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DM: Omega-3 Fatty Acids (2014)

Citation:

McManus RM, Jumpson J, Finegood DT, Clandinin MT, Ryan EA. A comparison of the effects of n-3 fatty acids from linseed oil and fish oil in well-controlled type II diabetes. Diabetes Care, 1996; 19 (5): 463-467.

PubMed ID: 8732710
 
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 purpose of this study was to compare the effects of linseed oil (LO) with fish oil (FO) supplementation in subjects with type II diabetes.

Inclusion Criteria:
  • Diagnosis of non-insulin dependent type II diabetes by the National Diabetes Data Group
  • Provided written informed consent.
Exclusion Criteria:
Not described.
Description of Study Protocol:
  • Recruitment: Subjects with non-insulin requiring type II diabetes were recruited from a tertiary care center and offered participation in the study
  • Design: Randomized crossover trial
  • Blinding used: Double-blind.

Intervention

  • Subjects were randomly assigned by order of recruitment to one of two orders of oil supplementation:
    • Olive oil, fish oil and linseed oil
    • Olive oil, linseed oil and fish oil.
  • All subjects underwent a three-month run-in period of olive oil placebo before three months of fish oil or linseed oil
  • After the three months of N-3 oil treatment, subjects underwent crossover to the alternative oil for a final three months of supplementation
  • Olive oil was given at a dose of 35mg 18:1 FA per kg body weight per day
  • Linseed oil was prescribed at a dose of 35mg 18:3 N-3 per kg body weight per day
  • Fish oil was given at a dose of 35mg 20:5 N-3 and 22:6 N-3 (total combined) per kg body weight per day.

Statistical Analysis

  • Student's paired T-tests were used to compare basal and placebo periods in the diabetic population
  • Analysis of variance was performed to determine the effect of the dietary oil supplementations
  • All analyses were performed with the Statistical Analysis System (SAS, Cary, NC) on a desktop computer; results are reported as means ±SE.
Data Collection Summary:

Timing of Measurements

Measurements made at baseline and after each three-month period.

Dependent Variables

  • Weight and height were recorded at baseline
  • Lipid, glucose and insulin parameters: An intravenous catheter was used to measure blood glucose, HbA1c, insulin, cholesterol, triglyceride and HDL- and LDL-cholesterol values
  • Each individual also underwent an insulin-modified fasting glucose tolerance test (FSIGT)
  • After four baseline blood samples were taken over 15 minutes, a bolus injection of 50% dextrose (300mg per kg) was given over one minute. Subsequent samples for glucose and insulin were taken at times 1, 2, 3, 4, 5, 7, 9, 11, 13, 15, 18. At 20 minutes, a bolus injection of regular insulin was given over one minute at a dose of 0.05U per kg.

Independent Variables

  • Subjects were randomly assigned by order of recruitment to one of two orders of oil supplementation:
    • Olive oil, fish oil and linseed oil
    • Olive oil, linseed oil and fish oil.
  • All subjects underwent a three-month run-in period of olive oil placebo before three months of fish oil or linseed oil
  • After the three months of N-3 oil treatment, subjects underwent crossover to the alternative oil for a final three months of supplementation
  • Olive oil was given at a dose of 35mg 18:1 FA per kg body weight per day
  • Linseed oil was prescribed at a dose of 35mg 18:3 N-3 per kg body weight per day
  • Fish oil was given at a dose of 35mg 20:5 N-3 and 22:6 N-3 (total combined) per kg body weight per day
  • Participants completed seven-day food diaries at the end of each three-month period of supplementation and these were evaluated using a nutritional database derived from the nutrient data bank set up within the computer system of the University of Alberta
  • Participants continued their routine medications and diabetic meal plans throughout and were counseled to maintain an isocaloric diet for the duration of the study.
Description of Actual Data Sample:
  • Initial N: 11 subjects
  • Attrition (final N): 11 (three women, eight men)
  • Age: Mean, 61.8±2.9 years
  • Ethnicity: Not reported
  • Other relevant demographics: Not reported.
Anthropometrics
  • Mean weight: 81.5±4.2kg
  • Mean BMI: 27.8±1.1kg/m2
Location

Alberta, Canada.

Summary of Results:

Key Findings

  • HbA1c and lipid values were within the normal range at randomization
  • Repeated measures analysis of variance testing found no significant differences in weight, fasting glucose, fasting insulin, HbA1c, total cholesterol, LDL-cholesterol and HDL-cholesterol levels with either active oil
  • Fish oil was associated with significant reductions in triglycerides and a trend toward decreased insulin sensitivity.
Author Conclusion:
  • In a population with well-controlled type II diabetes, three months of fish oil, but not linseed oil, resulted in lowered triglyceride levels
  • Neither linseed oil nor fish oil significantly affected glycemic control, cholesterol values or insulin secretions, while a nonsignificant trend toward decreased insulin sensitivity was found with fish oil.
Funding Source:
Not-for-profit
Canadian Dairy Bureau and the Natural Sciences and Engineering Research Committee
Foundation associated with industry:
Other non-profit:
Reviewer Comments:

Small sample size.

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? No
  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? 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)? 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? 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