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Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
- To investigate whether dietary monounsaturated fatty acids (MUFA), compared with saturated fatty acids (SFA) affects blood pressure (BP) in healthy adults
- A secondary purpose was to investigate whether the addition of long-chain n-3 fatty acids had an effect on BP.
Inclusion Criteria:
- Healthy adults
- Normotensive
- Normal or moderately increased body weight [body mass index (BMI): 22 to 32kg/m2]
- Impaired glucose tolerance was acceptable.
Exclusion Criteria:
- Diabetes
- Specific eating habits, due to cultural or religious beliefs
- High habitual physical exercise
- High alcohol intake (binge drinking or a regular intake of over 40g alcohol per day)
- Hepatic, cardiac, thyroid or disabling disease
- Body weight change during past three months of over 4kg
- Subjects taking acetyl salicylic acid, thiazide diuretics, beta blockers, lipid-lowering drugs or corticosteroids.
Description of Study Protocol:
Design
- Three-month controlled parallel, multi-center study with a two-week run-in period, followed by randomization to one of two groups: MUFA or SFA
- Within each of the two groups, there was further randomization to receiving supplementary n-3 fatty acids or a placebo of olive oil.
Blinding Used
Subjects were blinded to n-3 fatty acid or olive oil supplementation.
Intervention
- Isoenergetic diets with the same amount of macronurients were consumed for three months
- 37% of kilocalories from fat was used for both the high-MUFA and the high-SFA diets
- The MUFA diet consisted of 8% of kilocalories from SFA, 23% from MUFA and 6% from PUFA
- The SFA diet consisted of 17% SFA, 14% from MUFA and 6% from PUFA
- Randomized subgroups from the MUFA group and from the SFA group received additional fish oil capsules with 3.6g n-3 fatty acids per day (2.4g as EPA and DHA)
- Trained dietitians instructed all subject on preparation of their diets and met with subjects at least every other week until the end of the study
- Edible fats were supplied to use as spreads, for cooking and in dressings that contained negligible amounts of trans fatty acids, n-3 fatty acids or olive oil.
Statistical Analysis
- Data were analyzed as an intention to treat study including all randomized subjects with at least one measurement during treatment. A statistical model that is not described was used with treatment categories of SFA or MUFA with or without n-3 fatty acids and their interaction analyzed as factors. Center, age, sex and baseline value of the outcome variable were covariates. A post hoc subgroup analysis of total fat intake above or below 37% of kilocalories was conducted
- Student's unpaired T-tests were used to determine differences between groups.
Recruitment
Not discussed.
Data Collection Summary:
Timing of Measurements
- BP was measured at baseline and at the end of the study (three months)
- Weight was measured at each visit (every two weeks).
Dependent Variables
- Variable One: Diastolic BP (DBP)
- Variable Two: Systolic BP (SBP)
- Both DBP and SBP were measured to the nearest five mmHg with a sphygmomanomeer in a sitting position, after 10 minutes of rest
- Measurements were done three times at two-minute intervals and a mean value was used.
Independent Variables
- SFA diet: 37% of energy as fat with high proportion of SFAs
- MUFA diet: 37% of energy as fat with high proportion of MUFAs
- Fish oil supplement (3.6g n-3 fatty acids per day providing 2.4g EPA and DHA).
Control Variables
Placebo (olive oil) supplement.
Description of Actual Data Sample:
- Initial N: 162
- 95 men
- 67 women
- Attrition (final N): 162 because of intent to treat analysis, however three dropped out
- Age:
- 30 to 65 years
- SFA/placebo group (N=42): 49.3±7.1 (mean±SD)
- SFA/n-3 FA group (N=41): 48.5±8.0
- MUFA/placebo group (N=40): 47.0±8.8
- MUFA/n-3 FA group (N=39): 49.5±7.3
- 30 to 65 years
- Ethnicity: Not described
- Other Related Demographics: None given
- Anthropometrics:
- BMI was not different between groups, nor did it change during the course of the study
- BMI (kg/m2)
- SFA/placebo group: 26.3±2.7
- SFA/n-3 group: 26.9±3.0
- MUFA/placebo group: 26.1±3.2
- MUFA/n-3 group: 26.5±3.1
- Location:
- Denmark
- Sweden
- Finland
- Italy
- Australia.
