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


Lambert EV, Goedecke JH, Bluett K, Heggie K, Claassen A, Rae DE, West S, Dugas J, Dugas L, Meltzer S, Charlton K, Mohede I. Conjugated linoleic acid vs. high-oleic acid sunflower oil: Effects on energy metabolism, glucose tolerance, blood lipids, appetite and body composition in regularly exercising individuals. Br J Nutr 2007; 97: 1,001-1,011.

PubMed ID: 17381964
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
  • The primary aim of the present study was to measure the effects of CLA administration vs. a high-oleic acid sunflower oil control, on whole body substrate oxidation at rest and during exercise, resting energy expenditure, body composition and regional adipose tissue distribution in regularly exercising individuals
  • A secondary aim was to examine the effects of CLA on blood lipid profiles, glucose homeostasis and insulin sensitivity in already exercising, normal-weight persons.
Inclusion Criteria:
  • Regularly exercising: Three or more times per week and who had been exercising at this level for more than six months 
  • Between the ages of 21 and 45
  • Weight stable (±2-3kg) for three months preceding the trial.
Exclusion Criteria:
  • Chronic illness or medication
  • Existing lipid disorders
  • Obesity (BMI >30kg/m2)
  • Diabetes
  • Hypertension
  • Women who were lactating or who were planning on becoming pregnant
  • Currently taking nutritional supplements, other than a general multi-vitamin supplement.
Description of Study Protocol:


Recruited from the fitness center of the Sports Science Institute of South Africa or a similar facility.


  • Double-blind, randomized controlled trial
  • Method of randomization was not given.

Blinding used



  • Control supplement
  • CLA supplement.

 Statistical Analysis

  • Sample size was determined using GraphPad Instat, version 2.05a. In order to be able to detect differences in body fat mass (kg) of 1.5kg with a standard deviation of 1.75 (kg) and differences in body fat of 1.5% with a standard deviation of 2.0%, at an alpha level of 0.05, and with 80% power, a sample of size of between 14 and 18 per group was required. The sample size takes into consideration for multiple effects (gender and treatment). In addition, to detect differences in RMR of 0.6MJ per day with a standard deviation of 0.7MJ per day, a sample size of fourteen per group was required.
  • Two-factor, repeated measures of ANOVA was used to explore changes in body composition and metabolic parameters over time, between men and women, the CLA and control groups
  • Where there were significant effects attributed to gender differences, we subsequently adjusted for body composition
  • Alpha<0.05 was considered to be statistically significant.
Data Collection Summary:

Timing of Measurements

  • 12-week intervention
  • Every two weeks the subjects met with registered dietitians to report any adverse events or any changes in training, lifestyle or eating patterns, and to assess pill compliance. In addition, at each of these visits, subjects were asked to complete a visual analogue scale measuring hunger, fullness, satiety and prospective intake, prior to and for three hours following the ingestion of a standardized breakfast snack.
  • Cardio-respiratory fitness, body composition, oral glucose tolerance tests, blood lipid profiles, fasting RMR and RER and RER during exercise were taken prior to and 12 weeks after the intervention
  • Three four- day dietary records were done at baseline (week one), and weeks six and 12
  • Physical activity was measured using a seven-day physical activity recall questionnaire prior to the start of the intervention and at the end of the 12-week period
  • The visual analogue scale measures of appetite were completed every two weeks, through the 12 week intervention.

