This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Dietary Impact on Intestinal Sulfate Metabolism (NCT05333900), a non-randomized na study. The primary outcome is Effect of Short-term (1-week) Plant- and Animal-based Eating Patterns on Hydrogen Sulfide Production.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT05333900 |
| Phase | NA |
| Condition | Healthy Nutrition |
| Allocation | Non-Randomized |
| Design model | Crossover |
| Masking | None (open label) |
| Enrollment | 15 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of Minnesota |
| Results posted | Yes |
2. Clinical Question
Population
The study concerns healthy human volunteers. The registry describes 15 highly motivated healthy volunteers and lists the condition as Healthy Nutrition. The record does not give further eligibility criteria or participant characteristics, so it does not establish how well the group represents other healthy populations.
Intervention
One eating pattern is a low-sulfur-amino-acid diet emphasizing plant-based foods and fat sources. The other is a high-sulfur-amino-acid diet emphasizing animal protein and fat sources. Each intervention is described as lasting 7 days.
Comparator
The diets are the two conditions of a crossover study, with listed sequences of plant-based then animal-based and animal-based then plant-based. Allocation is nonrandomized and masking is absent. The sequences therefore should not be treated as randomized, like-for-like control arms.
Primary question
The primary question is whether short-term plant- and animal-based eating patterns are associated with differences in ex vivo fecal hydrogen sulfide production. The registry describes measuring fecal production after each 1-week pattern, in healthy volunteers. It identifies the outcome as a median with full range, but does not report the observed medians, ranges, or a comparison estimate. Thus, the record establishes what the study set out to measure, not what the measurement showed.
3. Trial Design
The registry describes a completed, nonrandomized crossover pilot study sponsored by the University of Minnesota. The study is listed as phase NA, with enrollment of 15. Its record gives a start date of 2016-12-07 and a primary completion date of 2020-12-31. The overall status is COMPLETED.
The planned dietary conditions differ in sulfur-containing amino acids and in the food patterns used to achieve them. The Low-S diet emphasizes plant-based foods and fat sources; the High-S diet emphasizes animal protein and fat sources. Each is described as a 7-day intervention. The summary calls the study 5 weeks long and specifies a 14-day washout after each intervention, during which participants would eat their typical diets. The registry does not provide further detail about adherence, how typical diets were characterized, or the timing of outcome collection beyond the stated timeframe following the eating patterns.
Two sequences are listed: plant-based then animal-based, and animal-based then plant-based. Although the study is labeled a crossover, allocation is NON RANDOMIZED and masking is NONE. The record does not explain how participants were assigned to sequence or whether sequence order was balanced. Because the dietary sequences are not randomized, a difference between listed groups would not by itself isolate a diet effect from differences associated with sequence assignment. The record itself flags that the arms are not a like-for-like control comparison.
A crossover design can use each participant’s measurements under both conditions to examine within-person change. That general advantage depends on appropriate measurement and analysis; the registry record does not report whether a paired analysis was used, how period or sequence effects were handled, or how washout was evaluated. Those details matter when interpreting any comparison from a crossover study.
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.
Overall Study
| Stage | Plant-based Then Animal Based | Animal-based Then Plant Based |
|---|---|---|
| STARTED | 7 | 8 |
| COMPLETED | 6 | 5 |
| NOT COMPLETED | 1 | 3 |
Reasons for not completing this period:
| Reason | Plant-based Then Animal Based | Animal-based Then Plant Based |
|---|---|---|
| Protocol Violation | 0 | 1 |
| Withdrawal by Subject | 0 | 1 |
| COVID-19 Pandemic | 1 | 1 |
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.
| Characteristic | Unit | Plant-based Then Animal Based | Animal-based Then Plant Based | Total |
|---|---|---|---|---|
| Participants analysed | 7 | 8 | 15 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 6 | 8 | 14 |
| Age, Categorical: >=65 years | Participants | 1 | 0 | 1 |
| Sex: Female, Male: Female | Participants | 4 | 6 | 10 |
| Sex: Female, Male: Male | Participants | 3 | 2 | 5 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 1 | 0 | 1 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 1 | 1 | 2 |
| Race (NIH/OMB): White | Participants | 5 | 7 | 12 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
6. Primary Endpoint
The registry lists the primary outcome as Effect of Short-term (1-week) Plant- and Animal-based Eating Patterns on Hydrogen Sulfide Production, measured over Following 1-week of plant- and animal-based eating patterns.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Full Range |
| Unit | ppm hydrogen sulfide gas |
| Endpoint classification | not reduced to a single comparison |
The primary outcome concerns ex vivo fecal hydrogen sulfide production after short-term plant- and animal-based eating patterns. The registry describes collecting fecal material and measuring hydrogen sulfide production outside the body. It states that the measurement is in ppm per gram of dry stool in the description, while the listed unit is ppm hydrogen sulfide gas. The registry does not explain this difference in unit wording.
