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DM: Omega-3 Fatty Acids (2014)

Citation:

Goh YK, Jumpsen JA, Ryan EA, Clandinin MT. Effect of omega-3 fatty acid on plasma lipids, cholesterol and lipoprotein fatty acid content in NIDDM patients. Diabetologia, 1997; 40 (1): 45-52.

PubMed ID: 9028717
 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

The aim of this study was to determine the effect on the plasma triacylglycerol and lipoprotein cholesterol level after consumption of 20:5 omega-3 and 22:6 omega-3 or 18:3 omega-3 in physiological amounts that could be achieved by the consumption of normal foods.

Inclusion Criteria:
  • Non-insulin dependent type 2 diabetic
  • No cardiac complications
  • Provided written informed consent.
Exclusion Criteria:
Patients on lipid-lowering drugs were excluded.
Description of Study Protocol:
  • Recruitment: Patients treated for non-insulin dependent diabetes mellitus (NIDDM) were recruited from the outpatient Metabolic Clinic at the University of Alberta Hospital
  • Design: Randomized crossover study
  • Blinding used: Double-blind.

Intervention

  • Participants initially given an olive oil supplement (placebo) equivalent to 35mg of 18:1 per kg body weight per day for three months
  • This was followed by two supplement periods in a randomized crossover fashion for three months:
    • Linseed oil capsule equivalent to 35mg of 18:3 omega-3 per kg body weight per day
    • Fish oil capsule equivalent to 35mg of 20:5 omega-3 plus 22:6 omega-3 per kg body weight per day.

Statistical Analysis

  • Data collected from the two groups of participants when they entered the study were initially compared byT-test at the P<0.05 level
  • The effect of omega-3 fatty acid supplementation on plasma triacylglycerol and total, HDL- and LDL-cholesterol was analyzed by repeated-measures analysis of variance (ANOVA), using SAS statistical software
  • Significant differences among means as revealed by the F-test of ANOVA on the P:S ratio or type of oil supplement were further compared by a Duncan Multiple Range Test at the P<0.05 level
  • To compare the effects of feeding 18:3 omega-3 linseed oil, 20:5 omega-3 and 22:6 omega-3 (fish oil) on the arachidonate and polyunsaturated fatty acid content in the lipoproteins, the change in fatty acid content of each was also calculated for both dietary P/S groups by subtracting the fatty acid levels of the olive oil treatment period from the fatty acid levels of the fish oil and linseed oil treatment
  • This difference was compared by Student's paired T-test (P<0.05)
  • The Pearson correlation coefficient was used to determine the presence of any overall correlations between clinical data and selected dietary fat intake variables.
Data Collection Summary:

Timing of Measurements

Measurements made at baseline and at the end of each three-month period.

Dependent Variables

  • Plasma triacylglycerol and cholesterol levels: Blood samples were drawn at baseline and after each supplement period to determine levels of lipid, lipoprotein, insulin, glucagon and C-peptide analyses
  • Fatty acid methyl esters were prepared and separated by automated gas-liquid chromatography (GLC).

Independent Variables

  • Participants initially given olive oil supplement (placebo) equivalent to 35mg of 18:1 per kg body weight per day for three months
  • This was followed by two supplement periods in a randomized crossover fashion for three months:
    • Linseed oil capsule equivalent to 35mg of 18:3 omega-3 per kg body weight per day
    • Fish oil capsule equivalent to 35mg of 20:5 omega-3 plus 22:6 omega-3 per kg body weight per day.
  • At the end of each three-month period, a seven-day dietary record was completed to calculate dietary fat intake and P:S ratio
  • A dietitian collected all food and drink consumption for seven days. Dietary intake, including energy to total fat, saturated and unsaturated fatty acids as well as cholesterol were calculated.
Description of Actual Data Sample:
Initial N

28 subjects (sex not specified).

Attrition (Final N)

28 subjects.

Mean Age

  • Low Dietary P/S Group (N=18): 56.2±1.8 years
  • High Dietary P/S Group (N=10): 59.7±3.0 years.
Ethnicity

Not reported.

Other Relevant Demographics

Not reported.

Anthropometrics

Subjects served as own controls in crossover trial.

Location

Alberta, Canada.

Summary of Results:

Key Findings

  • Fish oil significantly reduced plasma triacylglycerol levels (P<0.05) and increased 20:5 omega-3 and 22:6 omega-3 content of all lipoprotein lipid classes
  • Linolenic acid supplementation had no effect on plasma triacylglycerol level, but it increased 18:3 omega-3 content of lipoprotein cholesterol ester fractions (P<0.05)
  • A slight increase in 20:5 omega-3 but not in 22:6 omega-3 content was noted in lipoprotein lipid classes as a result of 18:3 omega-3 supplementation
  • LDL- and HDL-cholesterol, insulin, glucagon and C-peptide levels were not affected by either omega-3 supplement.
Author Conclusion:

A modest intake of omega-3 fatty acids will reduce plasma triglyceride levels without affecting LDL- or HDL-cholesterol levels.

Funding Source:
Government: Natural Sciences and Engineering Research Council of Canada
Not-for-profit
Dairy Bureau of Canada
Foundation associated with industry:
Reviewer Comments:
  • A small number of subjects were studied
  • The sample was not well described.
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? No
  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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  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? 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)? 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? No
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