DLM: Soy (2001)

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

To examine the relationship between soy protein consumption and serum lipids concentrations in humans.

Inclusion Criteria:
  1. used isolated soy protein or textured soy protein
  2. RCT with cross-over or parallel design
  3. Included baseline values.
Exclusion Criteria:
  1. No control group
  2. Used several sources of vegetable protein
  3. Used whole soybeans instead of soy protein
  4. No base-line values available
Description of Study Protocol:

Conducted statistical test of homogeneity and because of the substantial variability between observations, a random effects model was used.

Data Collection Summary:

Subgroup analyses: changes in serum lipid concentrations in relation to

  • lnitial values,
  • types of soy protein used
  • amount of soy protein ingested
  • type of diet
  • age group of subjects
  • similarity of control and soy-containing diets

Meta-analysis: estimate of the principal effect defined as the mean difference between the change in lipid concentration when the subjects ingested the soy-containing diet and the change when they ingested the control diet



Description of Actual Data Sample:

Meta-analysis of 38 articles of primary reports

29 articles met the study criteria.

Most studies used random assignment with crossover design.


Summary of Results:

Diet composition: (number of studies)

20 - isolated soy protein

15 - textured soy protein

3 - isolated soy + textured soy protein.

Soy protein mean 47 g/d (range17-124 g/d)

In 14 studies (37%) intake was <31 g/d

19 studies had control and soy-containing diets similar with respect to dietary fat, cholesterol, and weight change.

Ingestion of soy protein associated with the following net changes in serum lipid concentrations from the concentrations reached with the control diet:

T cholesterol: decrease of 23.2 mg/dl (95% CI, 13.5-32.9 mg/dl) or 9.3%.

LDL chol: decrease of 21.7 mg/dl (95% CI, 11.2-31.7 mg/dl) or 12.9%,

TG: decrease of 13.3 mg/dl (95% CI, 0.3 – 25.7 mg/dl) or 10.5%.

The ingestion of soy protein was associated with a nonsignificant 2.4%  in HDL cholesterol.

The changes in serum cholesterol and LDL-cholesterol concentrations were directly related to the initial serum cholesterol concentration (P<0.001).

Author Conclusion:

We found that the consumption of soy protein rather than animal protein significantly decreases serum concentrations of total cholesterol, LDL cholesterol, and TG.

The decreases were strongly related to the subjects' initial serum cholesterol concentrations.

Funding Source:
Protein Technologies International
Food Company:
University/Hospital: Veterans Affairs Medical Center and Dept of Behavioral Science, College of Medicine, University of Kentucky
Reviewer Comments:
Well-defined criteria for including study for analysis.
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? No
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? N/A
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  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? Yes
  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? Yes
  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? No