The outcome is specified as a median with full range. In general, the median describes the center of observed measurements without requiring a symmetric distribution, while the full range describes the lowest and highest observations. A median and range can be useful when measurements are skewed or when a pilot study aims to describe variability as well as a typical value. They do not, on their own, quantify uncertainty in a between-diet effect; an interval estimate or an appropriate comparison analysis would be needed for that purpose.
Ex vivo production is a laboratory measure of fecal hydrogen sulfide generation under the measurement conditions. It is not itself a direct measure of symptoms, clinical outcomes, or health benefit. The registry identifies the measurement and its timeframe but does not report the observed values, the laboratory protocol, or a statistical estimate comparing the dietary conditions.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The record gives the study question, design, and primary outcome definition, but it does not report the observed endpoint data. In particular, no median, full range, between-condition estimate, confidence interval, or p-value is reported in the registry record. There is consequently no posted statistical result from which to describe the direction, size, or precision of a difference in fecal hydrogen sulfide production.
The primary outcome is described as a median and full range following the 1-week eating patterns. These summaries would show the central observation and spread in each condition, but a comparison also requires a clearly defined contrast and a method that reflects the crossover structure. The registry lists no analysis records. It does not state whether the analysis compared measurements within participants, compared sequence groups, or used another approach. It also does not report adjustments for period, sequence, or carryover effects. These omissions prevent a reader from reconstructing how the primary question was statistically addressed.
The nonrandomized allocation is important. In general, random assignment can reduce systematic differences between groups, while nonrandom assignment can leave differences related to sequence or participant selection entangled with the condition being compared. In a crossover, order can also matter: an outcome after one diet may depend on the preceding period or on time-related changes. A washout is part of the stated design, but the registry does not report evidence that it eliminated carryover or the method used to assess it. This does not demonstrate that carryover occurred; it means the record does not resolve the issue.
The listed enrollment is 15, and the study is described as a pilot. That context supports reading the work primarily as a small-scale investigation of a dietary manipulation and laboratory endpoint, rather than as definitive evidence about clinical outcomes. The registry does not report a sample-size justification or the precision anticipated for the endpoint. No inferential conclusion can be drawn from enrollment alone.
Planning illustrations may use the observed effect as an input, but the registry record does not provide the outcome estimates or numerical planning results needed to assess those illustrations. Any such sample-size values are planning scenarios under stated assumptions, not observed power and not evidence that the study had a particular probability of detecting an effect. The assumptions described include a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; their relevance to a nonrandomized crossover design is not established in the record.
The narrowest defensible interpretation is therefore descriptive: the study was designed to measure ex vivo fecal hydrogen sulfide production after two short dietary patterns in healthy volunteers. The registry does not report whether those measurements differed or how precisely any difference was estimated. It also does not report clinical outcomes, so the laboratory endpoint should not be translated into a claim about health effects.
9. Statistical Methods Explained
The registry identifies a primary outcome measure but lists no analysis records. Understanding the intended statistical quantities is still useful, provided general statistical principles are kept separate from what this study actually reports. The following explanations are general; they do not establish which analyses the investigators conducted.
What does a median with full range describe?
A median is the middle of the ordered observations. It is often useful when data may be skewed or influenced by extreme observations because it is less sensitive to extremes than the arithmetic mean. The full range gives the minimum and maximum observed values and communicates the span of the data. It can also be sensitive to extreme observations and does not show how densely observations cluster within the range.
For this outcome, separate medians and ranges would describe the distribution of measured fecal hydrogen sulfide production under each dietary condition. They would not, by themselves, answer whether the conditions differ. A comparison requires defining the contrast and using a statistical method appropriate to the design and data. The registry does not report the observed summaries or the comparison method.
Why does the crossover structure matter?
In general, a crossover study measures participants under multiple conditions, so observations from the same person are related rather than independent. A paired analysis can account for this relationship by focusing on each participant’s change between conditions. Treating related observations as independent may misrepresent uncertainty. However, the record does not say that a paired analysis was performed or describe the unit of analysis. The fact that the study is labeled CROSSOVER does not establish the analysis used.
Crossover designs can also be affected by period and sequence. Period effects are changes associated with when a condition occurs; sequence effects are differences associated with the order of conditions. Carryover refers to an effect of an earlier condition persisting into a later period. The described 14-day washout is part of the planned procedure, but a washout period alone does not show whether carryover was absent. The registry does not report analyses or checks addressing these possibilities.
