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 compare the effects of conjugated linoleic acid (CLA) and safflower oil (SAF) on changes in body weight, body composition and adipose distribution among obese post-menopausal women with type 2 diabetes (T2DM).

Inclusion Criteria:
  • Female
  • 70 years or more of age
  • Post-menopausal (absence of menses for one year or more)
  • Obese (BMI higher than 30kg/m2)
  • HbA1c 6.5% or higher and less than or equal to 14%
  • Normal hepatic enzyme activity.
Exclusion Criteria:

Tobacco use, renal or liver disease, malignant tumors, impaired cognitive function, insulin or hormone replacement therapies or placement of a pacemaker or defibrillator.

Description of Study Protocol:


Subjects were recruited from the Columbus, Ohio area over a 2.9-year period.


  • After obtaining written consent, subjects reported to the Clinical Research Center (CRC) at the Ohio State University for a screening visit to document and assess demographic information, medical history, HbA1c, hepatic enzyme concentrations, height and weight to determine BMI, cognitive function with the use of an Orientation-Memory-Concentration test and willingness to comply with the study protocol
  • Eligible subjects were randomly assigned in block fashion to two groups based on their BMI and HbA1c concentrations at screening
  • All subjects received CLA and SAF treatments in the crossover design. Subjects reported to the CRC in the early morning (before 1,000) to control for diurnal variations in hormone concentrations. Subjects fasted overnight for a minimum of 10 hours before each study visit and were asked to abstain from taking their prescribed diabetes medications and treatment capsules the morning of each study visit. The initial diet period (diet period one) was 16 weeks in  duration, followed by a four-week washout period and a second 16-week period (diet period two). A four-week washout period is typical of feeding trials with fatty acid supplementation.

Blinding Used

Subjects were assigned to a treatment order and allocated dietary supplements that were in coded and numbered containers.


  • Subjects consumed eight dietary oil capsules daily, with instructions to take two capsules with each meal and two capsules at night for a total of 8.0g dietary oil daily. Each CLA capsule contained 1.0g CLA-80 oil. The CLA treatment capsules provided 6.4g CLA isomers and 1.6g oil composed primarily of oleic and palmitic acids per day.
  • Each SAF capsule contained 1.0g SAF. The fatty acid composition of oils were periodically analyzed for composition throughout the duration of the study (every six months) and did not change
  • SAF contained 5.8% of 16:0 (palmitic acid), 2.0% of 18:0 (stearic acid). 12.0% of 18.1n-9 (oleic acid), 78.4% of 18.2n-6(linoleic acid)
  • CLA contained 1.5% of 16:0 (palmitic acid), 1.6% of 18:0 (stearic acid), 13.1% of 18.1n-9 (oleic acid), 41.6% of c9t11-CLA and 40.4% of t10c12-CLA
  • Dual-energy X-ray absorptiometry (DEXA) was used to determine body composition
  • Height was measured to the nearest 0.1cm with use of calibrated, wall-mounted stadiometer at screening visit
  • Weight was assessed with a calibrated digital scale at each study visit and recorded to nearest 0.1kg
  • Sagittal abdominal diameter (SAD) was measured as a surrogate marker of visceral adiposity. Measurements were recorded to the nearest 0.1cm at the level of the iliac crest.
  • Fasting blood samples were analyzed at each study visit for glucose, insulin, leptin, adiponectin, serum concentrations of alanine transaminase (AST), aspartate transaminase (AST) and serum fatty acids. The homeostasis model assessment for insulin resistance (HOMA-IR) was used as a proxy measurement of insulin sensitivity.
  • Diet and activity records were kept for three consecutive days (two weekdays and one weekend day) for four occasions during the study period. Data were analyzed for energy, distribution of macronutrients and fatty acids. For physical activity, subjects recorded all occupational and leisure activity in 15-minute increments. Physical activity was calculated according to established energy expenditure to estimate daily average energy cost of physical activity and metabolic equivalents per day.

