Optimizing Protein Patterns for Skeletal Muscle Preservation and Sleep in the Medical Management of Parkinson Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Optimizing Protein Patterns for Skeletal Muscle Preservation and Sleep in the Medical Management of Parkinson Disease (NCT05437640), a randomized na study. The primary outcome is Change in Markers of Skeletal Muscle Metabolism GDF15.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, single-masked, crossover study of two behavioral dietary interventions. The interventions were the Protein Redistribution Diet and the Protein Consistent Diet. Participants could be randomized to follow either diet first and then the other, so the planned design included both possible sequences. The identity of the person or group kept masked is not reported in the registry record.

The study enrolled 12 participants and is listed as completed. The record gives a start date of 2022-10-01 and a primary completion date of 2024-11-25. It identifies Parkinson disease as the condition under study and lists the phase as NA. The sponsor is the University of Alabama at Birmingham.

The primary outcome is change in serum GDF15 from baseline to five weeks. The registry record also lists change in physical activity and change in total Parkinson symptoms as secondary outcomes. Seven outcome measures are listed, while two secondary outcomes are posted in the registry record; the record does not explain how the remaining measures relate to those entries. No statistical analyses are listed.

A crossover design exposes participants to both interventions, with sequence randomized. In general, this can allow comparisons that account for stable differences between participants. The registry record does not report the duration of each diet period, any washout interval, or the methods used to address period, sequence, or carryover effects. These omissions limit how fully the posted group summaries can be interpreted as a crossover analysis.

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.

First Intervention (2 weeks)

Washout (1 week)

Reasons for not completing this period:

Second Intervention (2 weeks)

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 in Markers of Skeletal Muscle Metabolism GDF15, measured over Baseline to 5 weeks.

The primary endpoint is titled “Change in Markers of Skeletal Muscle Metabolism GDF15.” It measures serum Growth Differentiation Factor 15 (GDF15), in pg/mL, from baseline to five weeks. GDF15 is the marker named in the registry record; the study summary describes its broader purpose as generating preliminary data on dietary protein patterns and markers of skeletal muscle health and drug efficacy in Parkinson disease.

The endpoint is continuous, and the posted summaries are means with standard deviations. A mean gives the group’s average value, while a standard deviation describes the spread of participant values around that average. The registry record does not provide a detailed rationale for selecting GDF15 or define what size of change would be considered important. It also does not describe whether the posted values are calculated from individual changes, follow-up values, or another specified endpoint calculation beyond the baseline-to-five-weeks timeframe.

For the Protein Consistent Diet, the posted mean is 1134.0 pg/mL, with a standard deviation of 520.0 and 11 participants. For the Protein Redistribution Diet, the mean is 1125.0 pg/mL, with a standard deviation of 582.0 and 11 participants. These summaries describe the endpoint values as posted; they do not alone show how individual participants changed or how those observations were handled in a crossover model.

7. Results Posted in the Registry

• Protein Redistribution Diet: mean 1,125 versus 1,134 on control; difference -9.00 (95% CI -470.22 to 452.22), standardized effect d = -0.02; z-test p = 0.969.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies the primary measure as continuous and summarizes it with a mean and standard deviation. A mean describes the central value of a group. A standard deviation describes how dispersed the individual measurements are around that mean. Neither summary conveys the full distribution, and neither reveals whether observations are skewed or unusually influential.

What the group comparison represents

The posted comparison is a mean difference, with the Protein Consistent Diet as the reference and the Protein Redistribution Diet as the comparison. Its estimate is -9.0 pg/mL. In general, a mean difference expresses the amount by which one group’s average is higher or lower than the other group’s average, in the endpoint’s units. A negative estimate means the posted mean for the redistribution diet is lower than the posted mean for the consistent diet. This is a descriptive direction, not evidence that the difference is real or meaningful.

The p-value is 0.969. In general, a p-value measures how unusual the observed data, or data more extreme, would be under a specified null model. It is not the probability that the null hypothesis is true, nor does it indicate the probability that a result is due to chance. The registry record does not describe a complete statistical analysis plan or the model underlying this comparison. The p-value is therefore read as the unadjusted value posted with the comparison, not as evidence about all possible analyses.

