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 Effect of Spice Consumption on the Microbiome (NCT03676803), a randomized na study. The primary outcome is Change in Microbial Phylum Abundance (% of Total) Between Spice and Placebo.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03676803 |
| Phase | NA |
| Condition | Microbiota |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 31 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of California, Los Angeles |
| Results posted | Yes |
2. Clinical Question
Population
Healthy participants in a free-living population were enrolled. The study concerns the gut microbiome, listed in the registry record under Microbiota. The record states that data from one participant in the spice group and one participant in the placebo group were excluded because of protocol non-compliance.
Intervention
Participants in the mixed-spices group consumed a capsule containing 5 g of mixed spices at culinary dose. The planned intervention period was 2 weeks.
Comparator
The placebo group consumed a capsule containing 5 g of maltodextrin. The registry describes this as the placebo intervention.
Primary question
The study asked whether change in microbial phylum abundance, expressed as a percentage of total bacteria, differed between the mixed-spices and placebo groups after 2 weeks. The registry record does not report one reduced comparison or an effect estimate for this primary outcome.
This is a pilot study of daily spice consumption and the gut microbiome in healthy participants. Its stated motivation was that human intervention studies had examined high-polyphenol fruits and vegetables, while information about spice consumption and the gut microbiome was described as unavailable. A secondary outcome was change from baseline in short-chain fatty acids at 2 weeks. The registry record does not give a single numerical result for either outcome in the information reported for this study. Accordingly, the clinical question can be described, but the size and precision of any between-group difference cannot be assessed from the registry record.
3. Trial Design
The study is registered as completed and is described as a pilot study. It used randomized allocation and a parallel-group model, with single masking. The record does not identify who was masked, so the masking designation alone does not establish whether participants, study staff, outcome assessors, or another group were unaware of assignment.
The registry reports enrollment of 31 participants. The two groups were assigned to daily mixed spices or placebo: the intervention was a capsule containing 5 g of mixed spices at culinary dose, and the placebo capsule contained 5 g of maltodextrin. Participants were described as healthy, and the study was intended to assess the intervention in a free-living population. The primary outcome timeframe was 2 weeks. The listed secondary outcome was change from baseline in short-chain fatty acids at 2 weeks.
Data from one participant in each group were excluded because of non-compliance with the protocol. The registry does not report a complete analysis population or explain how enrollment relates to the number included in each outcome analysis. The planned allocation ratio, randomization procedure, concealment method, detailed masking procedures, and protocol-specific sample-size justification are not reported in the registry record.
The registry lists two outcome measures and four analyses. The primary outcome concerns changes in microbial phylum abundance, expressed as a percentage of total bacteria, and is described using a mean and standard deviation. The record indicates that the primary outcome contains several categories or time points and is not reduced to one comparison. As a result, the design and intended measurement can be described, but a single primary treatment contrast cannot be interpreted from the reported outcome information.
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.
Before assignment: After one week run-in period, thirty-one participants were enrolled and randomized into mixed-spices intervention group and placebo group. All have completed the two-week intervention study.
Overall Study
| Stage | Mixed Spices Intervention Group | Placebo Group |
|---|---|---|
| STARTED | 15 | 16 |
| COMPLETED | 15 | 16 |
| NOT COMPLETED | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: Data from one participant from spice group and one from placebo group were excluded due to non-compliance with the protocol.