Statistical Analysis

  • A mixed model design including the effects of week and treatment and interactions between week and treatment was used to fit the data from week zero to week 36
  • PROC MIXED procedure (SAS 9.1) was used to conduct the analysis
  • Measurements from each subject were treated as repeated measures, taking into account that measurements from the same subject were correlated
  • Compound symmetry variance-covariance structure was used to estimate the error variance and covariance among weeks for each subject to account for correlation within subjects
  • Orthogonal contrasts are used in the mixed model to evaluate change of BMI over time
  • All data are reported at a 5% level of significance
  • Data were not subjected to intent-to-treat analysis.


Data Collection Summary:

Timing of Measurements

  • A screening visit documented and assessed demographic information, medical history, HbA1c, hepatic enzyme concentrations, height and weight, cognitive function with the Orientation-Memory-Concentration test and willingness to comply to the protocol
  • Initial diet period (diet period one) was 16 weeks in duration, followed by a four-week washout period and a second 16-week diet period (diet period two)
  • Subjects were seen monthly at the Clinical Research Center
  • Weight was recorded at the initial visit and at monthly intervals
  • Body composition, waist and hip circumferences, skinfolds, SAD and biochemical indices were measured at the beginning and end of each diet period
  • Diet and activity records were assessed at the beginning and end of each diet period.

Dependent Variables

  • BMI (kg/m2)
  • Adipose tissue (g)
  • Trunk adipose tissue (g)
  • Lean tissue (g)
  • Waist circumference (cm)
  • Waist-hip ratio
  • Hip circumference (cm)
  • Sagittal abdominal diameter (SAD)
  • Triceps skinfold thickness (mm)
  • Subscapular skinfold thickness (mm)
  • Fasting glucose (mg per dL)
  • Fasting insulin (μU per ml)
  • Leptin (ng per ml)
  • Adiponectin (mcg per ml)
  • Alanine aminotransferase (U per L)
  • Aspartate aminotransferase (U per L)
  • Energy (kcal)
  • Carbohydrate (g)
  • Protein (g)
  • Fat (g)
  • PUFA (g)
  • Linoleic acid (g)
  • MUFA (g)
  • SFA (g)
  • Activity (Met ea).

Independent Variables

  • CLA treatment
  • SAF treatment.

Control Variables

A four-week washout period between diet periods.


Description of Actual Data Sample:
  • Initial N: 55 females
  • Attrition (final N): 35 females
  • Age: 60.1±7.9 years
  • Ethnicity: Seven African Americans, 26 White, one American Indian, one Asian
  • Other relevant demographics:
    • Time since diagnosis of diabetes: 9.71±6.24 years
    • Medication users:
      • Sulfonylureas: 23
      • Biguanides: 19
      • Thiazolidinediones: 13
      • Incretin mimetic: Zero
      • α-Glucosidase inhibitor: One
      • Combination therapy: Five
  • Anthropometrics: No differences were observed for age, ethnicity, BMI, duration of diabetes, and HbA1c between groups at baseline
  • Location: Columbus, Ohio.
Summary of Results:

Key Findings

  • A significant decrease in BMI was observed over the course of both diet periods with CLA supplementation; however, supplementation with SAF did not alter BMI
  • Total adipose mass measured by DEXA was significantly decreased by CLA supplementation; SAF had no effect on total adipose mass but was significantly related to reduced trunk adipose mass and increased lean tissue mass
  • Neither SAF nor CLA supplementation significantly altered waist circumference, waist-hip ratio, SAD or skinfold thickness measurements during the study
  • CLA had no significant effect on fasting glucose or insulin
  • SAF significantly decreased fasting glucose
  • HOMA-IR analyses showed a significant improvement of insulin sensitivity with SAF supplementation
  • Supplementation with CLA had no effect on change of the adipolines adiponectin or leptin. Supplementation with SAF significantly increased adiponectin but did not alter leptin concentrations.
  • No significant differences were observed between the groups for food sources of energy or for intakes of total fat, carbohydrate and protein; saturated fat; polyunsaturated fatty acids, linoleic acid; or monounsaturated fatty acids
  • Physical activity was unchanged throughout the course of the study.

