Clinical Trial of Dietary Protein and Blood Pressure: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Trial of Dietary Protein and Blood Pressure (NCT00046566), a randomized na study. The primary outcome is Change From Baseline in Average Systolic Blood Pressure at 8 Weeks.

2. Clinical Question

3. Trial Design

The registry record identifies this as a randomized, triple-masked crossover trial. In a crossover design, participants receive more than one study condition in a sequence, so each participant may contribute measurements under multiple conditions. The listed sequences vary the order of soy protein, milk protein, and carbohydrate. The record does not describe how the randomization sequence was generated or the details of masking beyond the triple-masked designation.

Each listed sequence includes three 8-week phases. Participants received 40 grams daily of soy protein, milk protein, or complex carbohydrate in the corresponding phase. The sequence descriptions show that the order differed: one begins with soy protein, another with milk protein, and another with carbohydrate. Details such as any washout period between phases are not reported in the registry record.

The registry record lists enrollment of 352 and status as completed. It gives the study start as 2002-07 and primary completion as 2008-04. The posted primary outcome summaries list 284 participants for soy protein, 286 for milk protein, and 287 for carbohydrate. These are condition-specific counts in a crossover trial, not a description of three independent parallel groups. The record does not explain the relationship between enrollment and the count available for each condition.

The primary outcome was average systolic blood pressure change at 8 weeks, expressed in mmHg. Serum LDL-cholesterol change at 8 weeks and body weight at 8 weeks are listed as secondary outcomes. Statistical analysis details, including the model used to account for the crossover structure, are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Intervention 1 (8 Weeks)

Intervention 2 (8 Weeks)

Intervention 3 (8 Weeks)

Analysis population for the primary outcome, as defined in the registry: participants took soy protein during three phases

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Change From Baseline in Average Systolic Blood Pressure at 8 Weeks, measured over Every 8 weeks.

The primary endpoint is change from baseline in average systolic blood pressure at 8 weeks, measured in mmHg. For each intervention phase, the change was calculated from averages based on six blood-pressure readings at two 8-week visits and six readings at two baseline visits. Each visit included three readings taken by trained and certified observers masked to group assignment. Participants were seated quietly for 5 minutes before measurement, and readings were taken from the right arm with appropriately sized cuffs. The record also describes instructions to avoid eating, smoking, alcohol, and exercise for at least 30 minutes before measurement.

Change from baseline expresses how the measured outcome moved during the intervention phase relative to that phase’s baseline. Systolic blood pressure is the specific blood-pressure component selected as the primary measure in this trial. Averaging multiple readings can reduce the influence of short-term measurement variation; that is a general measurement principle, not evidence about how much variation was reduced in this study.

The outcome is reported as a mean with a 95% confidence interval. The registry record does not report a direct contrast between the intervention conditions, so the endpoint summaries describe change within each condition rather than the estimated difference in change between conditions.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is continuous: systolic blood pressure is recorded on a numeric scale, and the primary result is a mean change. A mean summarizes the average direction and size of observed change in a condition. Because a mean alone does not communicate how uncertain it is, the registry record also gives a 95% confidence interval for each condition-specific estimate.

What does a confidence interval convey?

In general, a confidence interval expresses the precision of an estimate under a specified statistical procedure and its assumptions. A narrower interval indicates greater precision than a wider interval, all else equal. The interval does not show the distribution of individual participants’ changes, and it is not a range containing every participant’s result. Nor does a confidence interval for a condition-specific mean answer the same question as a confidence interval for the difference between two conditions.

For the posted results, the mean change and interval are reported separately for soy protein, milk protein, and carbohydrate. The values are -1.5 with an interval from -2.4 to -0.6, -1.8 with an interval from -2.7 to -1.0, and 0.5 with an interval from -0.4 to 1.3, respectively. The position of an interval relative to zero can describe whether the interval includes no mean change for that condition. It does not test whether the mean change differs between conditions. That requires an estimated contrast and its uncertainty, neither of which is reported in the registry record.

Why does the crossover design matter?

In general, a crossover trial collects outcome information from participants under multiple conditions. Observations from the same participant can be correlated, so an analysis may need to account for that within-participant relationship. The listed sequences indicate differing orders of soy protein, milk protein, and carbohydrate. The registry record does not report the statistical model used, whether period or sequence effects were considered, or how any carryover from one phase to another was assessed. It also does not report whether there was a washout period.