Dependent Variables

  • Body composition: Sum of seven skinfolds, weight, height, waist and hip circumferences, fan-beam DEXA
  • Appetite: Subjective motivation to eat (hunger, satiety, fullness and prospective consumption) was assessed by repeated administration of 100mm visual analogue scales prior to a test breakfast in the fasted state (10-12 hours) and then hourly for three hours following the test meal. The test breakfast comprised a 100g muffin (Muffinmate CC) and 200ml pure fruit juice (Parmalat) which were individually packaged.
  • Oral glucose tolerance: after 10- to 12-hour overnight fast; fast blood sample was drawn the subjects ingested 75g glucose dissolved in 250mL water; blood samples were drawn at 30-minute intervals for two hours for the determination of plasma glucose and NEFA concentrations; blood was drawn at 30 and 120 minutes post-glucose ingestion for determination of plasma insulin concentrations
  • Insulin sensitivity and resistance: Estimated from fasting and glucose-stimulated blood glucose and insulin concentrations, based on the homeostasis (HOMA) and the QUICKI models
  • Maximal oxygen uptake, energy expenditure and substrate utilization at rest and in response to sub-maximal exercise: All subjects tested for VO2max and peak sustained power output on an electronically braked cycle ergometer; the results of the initial maximal test were used to determine the workload that corresponded to 25% and 65% of VO2max. On another day, after a 10- to 12-hour overnight fast, subjects arrived at the laboratory, and rested in supine position for 30 minutes prior to the start of each test. Energy expenditure and substrate utilization were assessed at rest, using the canopy or ventilated hood technique, by measuring O2 uptake and CO2 production at 60-second intervals for 20 minutes or until subjects reached  steady state. From these measurements, the resting energy expenditure and RER were determined using the equations of Frayn. Following the resting measurements, sub-maximal exercise was performed by the subjects at two exercise intensities (25% and 65% of VO2max) for 15 min each on a cycle ergometer, with 15-minute seated rest separating the two bouts. During the sub-maximal exercise session, substrate oxidation was calculated based on the gas exchange measured using a breath-by-breath OxyconSigma Analyzer. 

Independent Variables

  • Control supplement: 3.9 high-oleic acid sunflower oil (HOSF) per day
  • CLA supplement: 3.9g CLA supplement (Formule Naturelle Ltd; containing Clarinol from Loders Croklaan, Lipid Nutrition); 65.0% CLA, c9t11 isomer (29.7%) and c10t12 isomer (30.9%) and also contained minimal amounts of other CLA isomers (2.9%); in addition, the capsule contained oleic acid (18:1n-9, 24.7%) and a small amount of palmitic acid, stearic acid and linoleic acid. 

Control Variables

  • Three-Factor Eating questionnaire to screen for individuals demonstrating restrained eating or high levels of dietary disinhibition
  • Three four-day dietary records
  • Subjects recorded their daily physical training and also completed a physical activity questionnaire prior to the start of the intervention and at the end of the 12-week period.
Description of Actual Data Sample:
  • Initial N: 64
    • 26 men
    • 38 women
  • Attrition (final N):
    • 62
    • One withdrew due to personal reasons and the other due to medical reasons
  • Age: 32 (SD seven) years
  • Ethnicity: Not given
  • Other relevant demographics: Not given
  • Anthropometrics pre-intervention:
    • BMI:
      • Men 22.5 (2.5)
      • Women 24.2 (2.1)
    • Sum Skinfolds (mm):
      • Men/CLA 75.2 (24.3); men/control 83.7 (30.8)
      • Women/CLA 107.0 (21.3); women/control 117.9 (25.0)
    • Percent Fat (DEXA):
      • Men/CLA 18.2 (5.4); men/control 18.3 (9.3)
      • Women/CLA 29.2 (6.7); women/control 32.4 (6.1)
    • Fat-free (DEXA) (kg):
      • Men/CLA 62.0 (5.5); men/control 60.2 (4.7)
      • Women/CLA 41.9 (4.8); women/control 40.7 (3.5)
    • VO2max:
      • Men 41.2 (6.0)
      • Women 50.8 (7.5)ml/kg per minute
    • Groups were well matched for age, mass and anthropometrical characteristics. However, there was a significant difference in dietary restraint between the males in the control and CLA groups. When included as a covariate in the analysis, dietary restraint did not alter any of the subsequent relationships.
  • Location: South Africa.
Summary of Results:

 Key Findings

  • CLA supplementation was not associated with any statistically significant changes in body mass or body composition in men or women. There were also no significant changes in regional body fat distribution in either group.
  • Resting RER and RMR, expressed in absolute (MJ per day) or relative (kJ/kg fat-free mass (FFM) per day) terms, did not change in response to CLA treatment over 12 weeks, in either men or women
  • Absolute RMR decreased with weight loss in both groups, and RER increased significantly from pre- to post-testing (P<0.001)
  • No difference in response to CLA treatment over 12 weeks in substrate utilization during sub-maximal exercise
  • CLA did alter fasting measures of appetite at any stage in either men or women
  • There were no changes in nutrient or energy intake or training frequency reported at the beginning, mid-way or at the end of the trial.