Differential Effects of Conjugated Linoleic Acid (CLA) and Safflower Oil (SAF) on Total and Central Adipose Mass and Lean Mass1

  Diet Period One Diet Period Two P for Trend P for Comparison of Treatments
  Baseline (Week Zero) Δ Weeks Zero to 16


(Week 20)

Δ Weeks 20 to 36    
Body weight (kg           0.032 
 SAF 99.16±3.29  -0.11±0.55  97.18±4.14  0.90±0.79  0.415   
 CLA 98.86±4.13  -1.25±0.71  98.78±3.30  -0.86±0.59  0.024   


 SAF 36.3±1.2  0.1±0.2  36.4±1.4  0.5±0.2  0.054   
 CLA 37.1±1.4  -0.5±0.2  36.4±1.2  -0.4±0.2  0.002   
Adipose tissue (g           0.074 
 SAF 42,994±2,272  80±667  43,203±2,877  135±906  0.849   
 CLA 44,656±2,872  -1,076±849  42,150±2,281  -1,591±721  0.019   
Trunk adipose   tissue (g)            0.039 
 SAF 24,391±1,227  -1,203± 852  25,680±1,674  -1,943±1,267  0.042   
 CLA 25,506±1,655  1,075±1,184  23,587±1,267  314±942  0.361   
Lean tissue (g)            0.193 
 SAF 45,149±1,615  1,402±594  46,390±2,046  654±808  0.043   
 CLA 46,489±2,040  -412±756  46,513±1,625  599±642  0.851   
Waist circumference (cm           0.904 
 SAF 111.3±2.3 -1.0±0.7 110.8±2.9  1.0±1.0  0.949  
 CLA 112.0±2.9  -0.7±0.9  110.1±2.3  0.6±0.7  0.915   
Waist:hip ratio            0.190 
 SAF 0.91±0.01   0.00±0.00  0.92±0.02  -0.01±0.01  0.874   
 CLA 0.90±0.02  0.01±0.01  0.91±0.01  0.02±0.01  0.084   
Sagittal abdominal diameter (cm           0.449 
 SAF 27.3±0.6  0.1±0.4  27.6±0.9  0.7±0.5  0.239   
 CLA 27.7±0.8  0.3±0.5  27.0±0.7  -0.2±0.4  0.900   
Triceps skinfold thickness (mm           0.629 
 SAF 41.7±1.8  0.2±1.0  40.8±2.3  0.8±1.4  0.550   
 CLA 41.3±2.2  -0.6±1.2  41.7±1.8  0.5±1.0 0.940   
Subscapular skinfold thickness (mm)            0.184
 SAF 45.9±1.7  -3.5±1.2  43.2±2.3  1.5±1.8 0.366   
 CLA 43.1±2.2  43.1±2.2  42.1±1.8  1.4±1.4  0.328   

1 All values are means ± SEMs.

Effect of Dietary Oils on Serum Metabolites and Adipokines1 

  Diet Period One Diet Period Two P for Trend
P for Comparison of Treatments
  Baseline (Week Zero) Δ Weeks Zero to 16 Baseline (Week 20) Δ Weeks 20 to 36
Fasting glucose (mg per dL)           0.011
 SAF 148±8 -19±8 159±11 -11±11 0.034  
 CLA 145±10 5±10 138±9 11±9 0.137  
Fasting insulin (μU per ml)           0.462
 SAF 19.9±2.1 -1.7±1.8 13.3±2.8 -1.1±2.6 0.186  
 CLA 15.4±2.6 -1.1±2.3 17.8±2.2 1.4±2.0 0.763  
HOMA-IR           0.050
 SAF 7.1±0.9 -1.3±0.8 5.3±1.2 -0.8±1.2 0.027  
 CLA 5.4±1.1 0.1±1.0 6.2±1.0     1.3±0.9 0.592  
Leptin (ng per ml)           0.053
 SFA 30±4 1±1 27±5 3±2 0.134  
 CLA 29±5 0±2 31±4 -2±1 0.215  
Adiponectin (ng per ml)           0.059
 SAF 7.3±1.1 0.8±0.6 7.9±1.3 2.4±0.8 0.005  
 CLA 9.5±1.3 -0.3±0.8 8.3±1.1 0.8±0.6 0.878  
Alanine aminotransferase (U per L)           0.059
 SAF 28.6±1.6 -2.2±1.4 25.1±2.1 -2.4±2.0 0.063  
 CLA 25.2±1.9 -1.1±1.8 24.8±1.7   3.0±1.6 0.430  
Aspartate aminotansferase (U per L)           0.034
 SAF 31.4±2.0 -4.5±2.0 27.2±2.7 -2.5±2.8 0.043  
 CLA 28.2±2.4 -1.7±2.5 26.8±2.1 4.8±2.1 0.347  

