dl, P=0.02) and WBC (6.6±0.3 vs. 5.5±0.3, K/ul, P=0.02), and lower HDL (53.2±2.4 vs. 62.3±2.5mg/dl, P=0.02)
  • The CLA subjects started with higher TG and WBC at baseline (both P=NS compared to placebo), and the patterns of change with diet were approximately similar. Therefore, the differences at week 28 were felt not to be clinically meaningful.
  • At week 52, CLA subjects had higher TG (150.5±11.4 vs. 118.2±12.5mg/dl, P=0.053) and pulse (66.6±1.67 vs. 61.2±1.9 beats per minute, P=0.03)
  • All other measures at weeks 28 and 32 were not significantly different
  • The control group had a significantly greater rise in HDL from weeks 12 to 28 (10.3±2.4 vs 2.1±2.1mg/dl, P=0.01), but then had a decrease from weeks 28 to 52 while the CLA group increased HDL levels during that same time (-8.3±2.4 vs. 1.5±2.1, P=0.003) 
  • No adverse even was significantly greater in the CLA group compared to the placebo group
  • There were no significant changes overall in body weight or body fat between the CLA group and placebo [data was not shown].

 Other Findings

Conversations with some of the subjects who dropped out because they were 'too busy' suggested that they had difficulties remaining on the liquid formula LCD, and two subjects dropped out specifically for this reason.


Author Conclusion:
  • The results of this study suggest that CLA as Clarinol is safe for use up to 12 months in obese humans
  • However, because CLA has been shown to decrease breast milk fat, it should not be used in pregnant and lactating women (ref Masters et al, 2002)
  • Responses of humans to CLA are different than in animals in multiple areas of physiology and biochemistry
  • Because dietary supplements on the market are highly variable in quality and even amounts of total CLA (ref Gaullier et al, 2002), the results of this study may not be applicable for all CLA products.
Funding Source:
Loders-Croklaan; Slim-Fast provided the low calorie diet formula
Food Company:
Pharmaceutical/Dietary Supplement Company:
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) No
  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)? No
  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? 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