Why does nonrandomized allocation matter?
Randomization is a method for assigning participants to conditions by chance. In general, it helps protect a comparison from systematic baseline differences, though it does not guarantee that all differences disappear. This study is recorded as NON RANDOMIZED. The record lists two dietary sequences but does not explain assignment procedures or report characteristics by sequence. If sequence assignment was related to participant characteristics or other factors, those factors could complicate interpretation. The registry explicitly notes that the arms are not a like-for-like control comparison.
Masking is listed as NONE. For a dietary intervention, participants may be aware of the diet they are following; the record does not describe whether outcome assessors or laboratory staff were masked. In general, masking can limit the influence of expectations or knowledge of assignment on some stages of measurement and assessment. Its absence or use at particular stages cannot be inferred beyond the registry’s masking entry.
What do confidence intervals and significance tests mean?
In general, a confidence interval expresses the uncertainty around an estimated quantity under a specified statistical model. A narrow interval indicates greater precision than a wide interval, while an interval spanning values compatible with different conclusions can leave the comparison uncertain. A p-value measures how unusual the data would be under a specified null model; it does not measure the size or clinical importance of an effect. Neither an interval nor a p-value is reported for the primary outcome in the registry record.
These concepts cannot substitute for a reported estimate. Without outcome data and an analysis description, readers cannot assess the estimated contrast, its uncertainty, or whether assumptions were reasonable. The record also does not state a significance threshold for the trial’s own analysis.
Why can over-dispersion matter?
As a general statistical point, over-dispersion occurs when the variability in data is greater than a model expects. If a model assumes less variability than is present, its standard errors can be too small and its uncertainty estimates misleading. This issue is relevant to some count and rate outcomes, but the registry describes a continuous laboratory measurement summarized by a median and range. It does not report a model or identify over-dispersion as an issue in this study; no claim about its presence or treatment is warranted.
The sample-size assumptions described in the record refer to planning illustrations using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. These are planning assumptions, not a report of the trial’s own design justification or analysis. Sample-size illustrations are not observed power. The registry does not report a sample-size justification, the numerical illustration results, or whether these assumptions match an analysis appropriate to the crossover design.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome measure: ex vivo fecal hydrogen sulfide production following the short-term dietary patterns. It does not report a multiplicity strategy, such as an adjustment for testing multiple outcomes or comparisons. The absence of a reported strategy does not establish that no other analyses were conducted; it means the registry record does not describe how multiplicity was handled. The number of analysis records is listed as zero.
Missing-data methods and analysis populations are not reported in the registry record. It does not state how many participants contributed measurements under each condition, whether any measurements were unavailable, how missing observations were handled, or whether the analysis included all enrolled participants or a subset. The stated enrollment of 15 should not be assumed to equal the number analyzed for the endpoint.
The record also does not report an interim-analysis plan, stopping rules, or a statistical analysis plan. These details matter because prespecified methods clarify how outcomes, missing observations, and multiple comparisons were to be handled. Without them, it is not possible to determine whether the posted analysis followed an intended plan. The record’s completed status describes trial status, not the completeness or analytic handling of endpoint data.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Plant-based Diet | 0 | 15 | 0.0% |
| Animal-based Diet | 0 | 15 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Plant-based Diet | 0 of 15 |
| Animal-based Diet | 0 of 15 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Plant-based Diet | 0 of 15 |
| Animal-based Diet | 0 of 15 |
The registry lists serious adverse event and other adverse event figures separately for the Plant-based Diet and Animal-based Diet groups. Each listed group has 15 participants at risk and records 0 serious adverse events, 0 other adverse events, and 0 deaths. These are the figures recorded for the groups; they should not be added across groups to infer a count of distinct participants, because the study is a crossover and the groups may reflect conditions experienced by the same participants.
Zero recorded events means the registry reports none in those categories during the reported safety accounting. It does not establish that no symptoms or events of any kind occurred, and the record does not provide further detail about event collection, observation periods, or thresholds for recording an event. No serious adverse event terms are listed. These figures describe safety reporting in the registry and do not address the primary laboratory endpoint or establish a clinical benefit or harm.
12. What the Result Does, and Does Not, Mean
This study addresses a specific biological measurement: ex vivo fecal hydrogen sulfide production after short-term dietary patterns that differ in sulfur-containing amino acids and food sources. Its crossover pilot design makes it a preliminary investigation of that question in healthy volunteers. The registry’s description tells readers what was planned and how the diets were characterized, but it does not provide the observed outcome values or an inferential comparison.
