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 effects of a supplement containing chromium picolinate (CP) and conjugated linoleic acid (CLA) on changes in body weight, body composition and indexes of metabolic and cardiovascular health in overweight and class I obese premenopausal women during a 12-week period of moderate energy restriction and exercise intervention.

Inclusion Criteria:
  • Body mass index (BMI) between 25 and 34
  • 21 to 50 years of age
  • Completion of fasting blood screening
  • Completed medical history questionnaire
  • Written approval from primary health care provider
  • Signed informed consent.
Exclusion Criteria:
  • BMI less than 25 or more than 34
  • Younger than 21 or older than 50 years of age
  • Fasting blood sample screening indicated study could put the subject at risk during the study or interfere with study completion
  • Incomplete medical history questionnaire
  • No written approval from primary health care provider
  • No signed informed consent.


Description of Study Protocol:


Recruited from communities in West Lafayette and Lafayette, IN.


Randomized, double-blind, placebo-controlled study with a two-week baseline period and a 12-week diet, exercise and supplementation intervention period. Subjects were randomly assigned to the placebo or intervention group based on the data of study qualification and were not matched on any characteristics. Each woman received dietary counseling and instruction to perform moderate exercise in addition to placebo or CP-CLA supplementation.

Blinding used



Supplementation with 400mcg CR and 1.8g CLA daily for 12 weeks.

Statistical Analysis

  • Values reported as means±SEM
  • Unpaired T tests used to assess group differences at baseline
  • Main effect of time (diet+exercise) and supplementation (CP-CLA vs. placebo) and the time by supplement interactions were assessed using two-factor repeated measures analysis of variance
  • 11 subjects per group were needed for 80% power.
Data Collection Summary:

Timing of Measurements

  • Detailed food records were kept by the subjects on three non-consecutive days during baseline and intervention week one to two and 11 to 12
  • Daily log of exercise activities kept by subjects
  • At baseline and week 12, the Stanford 3 MPH treadmill protocol was used to determine heart rate responses and maximum oxygen uptake was measured 
  • Blood pressure was recorded at rest during the exercise test at baseline and week 12
  • Fasting state nude body weight was measured using an electronic scale at baseline and week 12
  • Height was measured using a wall-mounted stadiometer at baseline
  • Whole body fat and fat-free masses were measured at baseline and week 12 using dual X-ray absorptiometry
  • Fasting-state blood samples were drawn at baseline and week 12
  • 24-hour urine collections were made on two consecutive days during baseline and intervention weeks one to two and 11 to 12.

Dependent Variables

  • Body weight
  • Body composition
  • Indexes of metabolic health
  • Indexes of cardiovascular health
  • Dietary intake.

Independent Variables

Diet changes and exercise combined with CP-CLA supplementation or placebo. 

Control Variables

  • Dietary intake
  • Aerobic fitness
  • Supplement compliance as measured by urinary chromium excretion.
Description of Actual Data Sample:

Initial N: 59 females

Attrition (final N): 35 females (64% of initial N)

Age: 36±1 year

Ethnicity: Not discussed

Other relevant demographics: None

Anthropometrics: No significant differences in body weight, fat mass or fat-free mass between the groups as baseline 

Location: West Lafayette and Lafayette, IN.


Summary of Results:

Key Findings

Body composition

  • With energy restrictions and exercise intervention, body weight and body fat decreased (P<0.05 significant effect of time) and fat-free mass was not changed in both groups 
  • No differences in responses between groups.

Metabolic and cardiovascular health indexes

  • Among all 35 subjects at baseline, zero had elevated glucose, 13 (37%) had elevated triglycerides, 11 (31%) had low HDL and zero had elevated blood pressure
  • Fasting hemoglobin A1c percentage, plasma glucose and insulin, insulin sensitivity, cholesterol, HDL, LDL, triglycerides, total cholesterol to HDL ratio and triglyceride to HDL ratio as well as diastolic and systolic blood pressures were not changed over time or differentially affected by CP-CLA supplementation.














Body weight






(time effect)

75.4±2.3 72.8±2.5



(time effect)

Fat mass






(time effect)

32±1.7 29.3±1.8



(time effect)

Fat-free mass





40.8±1.1 40.9±1.1 0.1±0.2


Other Findings

Dietary energy and nutrient intakes

At weeks one to two and weeks 11 to 12 of the intervention, dietary energy and fat intakes were lower, protein and carbohydrate intakes were not different and fiber and chromium intakes were higher in both groups with no differences between groups (P<0.05).

Aerobic fitness

  • Resting heart rate did not change over time for either group 
  • Heart rate at three miles per hour and five degree grade decreased (P<0.05).

Supplement compliance

  • Urinary excretion in the CP-CLA group increased 22-fold from baseline, with no change in excretion for the placebo 
  • Chromium excretion at mid and post was higher in the CP-CLA group than the placebo group (P<0.0001).


Author Conclusion:

Results from this study support that combined CP and CLA supplementation for 12 weeks does not influence body weight, body composition and the selected metabolic and cardiovascular health indexes in conjunction with a dietary energy restriction and exercise program. 

Funding Source:
Nutrition 21
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:

Question if the length of intervention period was adequate.

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? 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? No
  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)? 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? 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