Because the posted results are condition-specific summaries, they do not reveal the within-participant covariance or the paired differences. Those details matter for estimating a comparison in a crossover study. The number of participants contributing to a condition-specific summary does not, by itself, reveal how many complete sets of measurements were available across all conditions or how the comparative analysis would have been carried out.

How should the change score be understood?

The registry describes the endpoint as the mean of six blood-pressure values from two visits during an intervention phase minus the mean of six values from two baseline visits within that phase. At each visit, three readings were taken. In general, averaging repeated readings can make a summary less dependent on any single measurement. The record gives the measurement procedures, including observer masking and participant preparation, but does not report measurement reliability or the distribution of individual changes.

A change score uses a baseline reference, whereas a final-value analysis would focus on the measurement at follow-up. The registry record specifies change from baseline; it does not report whether other analytic approaches were also used. The reported means are therefore interpreted as changes under the stated definition, not as final systolic blood-pressure values.

What cannot be inferred from the posted analysis?

The record reports no analysis count and does not post a two-condition comparison for the continuous primary endpoint. It also does not report a statistical model, a p-value, adjustments for multiple outcomes, or details of handling missing observations. As a result, the posted summaries support descriptions of the estimated mean changes and their confidence intervals, but do not establish a comparative effect or indicate how the investigators accounted for the crossover structure.

General statistical interpretation also depends on assumptions such as an appropriate analysis model and valid measurement and missing-data handling. Those assumptions cannot be evaluated from the posted summary estimates alone. No sample-size justification or interim-analysis plan is reported in the registry record. Without those details, the confidence intervals are the most direct posted indication of precision, while the planned design characteristics and analysis procedures remain unclear.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome, change from baseline in average systolic blood pressure at 8 weeks. It also lists two secondary outcomes: change from baseline in serum LDL-cholesterol at 8 weeks and body weight at 8 weeks. The record does not report whether the investigators adjusted for multiple outcomes or comparisons, or how the primary and secondary outcomes were prioritized in any statistical testing strategy. Without that information, the implications of examining several outcomes cannot be assessed from the registry record.

The record gives no analysis count and does not post a comparative analysis for the primary continuous outcome. A statistical analysis plan, including any prespecified hypotheses, model specifications, or rules for handling multiple comparisons, is not reported in the registry record. The absence of those details means the posted means and confidence intervals should not be treated as a complete account of the planned analysis.

Missing-data procedures and analysis populations are also not reported in the registry record. The overall enrollment is 352, while the primary outcome summaries list condition-specific counts of 284, 286, and 287. The record does not explain the reasons for those counts, whether participants contributed to all intervention phases, or how incomplete measurements were handled. It does not state whether the results represent all randomized participants, participants with available measurements, or another defined analysis population.

In general, missing observations can affect both the precision and interpretation of an estimate, depending on why they are missing and how they are handled. The posted counts alone do not establish the pattern or consequences of missing data. No imputation method, sensitivity analysis, or other missing-data approach is reported in the registry record.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry record lists zero serious adverse events and zero deaths for soy protein supplementation, milk protein supplementation, and carbohydrate supplementation. It also lists zero other adverse events for each condition. The corresponding numbers at risk are 284, 286, and 287 for the three conditions, respectively. These are the adverse-event figures posted in the record.

Zero events recorded in a condition does not establish that the condition has no risk. It means that the registry record reports no events in the stated category among the listed number at risk. Such counts do not describe events that were not collected, reported, or classified in the registry entry. The record does not list any serious adverse event terms or give narrative details about safety monitoring, event definitions, or follow-up for adverse events.

Because the trial used a crossover design, condition-specific counts should be read as summaries associated with each condition, not automatically as counts from independent parallel groups. The record does not explain whether participants with exposure to more than one condition contributed to each condition’s at-risk count. The adverse-event figures are descriptive registry entries and do not provide a comparative safety analysis.

12. What the Result Does, and Does Not, Mean

The posted results describe mean changes in average systolic blood pressure during the soy protein, milk protein, and carbohydrate phases. The soy and milk condition means are negative, while the carbohydrate mean is positive. Their 95% confidence intervals communicate uncertainty around these condition-specific mean estimates. This is what the registry record’s primary outcome summaries directly show.

They do not, on their own, establish whether the changes differ between conditions. A comparison requires an estimate of the between-condition contrast and an uncertainty measure that takes account of the crossover design. Neither is posted for the primary continuous outcome. It would therefore be inappropriate to interpret differences between the displayed condition means as a formal comparative result or to claim that one supplement produced a greater change than another based only on these summaries.

