HTN: Protein (2007)

Study Design:
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Quality Rating:
Research Purpose:
To examine the potential benefit from providing functional foods containing added fish oils or soya-protein to people with elevated risk for coronary vascular disease, in the absence of any other forms of dietary or lifestyle advice.
Inclusion Criteria:
  • Total serum cholesterol of at least 5.7mmol per L
  • Mean systolic blood pressure at least 130mm Hg
  • Either or both of the above risks.
Exclusion Criteria:
Taking medication for blood pressure or cholesterol.
Description of Study Protocol:
  • Recruitment: Random selection from 12 general practices attending a screening consultation
  • Design: Double-blind factorial placebo-controlled randomized trial (RTC), with three arms of intervention plus the placebo group
  • Blinding used: Double-blinding (staff and subjects).


Four groups as follows:

  • DHA Group: Received white bread rolls, cereal bars and cracker biscuits with DHA added equal to two grams DHA per day for five weeks
  • Soya Group: Received white bread rolls, cereal bars and cracker biscuits with soya protein added equal to 25g soya protein per day and 50mg isoflavonoids for five weeks
  • DHA and Soya Group: Received products listed above with both DHA and soy protein added in the amounts given above
  • Placebo Group: Received products listed above without DHA or soya protein added.

Statistical Analysis

  • Main effects of DHA and soy protein were tested with a two-way analysis of covariance. Covariates included baseline values for systolic and diastolic blood pressure. A test for interaction of DHA and soy protein was conducted in men and women separately.
  • The analysis was based on intent-to-treat and included all participants originally randomized into the study
  • A power test indicated 50 participants per group were needed to detect a 10% difference from placebo at 90% power
  • There were 50 to 59 subjects per group.


Data Collection Summary:

Timing of Measurements

Measurements were taken at baseline and at five weeks following intervention.

Dependent Variables

  • Variable One: Systolic and diastolic blood pressure meaured with an automated sphygmomanometer using the average of three readings taken at 10-minute intervals in a resting seated position
  • Variable Two: Total serum cholesterol
  • Variable Three: LDL-C
  • Variable Four: HDL-C.

Independent Variables

  • Bread products with two grams DHA per day
  • Bread products with 25g soy protein per day
  • Bread products with two grams DHA plus 25g soy protein per day.

Control Variables

Bread products without added DHA or soya protein.
Description of Actual Data Sample:
  • Initial N: 311
  • Attrition (final N): 213 (112 men); original patients who did not meet study criteria of total serum cholesterol of at least 5.7mmol per L or mean systolic blood pressure of at least 130mm Hg or were taking medication for blood pressure, were excluded
  • Age: 45 to 59 years; 52±4 (mean±SD) years for each group
  • Ethnicity: Not specified, however all subjects were from Lewis and Harris Island off the northwest coast of Scotland, UK
  • Other relevant demographics: This island was selected because the inhabitants had the second highest value for mean serum cholesterol of 60 participating centers around the world.

Anthropometrics: BMI at Baseline


DHA + Soya





BMI (mean±SD)






There were no differences between groups.


Island of Lewis and Harris, off of the northwest coast of Scotland.

Summary of Results:
  • No significant interactions were observed between soya protein and DHA
  • No significant effects were observed on blood pressure (see table below)
  • The effect of DHA on systolic blood pressure (SBP) and diastolic blood pressure (DBP), compared with placebo
  • Intention to treat and as-treated analysis.




Adjusted Mean (SE)

Percentage Treatment Effect
(95% CI)


Adjusted Mean (SE)

Percentage Treatment Effect
(95% CI)




125.79 (0.95)

-0.43% (-3.29, 2.43)


125.79 (1.33)

-0.94% (-4.68,2.79)




125.85 (0.91)



126.48 (1.16)





76.22 (0.53)

-1.59% (-4.19, 0.99)


76.39 (0.75)

-2.19% (-5.57,1.18)




77.95 (0.51)



78.26 (0.65)


Other Findings

  • DHA increased HDL-C by 6.0% (95% CI 2.4%, 9.6%) for intent-to-treat analysis and an increase of 9.6% (95% CI 4.3%, 13.9%) was seen in those who attended follow-up
  • An analysis of interaction of sex and soy protein revealed that women given soya protein had increased SBP from a mean of 121.16mm Hg at baseline to 126.89mm Hg following the intervention. This represents a 5.9% increase in SBP (95% CI: 1.73, 9.9%). This finding was not present in men.
Author Conclusion:
  • No important significant effect was observed overall from DHA on LDL-C or total cholesterol or on systolic and diastolic blood pressure
  • Adding DHA to foods eaten on a regular basis may be a simple way to increase HDL-C among middle-aged men and women.
Funding Source:
Roche Vitamins
Pharmaceutical/Dietary Supplement Company:
University/Hospital: St. Luke's Hospital Foundation
Reviewer Comments:
  • This was an intent-to-treat study, so change in body weight, physical activity and diet were not monitored
  • Analysis included all participants (intent-to-treat) and those who returned for follow-up ('as-treated')
  • Compliance was defined as eating at least 80% of the study foods and with biochemical markers, however no mention was given if non-compliers were excluded from data analysis
  • Plausible reasons for lack of effect could be the dose used, tested only DHA on its own rather than with EPA, chance randomization among groups may not have controlled for potential confounding variables, longer follow-up may be needed to determine long-term effects of functional foods.
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? N/A
  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? 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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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.) No
  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? ???
  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? Yes
  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? No
  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)? No
  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? 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