Why the crossover structure matters

In a crossover study, participants receive both interventions in a randomized order. General statistical methods for this design can compare each participant’s outcome under one condition with their outcome under the other condition. This can account for stable participant characteristics that affect both measurements. It also requires attention to the sequence in which interventions were received and to changes over time or residual effects from an earlier period.

The registry record gives the randomized sequences in general terms but does not report the statistical model, whether the comparison used paired observations, how period or sequence effects were handled, or whether carryover was assessed. The group means and standard deviations alone cannot establish those details. The record also does not state how missing observations, if any, were treated. No assumptions about those procedures should be inferred from the crossover label.

What standard deviations and uncertainty contribute

The standard deviations are 520.0 pg/mL for the Protein Consistent Diet and 582.0 pg/mL for the Protein Redistribution Diet. In general, greater variability makes it harder to estimate a group mean or the difference between means precisely, particularly when the number of observations is limited. The posted comparison includes a pooled standard deviation of 551.9 pg/mL. Pooling summarizes variability across the two groups for the comparison; it does not remove uncertainty or resolve the design questions about the crossover.

The reported standard errors are 156.8 for the Protein Consistent Diet and 175.5 for the Protein Redistribution Diet. In general, a standard error describes the sampling uncertainty of an estimate, rather than the spread of individual values. The standard errors are not the same quantity as the standard deviations. The record does not give a confidence interval for each group mean, but it gives one for the mean difference.

Interpretation without a complete analysis plan

The registry lists seven outcome measures, two posted secondary outcomes, and zero analyses. It does not report a statistical analysis plan, adjustment for multiple outcomes, a missing-data method, or the population used for analysis. These items are important to a full appraisal because outcome selection, analytic choices, and missingness can affect reported estimates and uncertainty. Their absence does not show that no such procedures were used; it means they are not reported in the registry record.

The trial is labeled as a pilot study, and its summary says the goal is to generate preliminary data. General pilot-study interpretation emphasizes estimation and feasibility rather than treating a non-significant test as evidence of no effect. The posted mean difference and its interval describe the estimate and its imprecision. The record does not report a prespecified clinically important difference, so the estimate cannot be classified against such a threshold.

10. Confidence Intervals and Precision

The confidence interval for the mean difference extends from -470.2 to 452.2 pg/mL around the estimate of -9.0 pg/mL. A confidence interval gives a range of values compatible with the data under the statistical procedure used. In general, a narrower interval indicates greater precision; a wider interval indicates that the data leave more uncertainty about the underlying difference.

This interval spans zero and includes substantial differences in either direction. The posted estimate is therefore imprecise: the data do not pin down whether the mean is lower or higher under the Protein Redistribution Diet, or how large any difference may be. The confidence interval should not be interpreted as assigning equal probability to every value within it, nor as a guarantee that the true value lies inside it.

The posted group sizes are 11 for each diet, and the reported standard deviations are 520.0 pg/mL and 582.0 pg/mL. In general, limited sample size and variation in measurements contribute to uncertainty. In a crossover study, the precision of a within-participant contrast can also depend on the relationship between observations from the same participant. That relationship is not reported in the registry record, so the group summaries cannot show how much paired information contributed to the interval.

The width of the interval matters alongside the p-value. A large p-value does not mean that the estimate is precise, and an interval that includes zero does not establish equivalence. The registry record does not report an equivalence margin or a threshold for a meaningful GDF15 change. Consequently, the posted result supports a cautious description of uncertainty rather than a definitive conclusion about the size of any difference.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm for 80% power and participants per arm for 90% power. They are not total event counts: the total-events convention applies to time-to-event calculations, while this endpoint is continuous. The planning assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is set to a stated fraction of the observed effect. The trial’s original design assumptions are not reported in the registry record.

For planning at 100% of the observed effect, the figures are 59,024 participants per arm for 80% power and 79,017 participants per arm for 90% power. At 75% of the observed effect, they are 104,932 per arm for 80% power and 140,474 per arm for 90% power. At 50% of the observed effect, they are 236,096 per arm for 80% power and 316,066 per arm for 90% power.

