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HTN: Protein (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To reevaluate the evidence on soy protein and CVD and to update the scientific advisory bases on assessment of more recent work including soy protein and isoflavones with a focus on blood LDL-C.
Inclusion Criteria:
  • Studies of soy protein with isoflavones and effect on BP
  • Also reviewed studies of soy protein with and without isoflavones for effects on LCL-C and lipoprotein(a)
  • Reviewed studies of soy isoflavones for effects on menopausal vasomotor symptoms, osteoporosis and cancer of prostate, breast and endometrium.
Exclusion Criteria:
Not applicable.
Description of Study Protocol:
  • Recruitment: Not applicable
  • Design: Review of several studies from 1994 to 2005, including some meta-analyses.
  • Statistical Analysis: Not applicable.

 

Data Collection Summary:

Timing of Measurements

Not applicable. 

Dependent Variables

  • LDL-C and lipoprotein(a)
  • BP
  • Health conditions related to estrogens: Menopausal vasomotor symptoms, osteoporosis, cancer of the breast, endometrium and prostate.

Independent Variables

  • Soy protein
  • Soy isoflavones.
Description of Actual Data Sample:
  • Initial N: Not applicable
  • Attrition (final N): Not applicable
  • Age: At least 26 years, for studies of effects of soy and isoflavones on serum lipids; not stated for studies investigating effects on BP
  • Ethnicity: Not stated
  • Other relevant demographics: Not stated
  • Anthropometrics: Not stated
  • Location: Worldwide studies.

 

Summary of Results:

Other Findings 

  • Six studies (2000-2003) testing the effect of soy protein with isoflavones compared with casein or milk protein on BP were reviewed. Blood pressure decreased significantly in one study, but not in the other five studies (data not shown), with the average change -1mm Hg for SBP.
  • Five other studies (1997-2002), investigating the effect of soy isoflavones on BP did not find a significant effect
  • Soy protein with isoflavones reduced LDL-C by an overall average of approximately 3%, when at least 50g of soy protein was consumed per day. This is a relatively large amount representing half or more of average total protein intake in the US. There is no apparent dose effect. Isoflavones alone do not appear to significantly affect blood lipids. The effect of soy protein on LDL-C is not affected by saturated fat and cholesterol in the diet.
  • Lipoprotein(a) was increased by soy protein in two studies and unaffected in nine others
  • Only three of eight studies of soy protein found modest improvement in menopausal vasomotor symptoms (hot flashes), without benefit from soy isoflavones. Clinical trials are insufficient to be conclusive regarding an effect of soy protein on osteoporosis.
  • It is not possible at this time to state a clinical recommendation for the use of soy isoflavones for the treatment or prevention of breast, endometrial or prostate cancers. Research is insufficient to determine whether phytoestrogens (isoflavones) are protective or harmful for breast cancer.
Author Conclusion:
  • A very large amount of soy protein, more than half the daily protein intake, may lower LDL-C by a few percentage points when it replaces dairy protein or a mixture of animal proteins
  • The evidence favors soy protein rather than soy isoflavones as the effective component
  • No beneift is evident on HDL-C, triglycerides, lipoprotein(a) or BP
  • The direct cardiovascular health benefit of soy protein or isoflavone supplemetns is minimal at best
  • Using soy foods to replace foods high in animal protein that contain saturated fat and cholesterol may confer benefits to cardiovascular health.
  • The efficacy and safety of soy isoflavones for preventing or treating caner of the breast, endometriumm and prostate are not esablished and some evidence is cautionary
  • Isoflavone supplements in food or pills is not recommended.
Funding Source:
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:
  • The review of studies divided those that used isoflavones alone and soy protein with and without isoflavones
  • Isoflavones are removed from soy products that are washed with alcohol
  • The major isoflavones found in soybeans ae genistin, daidzin, andglycitin and their abundance vaires greatly in soy products
  • Isoflavone concentations range from approximately 0.6mg to two mg per gram protein
  • Section on review of BP studies is very brief and data is not included, nor is a discussion of quality of studies or method of analysis
  • This review included the Teede (2001), Hermansen (2001) and Jenkins (2002), studies already included in the analysis for this subquestion.
Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? Yes
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? No
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? Yes
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? No
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? ???
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? No
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? No
  10. Was bias due to the review's funding or sponsorship unlikely? Yes