The posted information also does not show whether the findings apply to people beyond the study participants. The registry record gives limited detail about eligibility and does not describe participant characteristics in the primary outcome summary. It does not report adherence, missing-data handling, the statistical model, or the treatment of phase and sequence effects. Those omissions limit interpretation of how the estimates were obtained and to whom they may apply.

In general, a trial result is not a treatment recommendation. The record concerns a defined set of dietary supplement phases and a blood-pressure outcome measured using a stated procedure. It does not establish effects on other health outcomes. The secondary outcomes listed are serum LDL-cholesterol change and body weight, but their results are not included in the registry entries for this record.

The appropriate statistical reading is therefore narrow: the registry record reports condition-specific mean changes and confidence intervals, along with adverse-event counts. It does not report the comparative analysis needed to establish differences among conditions, and it does not provide enough analysis detail to assess all assumptions or the handling of incomplete data.

13. Why This Trial Matters Statistically

This trial is statistically notable because its crossover structure affects how condition-specific results should be interpreted. Participants received conditions in different sequences, so measurements under the conditions may be linked within the same person. In general, a comparative analysis of crossover data should account for that relationship. Separate means and confidence intervals do not reveal the paired comparison or its precision.

The endpoint also uses repeated blood-pressure readings at baseline and during each intervention phase. The record gives a detailed measurement definition, including the number of readings and the masked observers. That detail helps explain what the reported change represents, even though the statistical model used to analyze the repeated observations is not reported.

The posted condition-specific confidence intervals make precision visible for each mean change, but they should not be mistaken for uncertainty around a contrast between supplements. This distinction is broadly important in clinical research: two estimates can each have their own interval, while a direct comparison requires its own estimate and uncertainty calculation. The registry record does not post that comparative result.

The record also illustrates why enrollment, outcome counts, and analysis populations should be distinguished. It lists enrollment of 352 and larger condition-specific counts across the three outcomes summaries than might be expected if each condition were a separate parallel arm. In a crossover study, participants can contribute observations under multiple conditions; the record does not explain the counts or identify the analysis population. That makes transparent reporting of participant flow and analysis methods especially useful.

Finally, registry results can be informative while still leaving important statistical questions unresolved. Here, mean changes, confidence intervals, condition-specific counts, and adverse-event entries are posted, but the comparative model, missing-data methods, multiplicity approach, and sample-size justification are not reported in the registry record.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several trial-specific details needed to assess the results are not reported in the registry record. Although the design is identified as a randomized, triple-masked crossover, the randomization procedure and the identities of those masked are not described. The sequence descriptions show different orders of the three conditions, but do not specify whether there was a washout period between phases. Period effects and carryover are relevant general considerations in crossover designs; the record does not state how they were assessed or handled.

The primary endpoint summary gives condition-specific means, confidence intervals, and counts, but no direct comparison between conditions. It also does not identify the statistical model or report whether within-participant correlation was incorporated. No analysis population is defined, and the registry record does not explain the relationship between enrollment and condition-specific counts.

Missing-data procedures, adherence information, and participant characteristics are not reported in the registry record. These omissions limit assessment of the available observations and the extent to which the results may generalize beyond the enrolled participants. The record also does not report a sample-size justification, interim analyses, or a multiplicity strategy. These limitations concern the information available in the registry entry; they do not establish what was or was not done outside that record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Clinical Trial of Dietary Protein and Blood Pressure — NCT00046566.
• Registry record last updated 2017-07-24; status last verified 2017-04.
• Results first posted 2017-07-24.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record identifies NCT00046566 as a completed, randomized, triple-masked crossover study sponsored by Tulane University. Its title is “Clinical Trial of Dietary Protein and Blood Pressure.” Enrollment is listed as 352, with a start date of 2002-07 and primary completion in 2008-04.

The primary outcome is change from baseline in average systolic blood pressure at 8 weeks, reported as a mean in mmHg with a 95% confidence interval. The three posted condition-specific summaries are for soy protein, milk protein, and carbohydrate supplementation. The record also lists serum LDL-cholesterol change and body weight as secondary outcomes.

The posted primary outcome results do not include a direct comparison between conditions. Analysis details, missing-data methods, and a sample-size justification are not reported in the registry record. The adverse-event entries list zero serious events, zero other events, and zero deaths for each condition.