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DFA: Linoleic Acid (LA) and Intermediate Health Outcomes (2011)

Citation:

Madigan C, Ryan M, Owens D, Collins P, Tomkin GH. Dietary unsaturated fatty acids in type 2 diabetes: Higher levels of postprandial lipoprotein on a linoleic acid-rich sunflower oil diet compared with an oleic acid-rich olive oil diet. Diabetes Care. 2000 Oct; 23 (10): 1,472-1,477.

PubMed ID: 11023139
 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine the effect of a polyunsaturated fat diet compared with an isocaloric Mediterranean-style monounsaturated fat diet.

Inclusion Criteria:
  • Well-controlled diabetes mellitus
  • Regular attendance of DM clinic
  • No renal or hepatic disfunction
  • TG levels less than 4mmol/l
  • Not taking lipid-lowering agents
  • Stable weight and DM control for at least three months.
     
Exclusion Criteria:
  • Renal or hepatic dysfunction
  • Non-diabetic
  • TAG more than 4 ammo/Al
  • Patients on lipid-lowering agents
  • Unstable weight or diabetes control.

 

Description of Study Protocol:

Recruitment

Clients who regularly attend the diabetes clinic were recruited.

Design

Randomized cross-over study

Intervention

Patients were interviewed by a qualified dietitian and were randomly instructed on an isocaloric diet either high in monounsaturated, including 30ml olive oil daily, or high in polyunsaturated fat, including 30ml sunflower oil daily. After two weeks, patients were again seen by a dietitian and switched to the other diet.

Statistical Analysis

Statistical analysis was performed using the paired Student's T-test for comparison of fasting levels before and after treatment. Area under the curve measurements were obtained using Graphpad Prism 2 for Macintosh. Area under the curve analyses were made incrementally from fasting because fasting values are sometimes different in patients with diabetes. Correlation Coefficients were calculated for regression analysis inter- and intra- assay variation is expressed as the SD/mean x 100. P<0.05 was considered statistically significant.

 

Data Collection Summary:

Timing of Measurements

At the end of each dietary period, fasting blood was taken, and patients were given a high-fat breakfast containing a 50g glucose load, which was consumed over 30 minutes. The meal consisted of a serving of orange juice containing 50g glucose, 30g cereal with 0.5g milk, two slices of white bread fried in a commercial sunflower or olive oil (30ml), two fried eggs, two fried tomatoes and a cup of coffee or tea. Blood was sampled every two hours over the next eight hours.

Plasma and lipoprotein cholesterol levels were measured by enzymatic colorimetric methods using commercially available kits.  Plasma and lipoprotein triglycerides and phospholipids were measured with kits from BioMerieux. Chylomicron, VLDL-, LDL- and HDL- protein was estimated by modification of the Lowry method. BG was measured by an enzymatic method and HgbA1c was determined using an enzyme immunoassay method. Serum total insulin was measured using a microparticle enzyme immunoassay. 

Dependent Variables

  • Chylomicron
  • VLDL
  • Fasting blood glucose
  • Plasma cholesterol
  • Plasma TG.

Independent Variables

  • High-monounsaturated fat diet
  • High-polyunsaturated fat diet.

 

Description of Actual Data Sample:
  • Initial N: 11 males
  • Attrition (final N): 11
  • Age: 56.0±2.5 years
  • Ethnicity: Not applicable
  • Anthropometrics: BMI linoleic acid diet: 27.7±2.6; oleic acid diet: 27.8±2.2
  • Location: Ireland.

 

Summary of Results:

Key Findings for Subjects on Diets

Variables Linoleic Acid Diet Oleic Acid Diet P-Value
Fasting glucose  8.5±0.8  7.6±0.7  <0.01
Fasting insulin  13.4±2.9  11.8±2.3  <0.02
Plasma cholesterol  5.3±0.6  4.9±0.5  <0.001
Plasma triglycerides  1.9±0.9  1.7±0.6  NS

 

  Linoleic Acid Diet (fasting) Oleic Acid Diet (fasting) Linoleic Acid (postprandial) Oleic Acid (postprandial)
Chylomicron  
   Apo B48 3.1±1.5  P<0.05 1.6±1.7 38±21  P<0.05 22±10
   Cholesterol 14.0±13.2 9.6±8.1 180±100 140±136
VLDL     
   Apo B48 1.7±1.6 1.3±0.8 11±9  P<0.05 4±2
   Cholesterol 66.0±37.2 78.1±88.4 355±301 465±668


 

Author Conclusion:

The objective of this study was to examine the effect of a polyunsaturated fat diet compared with an isocaloric Mediterranean monounsaturated fat diet in diabetic men. Chylomicron remnant particles, especially the small particles, are thought to be atherogenic. The major finding in this study is that a linoleic acid diet in diabetic patients increases the number of chylomicrons and VLDL, apo B48, and apo B100 particles, with each particle containing less lipid. The linoleic acid diet was associated with increased fasting insulin and glucose levels, increased postprandial lipoproteins, and significantly higher plasma and LDL cholesterol levels. This study suggests that an oleic acid-rich Mediterranean-type diet may be preferable for people with type 2 diabetes.

Funding Source:
Government: Health Research Board of Ireland
Industry:
Bristol-Myers Squibb
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:
  • The diets were isocaloric
  • There was no difference in BMI between diets (except oil used).
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? Yes
  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? No
  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)? Yes
  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? No
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