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 | Mixed Spices Intervention Group | Placebo Group | Total |
|---|---|---|---|---|
| Participants analysed | 15 | 16 | 31 | |
| Age, Continuous | years | 34.8 (SD 12.2) | 35.6 (SD 13.7) | 35.2 (SD 12.7) |
| Sex: Female, Male: Female | Participants | 11 | 12 | 23 |
| Sex: Female, Male: Male | Participants | 4 | 4 | 8 |
| Race/Ethnicity, Customized: African American | Participants | 3 | 1 | 4 |
| Race/Ethnicity, Customized: White | Participants | 7 | 9 | 16 |
| Race/Ethnicity, Customized: Asian | Participants | 3 | 3 | 6 |
| Race/Ethnicity, Customized: Multi-racial | Participants | 1 | 3 | 4 |
| Race/Ethnicity, Customized: Other | Participants | 1 | 0 | 1 |
| Region of Enrollment: United States | Participants | 15 | 16 | 31 |
| BMI | kg/m^2 | 28.3 (SD 6.8) | 26.7 (SD 4.4) | 27.5 (SD 5.7) |
6. Primary Endpoint
The registry lists the primary outcome as Change in Microbial Phylum Abundance (% of Total) Between Spice and Placebo, measured over 2-weeks.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | percentage of total bacteria |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is change in microbial phylum abundance, expressed as a percentage of total bacteria, compared between the mixed-spices and placebo groups after 2 weeks. A phylum is a broad grouping of microorganisms; measuring its abundance describes the composition of the microbial community rather than an individual participant’s symptoms or a clinical event. The registry specifies that the measure is a continuous outcome summarized by its mean and standard deviation.
General: A change-from-baseline measure describes how an outcome differs from its starting value over the stated follow-up. Expressing abundance as a percentage of total bacteria gives a relative measure of community composition. Such relative measures are distinct from absolute counts: a percentage can change when the measured group changes, when other groups change, or both. This is a general property of relative-abundance measures, not a reported finding from this study.
The comparison is intended to assess whether the average change in microbial phylum abundance differs between participants assigned to the spice capsule and those assigned to placebo. The outcome may be relevant to the study’s microbiome question because it captures composition at the level of microbial phyla. However, the registry record does not report a single reduced result for this endpoint, its numerical estimate, or its uncertainty. It therefore does not establish the direction, size, or precision of a between-group difference.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry describes a randomized pilot comparison of mixed spices with placebo, with microbial phylum abundance as the primary outcome and a 2-week timeframe. This establishes the question the trial was designed to address, but the reported primary-outcome information does not provide a single contrast suitable for interpreting an overall treatment effect. The record explicitly indicates that the primary outcome includes several categories or time points and is not reduced to one comparison.
For that reason, no numerical between-group difference, confidence interval, or test result for the primary outcome is reported in the registry record. The absence of a single displayed estimate should not be mistaken for evidence that the groups were identical, nor does it establish that one group had a greater change. Neither direction nor magnitude can be inferred from the description of the endpoint alone. The same caution applies to the listed secondary outcome, change from baseline in short-chain fatty acids at 2 weeks: a numerical result is not reported in the registry record.
The registry reports enrollment of 31 participants and notes that data from one participant in each group were excluded because of protocol non-compliance. These details indicate that the stated outcome data were subject to exclusions, but the record does not provide the final analysis population for each measure. Nor does it explain how the exclusions were handled in the analyses or whether other observations were missing.
General: An effect estimate describes the observed contrast between groups, while a confidence interval describes the range of values compatible with the data under the analysis assumptions. A test result, when reported, addresses the data’s compatibility with a specified null hypothesis; it does not by itself convey the size or practical relevance of a difference. Here, the registry record does not report a single primary estimate or its uncertainty, so those interpretations cannot be made.
The study is identified as a pilot, and its enrollment should be read as the number enrolled, not as evidence of a particular degree of statistical power. A planning calculation based on an observed effect is not observed power. The registry’s sample-size assumptions describe an illustration using a two-sided significance level of 0.05, equal allocation, a normal approximation, and a stated fraction of an observed effect. Because the primary effect is not reported as one comparison, the assumptions alone cannot establish the trial’s ability to detect a particular difference. The protocol’s own sample-size justification is not reported in the registry record.