In general, power is the chance that a study will detect an effect of a specified size using a specified test and assumptions. The 80% and 90% columns show the calculated participants per arm associated with those respective planning targets. Higher power generally requires more participants. Smaller effects require more participants to detect than larger effects, which is why the figures increase as the assumed fraction of the observed effect decreases.

These are planning illustrations based on the observed estimate, not observed power. The observed effect is very close to zero, so basing a future design directly on it produces very large planning figures. Those figures should not be mistaken for the enrollment target of this pilot or for the trial’s own sample-size justification.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -9.000; pooled standard deviation σ = 551.871.
2. n = 2 × (1.96 + 0.842)² × 551.871² / -9.000² = 59,024.0, rounded up to 59,024 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -9                      # observed difference in means
sigma <- 551.871361822662                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(5437640)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 59,024 (80% power), 79,017 (90% power)
 75% of observed effect: n per arm = 104,932 (80% power), 140,474 (90% power)
 50% of observed effect: n per arm = 236,096 (80% power), 316,066 (90% power)
power.t.test: 59024.9 
Simulated power at n = 59,024 per arm: 0.802 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists seven outcome measures and identifies two secondary outcomes: change in physical activity and change in total Parkinson symptoms. It also reports zero analyses. The record does not explain which outcomes were analyzed, how the seven measures relate to the posted results, or whether the primary outcome was the only endpoint tested.

When a study evaluates multiple outcomes or performs multiple statistical tests, the chance of at least one apparently noteworthy result can increase. General approaches to multiplicity include prespecifying a primary analysis or adjusting inference across tests. The registry record does not report whether any such approach was planned or used. The posted p-value is described as unadjusted; no multiplicity-adjusted result is reported.

The registry record does not report missing-data counts, reasons for missingness, an imputation method, or a sensitivity analysis. It also does not report the analysis population, such as whether summaries included all randomized participants or only those with usable endpoint measurements. The overall enrollment is 12, whereas the endpoint summaries show 11 participants for each diet. Without an explanation, it is not possible to determine whether that pattern reflects missing observations, the crossover structure, or another reporting choice.

For a crossover design, analysis populations and missing periods can affect how many participants contribute a complete within-person comparison. The record does not state how incomplete participant data were handled or whether observations from only one diet period were used. These details are not minor technicalities: they help define which participants inform the estimate and how uncertainty is calculated. Their absence limits independent assessment of the analysis, but does not establish that data were missing or that a particular method was used.

14. 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.

Most frequent non-serious adverse event terms

The registry reports serious adverse events for 12 participants at risk under each diet. No serious adverse events are listed as affecting participants in either the Protein Consistent Diet group or the Protein Redistribution Diet group. Deaths are reported as zero for both groups.

For other adverse events, 12 participants are listed at risk in each group. The Protein Consistent Diet group has 2 participants affected, and the Protein Redistribution Diet group has 0 affected. The record does not give event terms for these other adverse events, so their nature and severity cannot be described from the posted figures.

These counts are descriptive safety summaries. They do not establish that an intervention caused an event, and the record does not report comparative safety testing or detailed exposure time. With the limited enrollment, absence of reported serious events should not be treated as proof that serious events cannot occur. No serious adverse event terms are listed.

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

The primary result is an uncertain estimate of the difference in mean GDF15 between the two diet patterns over the baseline-to-five-weeks timeframe. The posted mean difference is -9.0 pg/mL, with a confidence interval from -470.2 to 452.2 pg/mL and an unadjusted p-value of 0.969. These statistics show that the estimate is close to zero but imprecise; they do not establish that the diets have identical effects.

The result applies to the endpoint and comparison as posted. GDF15 is a marker of skeletal muscle metabolism in this registry record. The result does not directly demonstrate a change in muscle function, drug efficacy, physical activity, total Parkinson symptoms, or any clinical outcome. Although the study summary mentions muscle health and drug efficacy as motivations, the posted primary endpoint is GDF15, and the record does not give results for the two listed secondary outcomes.

The study is a pilot with an enrollment of 12. It can contribute preliminary information about the observed endpoint values, but its summary estimates are not precise enough to settle the direction or size of a difference. A non-significant p-value does not establish no effect. Conversely, the point estimate alone should not be treated as evidence of a meaningful difference. The record does not report a threshold for clinical importance.