Accordingly, the record does not establish whether the Low-S and High-S diets were associated with different measured production, the magnitude or direction of any difference, or the precision of an estimate. It also does not report a statistical analysis of the outcome. The absence of those results from the registry record should not be interpreted as evidence that the diets had the same effect or that a difference was absent.
The endpoint is a laboratory measure, not a direct clinical outcome. Even a reported difference in this measure would not, by itself, establish a difference in symptoms, disease risk, or health status. The record describes healthy volunteers and does not report results for other populations. Nor does it provide enough information to assess whether sequence effects, period effects, or carryover were addressed.
The study’s nonrandomized allocation further limits how a comparison between its listed sequences could be interpreted. The crossover label and stated washout do not remove the need to know how sequence assignment and repeated measurements were handled. Because those methods are not reported, the registry record supports a description of the research question and design, not a causal conclusion about either diet.
For readers, the central distinction is between an endpoint being specified and an outcome being reported. The primary endpoint is clearly described, but its numerical findings and analysis are not reported in the registry record. No conclusion about an effect, its statistical significance, or its practical importance can be drawn from the available record.
13. Why This Trial Matters Statistically
This trial is statistically instructive because it combines a crossover structure with nonrandomized sequence allocation. Crossover studies can make within-person comparisons, which may reduce the influence of stable differences between participants. That potential advantage depends on collecting comparable measurements under each condition and analyzing their dependence appropriately. The registry does not report whether the analysis used within-person comparisons, so the design label alone cannot establish that this advantage was realized.
Order and time are especially relevant in a crossover. The two listed sequences make the order of the dietary patterns part of the design, while the stated washout is intended to separate intervention periods. General statistical reasoning highlights the need to consider period and carryover effects, but the registry does not say whether these were assessed. Nonrandomized allocation adds another concern: sequence groups may differ for reasons other than the dietary order itself.
The endpoint also illustrates the distinction between descriptive summaries and comparative inference. A median and full range can describe measurements, but they do not convey the precision of a contrast without an appropriate estimate and uncertainty measure. Neither outcome summaries nor an analysis are reported in the registry record. This makes careful separation of planned measurement from reported result essential.
Finally, the study is identified as a pilot with enrollment of 15. Pilot findings can inform later research questions and measurement approaches, but this record does not report enough statistical detail to assess the observed variability, estimate precision, or sample-size rationale. Its value for statistical interpretation lies in the design questions it raises, not in an unreported treatment-effect result.
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.
The registry record has important reporting gaps for evaluating this particular study. It does not report the primary outcome values, their full ranges, a between-condition estimate, confidence intervals, or p-values. It lists no analysis records. As a result, the endpoint’s direction, magnitude, and precision cannot be assessed from the record.
Design details are also limited. Allocation is nonrandomized, but the assignment procedure and reasons for sequence assignment are not described. Masking is listed as none, without specifying which people involved in measurement or analysis knew the condition. The record does not say how adherence to the diets was assessed, how the typical diet during washout was characterized, or whether period, sequence, or carryover effects were evaluated.
The primary endpoint’s unit wording differs between the listed unit and the outcome description: the former says ppm hydrogen sulfide gas, while the latter describes ppm per gram of dry stool. The record does not clarify that wording. The outcome is an ex vivo laboratory measure in healthy volunteers, so the record does not support conclusions about clinical outcomes or other populations.
Although sample-size planning assumptions are described, the registry does not report the numerical planning results or a trial-specific sample-size justification. It also does not report missing-data handling, analysis populations, multiplicity procedures, or an interim-analysis plan. These are limitations of what can be evaluated from the registry record; they do not establish what procedures may have been used outside the record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Dietary Impact on Intestinal Sulfate Metabolism — NCT05333900.
- Registry record last updated 2023-12-05; status last verified 2023-12.
- Results first posted 2023-12-05.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
NCT05333900, titled Dietary Impact on Intestinal Sulfate Metabolism, is recorded as a completed, nonrandomized crossover pilot sponsored by the University of Minnesota. Enrollment is listed as 15; the study began on 2016-12-07, with primary completion on 2020-12-31. The registry describes two 7-day dietary patterns, one low and one high in sulfur-containing amino acids, with a 14-day washout after each intervention.
The primary outcome is ex vivo fecal hydrogen sulfide production, summarized as a median and full range. The registry does not report the outcome values or statistical analyses. It also does not report the analysis population, missing-data methods, or multiplicity procedures. Safety entries list zero serious adverse events, zero other adverse events, and zero deaths for each dietary group. The record supports a description of the study design and planned measurement, but not a conclusion about an observed dietary effect.