DLM: Soy (2001)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

"To investigate the effect of soy  protein and isoflavones on blood lipid profiles and mononuclear cell LDL receptor mesenger RNA (mRNA) in postemenopausal women over a 6-month feeding period."

Inclusion Criteria:
  1. >1 year since last menstrual period
  2. T chol: 6.2 – 7.8 mmol/L
Exclusion Criteria:
  1. Hormone replacement therapy or other drugs that lower cholesterol
  2. Diabetes mellitus
  3. Thyroid disease
  4. Chronic disease
  5. Allergy to soybeans
Description of Study Protocol:

Recruitment:  flyers,letters, and physician referrals

Study Design: 24 week cohort studies of women on Step I diets plus random assignment to 1of 3 study diets incorporating 40 g protein from one of the following:

Intervention

  1. casein + nonfat dry milk
  2. 56 mg total aglycone isoflavones/d (ISP56)
  3. 90 mg total aglycone isoflavones/d (ISP90)

Basal diet for 2 weeks; Experimental diet 24 weeks.

Statistical analysis

  • multiple linear-regression analyses comparing lipid changes from baseline with intervention
  • one-way analysis of variance used to determine differences between groups for BMI, physical activity, and nutrient intake at each time point
  • paired t test to evaluate changes from baseline within groups

 

Data Collection Summary:

Timing of Measurements

  • Blood sampling on 2 days of the basal diet and q 6 weeks on the experimental diet.

  • 3-day dietary intake records assigned on random days every 4 weeks

  • physcial activity records obtained during same days as dietary records

Dependent variables

  • Serum lipids
  • Mononuclear cell LDL receptor messenger RNA

Independent variables

  • isoflavone intake
    • ISP56, containing 56 mg total aglycone isoflavones
    • ISP90, containing 90 mg total aglycone isoflavones

Control Variables

  • nutrient intake
  • physical activity
  • BMI
Description of Actual Data Sample:

Number of Subjects:  134 women screened; 84 gave informed consent

Final Number (attrition): 74; 66 included in statistical analyses

Age:  49-83y

Demographics: none reported

Anthropometric data: BMI:  means for groups range 26.2-29.1., no significant difference between groups

Location:  Champaign-Urbana, Illinois, USA

 

Summary of Results:

Dietary intake, BMI, physical activity

  • energy intake and intakes of all nutrients, except protein, showed no significant differences between groups
  • protein intake significantly greater than baseline for all three groups at 24 weeks
  • no changes in physical activity or BMI frpm baseline or between groups

Plasma lipids

  • no significant changes in total cholesterol in any groups over 24 weeks
  • Non-HDL cholesterol in both the ISP56 and ISP90 groups was decreased compared with the casein group (P<0.05).
  • HDL cholesterol ­ was greater at 18 and 24 weeks in both the ISP56 and ISP90 groups compared with the casein group (P<0.05).
  • HDL decreased by 4.1% in the casein group; HDL increased by 5.2% in ISP56 group and 3.6% in ISP90 group

LDL receptor mRNA

  • Compared with baseline mononuclear cell LDL receptor messenger RNA concentrations increased 27% in ISP56 group, increased 75% in ISP90 group and reduced 26% in casein group (P<0.01).
Author Conclusion:

Soy protein, with different amounts of isoflavones, may decrease the risk of cardiovascular disease via improved blood lipid profiles, and that the mechanism by which apolipoprotein B-containing lipoproteins were depressed may be via alterations in LDL receptor quantity or activity.

Funding Source:
Government: NIMH
Reviewer Comments:

a carefully designed study

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? Yes
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? 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? Yes
  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? No
  6.6. Were extra or unplanned treatments described? No
  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)? No
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? No
  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