The crossover design means participants could receive both diet patterns in randomized order, but the registry record does not describe the analysis model or how sequence and period features were handled. The endpoint summaries show 11 participants in each diet group, and the record does not explain the relation to total enrollment. These reporting gaps constrain interpretation of the contrast and how broadly it should be generalized.

The appropriate conclusion is narrow: the posted GDF15 comparison is compatible with a range of differences in either direction and is not precise. It neither establishes a benefit nor rules one out, and it should not be used alone to make treatment decisions.

16. Why This Trial Matters Statistically

This trial is statistically informative as an example of the distinction between an estimate and the certainty around it. The mean difference is -9.0 pg/mL, but its confidence interval spans values on both sides of zero and covers a broad range. The point estimate and the interval answer different questions: the estimate gives the observed direction and size, while the interval communicates how uncertain that estimate is.

The pilot framing is also important. The registry summary says the study aims to generate preliminary data about dietary protein patterns, skeletal muscle markers, and drug efficacy in Parkinson disease. Pilot data can help characterize variability and guide future research, but a small study with a wide interval cannot reliably distinguish a small effect from no effect or effects in the other direction. Its value is not limited to a statistically significant finding.

The crossover design illustrates why design labels do not replace analysis details. Randomizing the order of two interventions can support within-participant comparisons, but interpretation depends on how the repeated measurements and sequence are modeled. The registry record does not report those methods. That missing information prevents a reader from determining how the posted comparison used the crossover structure.

The planning figures provide another statistical lesson: sample-size calculations depend strongly on the assumed effect size. Because the observed estimate is close to zero, planning to detect a fraction of that estimate yields very large participant counts. Such figures are calculations under stated assumptions, not a verdict on feasibility or a recommendation for a future study. Any future design would need its own justified target effect and analysis assumptions, which are not reported for this trial.

17. 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 limitations follow from the registry record. The enrollment is 12, while the primary outcome summaries list 11 participants for each diet; no explanation or analysis-population definition is reported. The posted mean difference has a broad confidence interval, so the endpoint estimate is imprecise. The record does not provide participant-level observations or clarify how the crossover structure was incorporated into the comparison.

Important design and analysis details are not reported in the registry record, including the identity of the masked party, the length of each diet period, any washout interval, the handling of period or sequence effects, the statistical analysis plan, and missing-data procedures. The record also does not report an interpretation threshold for a meaningful GDF15 change. These are reporting limitations; their absence does not show that the procedures were not undertaken.

The study lists seven outcome measures, but only two secondary outcomes are identified in the record and zero analyses are listed. Results for the secondary outcomes are not present in the registry entries. The safety summary gives counts but not terms for the other adverse events. The limited enrollment and short primary outcome timeframe further constrain what can be inferred about uncommon events or outcomes beyond five weeks.

Finally, GDF15 is a marker, not a direct report of muscle function or clinical status. The registry summary describes broader aims, but the posted primary result addresses only the named marker. Conclusions should therefore remain limited to that endpoint and should not be extended to unreported outcomes or longer-term effects.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Optimizing Protein Patterns for Skeletal Muscle Preservation and Sleep in the Medical Management of Parkinson Disease — NCT05437640.
• Registry record last updated 2026-06-22; status last verified 2026-05.
• Results first posted 2025-06-15.
• 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.

21. Record Summary

The record describes a completed randomized, single-masked crossover pilot study sponsored by the University of Alabama at Birmingham. It enrolled 12 people with Parkinson disease and compared the Protein Redistribution Diet with the Protein Consistent Diet. The primary outcome was change in serum GDF15 from baseline to five weeks.

The posted means are 1134.0 pg/mL for the Protein Consistent Diet and 1125.0 pg/mL for the Protein Redistribution Diet, with 11 participants in each group. The mean difference is -9.0 pg/mL, with a confidence interval from -470.2 to 452.2 pg/mL and an unadjusted p-value of 0.969. The registry record does not report a statistical analysis plan, analysis population, or details explaining the crossover analysis. The results are preliminary and imprecise; the record does not support conclusions about unreported outcomes or clinical effects.