1 All values are means ± SEMs.

Diet and Physical Activity1

  Diet Period One Diet Period Two P for Trend P for Comparison of Treatments
  Baseline (Week Zero) Δ Weeks Zero to 16 Baseline (Week 20) Δ Weeks 20 to 36
Energy (kcal)           0.500
 SAF 1,746±75 -154±92 1,547±14 141±144 0.938  
 CLA 1,925±96 -395±126 1,527±86 222±102 0.287  
Carbohydrate (g)           0.612
 SAF 197±10 -20±12 180±14 4±17 0.453  
 CLA 200±12 -28±15 184±10 -2±13 0.129  
Protein (g)           0.267
 SAF 78±4 -2±4 71±5 7±6 0.541  
 CLA 85±5 -10±6 74±4 3±5 0.333  
Fat (g)           0.578
 SAF 77±5 -10±6 63±7 15±9 0.606  
 CLA 85±6 -19±8 62±5 16±6 0.791  
PUFA (g)           0.448
 SAF 15±1 -2±2 12±2 4±2 0.594  
 CLA 18±2 -5±2 12±1 4±2 0.587  
Linoleic acid (g)           0.619
 SAF 13±1 -2±1 10±2 4±2 0.315  
 CLA 15±1 -3±2 11±1 4±2 0.739  
MUFA (g)           0.658
 SAF 30±2 -4±2 25±3 4±4 0.923  
 CLA 33±3 -9±3 24±2 6±3 0.589  
SFA (g)           0.891
 SAF 26±2 -3±2 21±3 7±3 0.386  
 CLA 26±2 -3±3 20±2 5±2 0.565  
Activity (Met eq)           0.475
 SAF 158±5 9±8 166±7 -3±13 0.706  
 CLA 161±7 -2±10 162±6 -7±9 0.516  

 1 All values are means ± SEMs.

Author Conclusion:
  • A significant reduction of BMI with 6.4g CLA supplementation per day was observed, which is supported in other studies. This weight loss may be attributed to reduction of adipose tissue mass.
  • SAF reduced trunk adipose mass in both diet periods and increased total body lean tissue mass and decreased trunk adipose obesity as assessed with DEXA
  • Supplementation with CLA and SAF exerted different effects on BMI, total and trunk adipose mass and lean tissue mass in obese post-menopausal women with type 2 diabetes
  • Supplementation with these dietary oils may be beneficial for weight loss, glycemic control or both.
Funding Source:
Government: National Center fo Research Resources (UL1RR025755) and the Clinical Research Center at The Ohio State University (M01-RR00034) from the NIH, the Caroline Kennedy Endowment.
Pharmaceutical/Dietary Supplement Company:
University/Hospital: The Ohio State University
Reviewer Comments:
  • Interactions between SAF and specific macronutrients were not tested
  • Although anthropometric measurements  (waist circumference and SAD) did not show a significant reduction in abdominal adipose, the use of DEXA found a decreased trunk adipose during SAF supplementation
  • Study population was obese post-menopausal women; therefore, the possibility to generalize results to non-obese men and women or to pre-menopausal women is limited
  • Energy and nutrient intakes were assessed with a repeated three-day diet record that may not reflect subtle changes in calories that may have occurred with the addition of 72kcal of oil per day
  • 16-week crossover interventions may not provide adequate time to show maximum results on changes in outcomes measured
  • There are limitations that occur in a free-living population that could be better measured in a controlled environment.
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.) No
  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")? Yes
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? Yes
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? Yes
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? 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? Yes
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)? N/A
  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