Summary of Results:
There were no differences between the groups for SBP or DBP at baseline.
Effect of Three-Month Dietary Intervention and n-3 Fatty Acids on DBP and SBP
SFA Baseline | SFA Change | P-value | MUFA Baseline | MUFA Change | P-value | Mean Difference; 95% CI |
P-value | |
DBP (mmHg) Placebo | ||||||||
<37% of energy |
76.2±6.8 | 1.9±8.2 | 0.07 | 78.3±11.8 | -4.8±8.5 | 0.02 | 6.4; 2.3, 10.5 | 0.0023 |
>37% of energy |
78.2±8.4 | -2.7±5.3 | 0.01 | 77.3±8.1 | -2.1±7.8 | 0.18 | -1.7; -5.6, 2.2 | 0.3973 |
DBP n-3 fatty acids | ||||||||
<37% of energy |
74.4±8.7 | -1.0±6.4 | -1.3 | 74.2±9.0 | -2.3±6.3 | 0.09 | 1.7; -2.3, 5.7 | 0.4107 |
>37% of energy |
79.7±8.6 | -1.3±6 | -1.6 | 74.9±9.6 | -3.4±5.1 | 0.02 | 1.8; -2.4, 5.9 | 0.3940 |
SBP Placebo |
||||||||
<37% of energy |
112.4±10.3 | 3.5±11.6 | 0.16 | 125.8±16.8 | -4.8±8.2 | 0.15 | 6.6; 0.3, 12.9 | 0.0408 |
>37% of energy |
120.8±12.8 | -3.2±5.7 | 0.0524 | 120.7±16.4 | -2.4±11.6 | 0.26 | -1.9; -7.9, 4.1 | 0.5286 |
SBP n-3 fatty acids |
||||||||
<37% of energy |
121.1±11.1 | -2.1±13.2 | 0.29 | 125.0±10.1 | -2.3±10.9 | 0.29 | -0.1; -6.3, 6.0 | 0.9691 |
>37% of energy | 124.1±11.7 | -1.4±7.1 | 0.56 | 119.5±15.4 | -3.2±11.9 | 0.28 | 1.3; -5.0, 7.7 | -0.6802 |
- There was a significant drop from baseline in SBP for the MUFA treated group (-2.2%; P=0.009) and for DBP (-3.8%; P=0.0001) without significant changes for the SFA diet group
- The MUFA diet caused lower DBP than the SFA diet (P=0.0475)
- The table above shows the changes from baseline with the added covariate of less than or more than 37% of total kilocalories as fat
- When total fat was under 37%, the MUFA diet reduced SBP and the DBP
- These differences disappeared when fat intake was above 37% of kilocalories
- There was no effect of added n-3 fatty acids.
Author Conclusion:
- Decreasing SFA and increasing MUFA decreased DBP
- The beneficial effect on BP from type of fat was negated by consumption of a high total fat intake (>37% of kilocalories from fat)
- The addition of n-3 fatty acids had no effect on BP.
Funding Source:
Government: | Danish Medical Research Council, Health Research Council Academy of Finland, Swedish Council for Forestry and Agricultural Research | ||||
Industry: |
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University/Hospital: | Aarhus University Hospital (Denmark), University of Uppsala (Sweden), University of Kuopio (Finland), Federico II University (Italy), University of Wollongong (Australia) | ||||
In-Kind support reported by Industry: | Yes |
Reviewer Comments:
- Double-blinding was not used
- Weight, exercise and smoking habits were kept stable for the duration of the study
- Compliance was checked by diet records and serum phospholipid fatty acid composition
- There was a slightly higher dietary fiber intake and lower cholesterol intake by the MUFA group
- There was no difference in calculated dietary intakes of calcium, sodium, potassium and alcohol between the groups.
Quality Criteria Checklist: Primary Research
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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? | ??? | |
2. | Was the selection of study subjects/patients free from bias? | ??? | |
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? | ??? | |
3. | Were study groups comparable? | No | |
3.1. | Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) | No | |
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")? | N/A | |
4. | Was method of handling withdrawals described? | Yes | |
4.1. | Were follow-up methods described and the same for all groups? | No | |
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? | ??? | |
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? | ??? | |
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? | 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? | 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 | |