Table 1. Post-intervention body composition changes (mean (SD)).

  Men/CLA Men/Control Women/CLA Women/Control
Sum Skinfolds (mm) 76.5 (24.8) 83.3 (28.0) 96.9 (21.2) 113.8 (25.7)
Percent Fat (DEXA) 18.6 (5.7) 18.8 (8.2) 28.2 (6.4) 32.2 (6.1)
Fat-free (DEXA) (kg) 62.2 (5.8) 60.1 (4.6) 41.7 (5.2) 40.2 (3.7)

Other Findings

  • The pill compliance was above 90% in both groups: CLA 93.9 (6.5) vs. Control 95.2 (6.0)
  • The capsules were well-tolerated, with only a few subjects reporting sporadic adverse events. The adverse events reported in the CLA and control groups were headaches (6% vs. 16%). bloating (29% vs. 23%), diarrhea (48% vs. 35%), flatulence (16% vs 0%), skin irritation (13% vs 19%), and flu or cold (32% vs. 42%), respectively. Adverse events were not different between groups.
  • Plasma glucose concentrations were not different in response to an oral glucose load in either of the groups and in men and women following the 12-week intervention period
  • Mean plasma insulin concentrations (at zero, 30 and 120 minutes) were statistically lower in women taking CLA following the 12-week intervention period, compared to the control group of women (P=0.04, gender x time x treatment interaction)
  • A significant association was found between the change in mean plasma insulin concentrations over the 12-week intervention, and the change in body fat (r 0.36, P=0.032)
  • Mean serum NEFA concentrations were significantly attenuated in response to an oral glucose load after 12 weeks of supplementation in the CLA group compared to the control group (P=0.001, time x treatment interaction)
  • Insulin sensitivity, insulin resistance and the fasting glucose/insulin ratio were not significantly different between treatment or control groups, in men or women
  • Significant decreases were found in serum total cholesterol and LDL concentrations in both groups and decreases in HDL-cholesterol concentrations in women only, over the 12-week intervention (P=0.001, P=0.017 and P=0.02). However, after covarying for body composition, these differences were no longer significant, nor were there significant changes in serum triacylglycerol concentrations in response to CLA supplementation.


Author Conclusion:

Mixed-isomer CLA supplementation had a favorable effect on serum insulin and NEFA response to oral glucose in non-obese, regularly exercising women, but there were no CLA-specific effects on body composition, energy-expenditure or appetite. 

Authors stated that to their knowledge, this was the first controlled, clinical trial that demonstrated this effect in normal-weight persons who were regularly exercising.

Further human studies are recommended, in order to determine the specific mechanisms underlying these effects, in particular, the isomer-specific nature of the adaptations, and any potential adverse effects and dose-response relationships in obese or insulin-resistant individuals.

Limitation: In the current study sample, subjects were generally insulin-sensitive, and found to be at the higher range of values previously reported for non-diabetic, control populations for QUICKI and at the very low range of values for HOMA-IR. Therefore, these indices may not be as sensitive to change in the extreme ranges, and in non-diabetic, non-obese, fit individuals.

Funding Source:
Government: Medical Research Council of South Africa
Loders Croklaan; RP Scherer; Aspen Pharmacare; Technology and Human Resources for Industry Programme
Food Company:
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:

30-40% of subjects reported cold or flu which raises the question as to whether these conditions could impact lipid metabolism and utilization of the CLA, thus impacting overall results.

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? 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