FNCE 2023
Session 357. Providing MNT for the Pediatric Type 1 Diabetes Population: What Does the Evidence Show?
Monday, October 9, 8:30 AM - 9:30 AM

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

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

In this study, the metabolic effects of supplementation with cis-9,trans11 conjugated linoleic acid (c9,t11 CLA) were examined in abdominally obese men at high risk for cardiovascular disease. The authors hypothesized that glucose metabolism and serum lipid profiles could be improved by c9t11 CLA. The effects of supplementation on insulin sensitivity, lipid peroxidation and body composition were tested.

Inclusion Criteria:
  • Waist girth >102cm
  • BMI=27-35kg/m2
  • Triacylglycerol concentration >1.7mmol/L or HDL-cholesterol concentration < 1.1mmol/L
  • 35-65 years old
  • Men
  • Informed consent was completed by all study subjects.
Exclusion Criteria:
  • Use of antidiabetic drugs, lipid-lowering drugs, non-steroidal anti inflammatory drugs or antioxidant supplements
  • Previous diagnosis of renal disease, liver disease, diabetes or heart disease.
Description of Study Protocol:


Recruitment was through local advertisements in Uppsala, Sweden.


Men were randomly assigned to either the CLA supplement group or the placebo group. Randomization numbers were generated by the producer of the CLA and placebo preparations (Natural Lipids, Ltd). Measures of insulin sensitivity, lipid peroxidation and anthropometrics were recorded before and after a three-month supplementation period. A 12-hour fast preceded measurement of values. Additionally subjects were asked to avoid alcohol, smoking and physical activity for 48-hours prior to their clinic visit, and to maintain their usual physical activity and diet patterns during the course of the three-month study.

Blinding used

Placebo and CLA capsules appeared identical; Natural Lipids, Ltd generated blinding. 


  • Subjects received 3 grams per day (six capsules per day, approximately 1% of total energy intake) as either:
    • Placebo: olive oil, 83% triaclyglycerol or
    • c9t11 CLA, 83% triacylglycerol
  • Analysis by gas chromatography yielded specific isomer compositions of the preparations used in the study:
    • Placebo: major fatty acid content was 82.7% c9-18:1; 5.6% c9-18:2,c12; 3.6% 16:0; and 3.3%18:0
    • CLA supplement: 83.3% c9,t11 CLA; 7.3% t10,c12 CLA; 5.5% c9-18:1; 0.46% c9,c11 CLA; 0.2% c10c12 CLA; and 1.4% t9t11 + t10t12 CLA
    • The CLA supplement provided 2.5 grams per day of c9t11 CLA and approximately 0.2 grams per day of t10c12 CLA
    • Added antioxidants were not contained in the capsules
    • Capsules were prepared by Natural Lipids Ltd (Hovebygda, Norway).

Statistical Analysis

  • Shapiro-Wilk W test used to test distributions
  • Logarithmic transformation was used for variables that showed skewed distributions. Subsequently all measures were normally distributed
  • Paired T tests assessed changes within groups between baseline to 12 weeks
  • Analysis of Covariance (ANCOVA) compared changes between groups accounting for baseline values and change from baseline values for each outcome measure
  • Power calculation was performed
  • Pearson's correlation coefficient was determined from pair-wise comparisons. Partial correlation analysis for Δ values was assessed with the use of both baseline values and Δ values as covariates
  • Significance was with two-tailed P value <0.05.
Data Collection Summary:

Timing of Measurements

 Variables were measured at baseline and again after a three-month study period.

Dependent Variables

  • Insulin sensitivity: Measured by hyperinsulinemic euglycemic clamp
  • Free 8-iso-prostaglandin F: Measured by radioimmunoassay in morning urine and adjusted for creatinine values
  • 15-keto-dihydroprostaglandin F: Measured using urinary samples with a radioimmunoassay
  • sagittal abdominal diameter: Measured at L4-5level
  • Waist girth
  • Lean body mass and body fat mass: Measured by bioelectrical impedance analysis
  • Serum insulin
  • Serum cholesterol
  • LDL cholesterol
  • Serum triacylglycerols
  • VLDL cholesterol
  • HDL cholesterol
  • Free fatty acids
  • Blood glucose.

Independent Variables

Placebo vs. c9t11 CLA groups; baseline and changes from baseline values were reported for the above dependent variables.

Control Variables

  • ANCOVA was used. Adjustments were made for age and baseline values for each variable. Change in insulin sensitivity ANCOVA was also adjusted for changes in BMI, percentage body fat and serum free fatty acid concentration.
  • Compliance with supplementation was measured at 91% (by capsule count). Differences were not observed between the groups.


Description of Actual Data Sample:
  • Initial N: 25 men
  • Attrition (final N): 25 (Two subjects, one from each group, did not complete the euglycemic clamp test, thus, N=23 for insulin sensitivity)
  • Age: c9t11 CLA group: 54±5.5 years; placebo group: 56±6.0 years
  • Ethnicity: White
  • Other relevant demographics:
  • Anthropometrics: No significant differences were reported between the groups at baseline on weight, BMI, waist girth, Sagittal diameter or body composition
  • Location: Uppsala, Sweden.


Summary of Results:
  • At baseline no significant differences were observed between the two groups on anthropometrics and metabolic variables
  • No side effects of were reported. Adverse effects on liver enzymes were not observed.

Lipid metabolism

c9 t11 CLA had no significant effects on lipoproteins, free fatty or triglyceride concentrations as compared to the placebo.

Glucose metabolism

  • CLA supplementation decreased insulin sensitivity
  • Insulin sensitivity: Change from baseline significantly lower after c9t11 CLA (-0.62 ±0.72 M/I) than with placebo (0.13±1.48 M/I); (-15% difference between groups, P<0.05)
  • Impaired insulin sensitivity was abolished after adjustment for changes in 8-iso-prostaglandin F2α concentrations, but was remained significant after adjustment for changes in serum lipids, glycemia, body mass index and body fat 
  • Blood glucose: No significant differences observed between groups
  • Serum insulin: No significant differences found between groups.

Lipid peroxidation and inflammation

  • 8-iso-prostaglandin F: 50% higher excretion with CLA than with placebo (P<0.01); changes from baseline=0.10±0.08 vs. 0.004±0.07nmol/mmol creatinine respectively
  • 15-keto-dihydro-prostaglandin F: 15% higher excretion with CLA than with placebo (P<0.05); changes from baseline=0.04±0.05 vs. 0.0008±0.05nmol/mmol creatinine respectively.

Body composition

  • After adjustment for baseline values, significant differences were not found between the groups in weight, BMI, total body fat, lean body mass, sagittal diameter or waist girth
  • A significant increase was observed in body weight (1.4±1.34kg) and BMI (0.42±0.41kg/m2) from baseline to 12 weeks in the c9t11 CLA group (P<0.05).



Author Conclusion:

The study results were in contrast to the hypothesis. Supplementation with c9t11 CLA impaired insulin sensitivity and increased lipid peroxidation compared with the placebo. The author stated that the clinical relevance of these results is unknown, but metabolic changes may be proatherogenic in obese subjects. Thus, future studies are needed to determine the safety of CLA supplements.

Funding Source:
Other: Swedish Medical Research Council, Dr P Hakanson Foundation, and Swedish Society of Medicine
Reviewer Comments:

Limitations of the study as discussed by the author:

  • Small sample size
  • Dietary intake and physical activity were not assessed. It is possible that dietary habits could have affected insulin sensitivity.
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? 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)? N/A
  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