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HTN: Omega-3 Fatty Acids (2007)


Dyerberg J, Eskesen DC, Andersen PW, Astrup A, Buemann B, Christensen JH, Clausen P, Rasmussen BF, Schmidt EB, Tholstrup T, Toft E, Toubro S, Stender S. Effects of trans- and n-3 unsaturated fatty acids on cardiovascular risk markers in healthy mailes. An 8 weeks dietary intervention study. Eur J Clin Nutr. 2004; 58: 1,062-1,070.

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 purpose was a comparative study of the effects of marine n-3 PUFA and industrially produced trans-fatty acids on markers of cardiac risk.

Inclusion Criteria:
  • 20 to 60 years of age
  • Normal ECG and blood pressure
  • Apparently healthy with no abnormalities in routine biochemical and hematological tests
  • All subjects were male although this was not stated with other inclusion criteria.
Exclusion Criteria:
None specified.
Description of Study Protocol:
  • Recruitment: Public advertisement

  • Design: The study was a randomized double-blind, parallel eight-week dietary intervention trial with a 12-week follow-up period

  • Blinding used: Subjects were blinded as to which treatment they were randomized to and it is assumed the investigators were blinded to which subjects were on specific treatments.


The intervention (treatment) were daily intakes of either:

  • 33g trans-fatty acids (TFA) fat consisting of partially hydrogenated soy oil containing 60% TFA (20g TFA)
  • 12g fish oil with approximately four grams of n-3 PUFA and 21g of control fat
  • 33g of conrol fat with 60% saturated fatty acids (20g), with middle fractions of palm oil used to supply the fat.

These fats were baked into rolls and cakes for daily consumtion and distributed to subjects in one- to two-week lots as frozen product. Daily intake of two rolls and a piece of cake isocalorically replaced similar items in the subjects' usual diets for eight weeks.

Statistical Analysis

  • Unpaired T-tests were used to analyze comparisons between the groups and within-group differences were tested with a paired T-test

  • Chi square tests were used to test for differences in nominal data

  • P-values of <0.05 were used for significance.

Data Collection Summary:

Timing of Measurements

  • Measurements occured at baseline after 10 hours of fasting

  • BP measured after 10 minutes of rest in sitting position

  • Measurements were also completed at the end of intervention (eight weeks after baseline) and at follow-up (12 weeks after baseline).

Dependent Variables

  • Variable One: Systolic and diastolic BP, mean arterial pressure
  • Variable Two: Plasma lipids and lipoproteins
  • Variable Three: Heart rate variability
  • Variable Four: Arterial dilatory capacity, arterial compliance and distensibility.

Independent Variables

  • TFA group: 33g of partially hydrogenated soy oil, containing 20g of TFA given daily for eight weeks
  • n-3 PUFA group: 12g fish oil with four grams n-3 fatty acids and 21g control fat
  • Control group: 33g of control fat consisting of 60% saturated fatty acids.

Control Variables

Study groups were comparable for demographic data (age and BMI), smoking, physical activity and fish intake.

Description of Actual Data Sample:


  • Initial N: 93 male volunteers recruited, 87 qualified for enrollment
  • Attrition (final N): 79 completed the eight-week intervention (one was excluded for poor compliance, two left for private reasons, three excluded due to difficulties consuming the diets and two left with no explanation)


  • TFA group: 35.3±10.3 years (mean±SD)
  • n-3 PUFA group: 39.2±10.5
  • Control group: 37.6±10.6.


Not given.


Groups were the same with respect to BMI:

  • TFA group: 24.7±4.0 (mean±SD)
  • n-3 PUFA group: 24.9±3.2
  • Control group: 24.1±3.7.

At the end of the intervention, body weight for each of the groups did not differ from baseline.

Body Weight Before and After Intervention by Group (Mean±SEM)


TFA Group

n-3 PUFA Group

Control Group

Body Weight (kg) Before




Body Weight (kg) After





Dept. of Human Nutrition, The Royal Veterinary and Agricultural University, Frederiksbeerg, Denmark.

Summary of Results:

Systolic (SBP), Diastolic (DBP) and Mean Arterial Pressure (MAP) at Baseline, After Eight Weeks of Intervention and at Follow-up 12 Weeks after Baseline


TFA Group

n-3 Group

Control Group

SBP Before




SBP After




SBP Follow-up (N=27)




DBP  Before




DBP After




DBP Follow-up




MAP  Before




MAP After




MAP Follow-up (N=26)




All values expressed in mmHg as mean±SEM
*Minor decrease in MAP in n-3 group after intervention, different from control group, P<0.05.

  • No significant changes were found in any group from baseline or between groups, with the exception of the MAP decrease after intervention for the n-3 group.
  • Intervention diets resulted in 5% iof energy increases in fat consumption for all groups
  • An increase in TFA intake of 6% of energy from the experimental diet occured in the TFA group and a similar increase was found in the SFA intake in the control group
  • The 12g fish oil in the n-3 PUFA group yielded significantly lower SFA intake, compared to the control group. However, fatty acid patterns measured in platelet membranes indicate good compliance to the diets.

Other Findings

  • HDL-C fell in the TFA group and triglycerides fell in the n-3 PUFA group after intervention, different from the control group
  • There was no overall effect seen on heart rate variability indices, compared to the control group
  • There was no effect of diet on arterial dilatory capacity or compliance and distensibility measures
  • Suggestion of TFA increasing heart rate in healthy volunteers.
Author Conclusion:
  • The author's found no effect of the TFA diet on BP and only a modest decrease in MAP following an eight-week intervention of an n-3 PUFA supplemented diet
  • The results indicate that the association between coronary heart disease risk and intake of TFA and n-3 PUFA relates only modestly to changes in traditional risk markers.
Funding Source:
University/Hospital: Royal Veterinary and Agricultural University, Aalborg Hospital, Arhus University Hospital, Rigshospital, Gentofte University Hospital (all Denmark)
Reviewer Comments:
  • Dietary TFA was estimated at 2.6g per day for the usual dietary intake to correspond with the mean intake in Denmark
  • This value was subtracted from the calculated saturated fat content of the subjects' diets
  • The n-3 fatty acid intake in the subjects' usual diet is included in the total PUFA intake estimation.
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? No
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? 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? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? ???
  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.) ???
  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? N/A
  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? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? N/A
  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