The safety counts are also descriptive. No serious adverse events or deaths are listed in either group, while other adverse events are listed for the mixed-spices group and not for placebo. These figures do not provide event types, severity details beyond the serious/non-serious distinction, or a causal assessment. They should be interpreted as registry counts rather than as proof of a safety difference or absence of risk.
9. Statistical Methods Explained
The registry identifies the study as randomized, single-masked, and parallel-group. These design labels describe how participants were assigned and followed, but they do not provide all the details needed to reproduce or fully evaluate the analysis. The specific randomization method, concealment procedures, identity of the masked parties, and statistical analysis plan are not reported in the registry record.
What randomization and a parallel design mean
General: Randomization assigns participants to intervention groups using a chance-based process. Its purpose is to reduce systematic differences between groups at the point of assignment, although it does not guarantee that every participant characteristic will be balanced, particularly in a pilot study. In a parallel-group design, participants remain in their assigned group during the comparison rather than crossing from one intervention to the other. These general features help explain the design labels; the registry does not report the detailed procedures used in this study.
Single masking means that one party or category of parties was masked, but the label does not identify who. Without that detail, readers cannot judge from the registry record how masking may have applied to participants, study personnel, or outcome assessment. The record also does not describe whether masking was maintained throughout the intervention or how it was assessed.
How to understand the continuous outcome
The primary measure is change in microbial phylum abundance as a percentage of total bacteria. The registry identifies the summary parameter as a mean and the measure of dispersion as a standard deviation. General: A mean describes the average value in a group. A standard deviation describes the spread of individual observations around that group average; it is not the same as the uncertainty in the estimated mean or the uncertainty in a between-group effect. A treatment comparison typically needs an estimate of the contrast and a measure of its uncertainty, but neither is reported as one primary comparison in this record.
Because phylum abundance is expressed as a percentage of total bacteria, it is a relative measure. General: Relative-abundance data are constrained by the total: the percentages across categories share a common whole. A change in one category’s percentage may reflect a change in that category, changes elsewhere in the community, or both. This makes the biological meaning of a single percentage change dependent on the wider composition and on the measurement and analysis choices. The registry record does not provide enough detail to evaluate those choices or their consequences.
Why multiple categories and time points matter
The record states that the primary outcome has several categories or time points and is not reduced to one comparison. General: When an outcome includes multiple categories or repeated time points, separate comparisons can raise multiplicity concerns. The more comparisons considered, the greater the chance that at least one result may appear notable by chance if the analyses are interpreted without accounting for the number of comparisons. Prespecified primary contrasts, an appropriate adjustment strategy, or a clear hierarchical analysis can help define how results should be interpreted. The statistical plan and any multiplicity adjustment are not reported in the registry record.
The registry lists two outcome measures and four analyses, but does not describe the analyses in enough detail to identify the specific models, contrasts, or any adjustment for multiple testing. It also does not report a single primary-effect estimate that would allow readers to assess the size and precision of the main contrast. No p-value or confidence interval for that single contrast is reported in the registry record.
Planning calculations and observed results
The stated sample-size assumptions describe a planning illustration: a two-sided significance level of 0.05, equal allocation between the arms, a normal approximation, and an effect to detect expressed as a stated fraction of the observed effect. General: Such calculations explore how a future study might be sized under specified assumptions. They are not observed power, and they do not show that the trial had a particular probability of detecting an effect after its data have been collected. A calculation based on an observed effect is also sensitive to the estimate used as its starting point. The registry record does not report a single primary observed effect for this comparison, and it does not report the protocol’s sample-size justification.
For continuous outcomes, a normal approximation is a mathematical assumption used in some planning or analysis procedures. General: The appropriateness of an approximation depends on the data and analysis context. The registry does not describe diagnostic checks or model details, so those aspects cannot be evaluated from the record.
What the reported exclusions tell us
The registry states that data from one participant in the spice group and one participant in the placebo group were excluded because of protocol non-compliance. This is an explicit exclusion reason, but it does not establish whether all other enrolled participants contributed data to every outcome. General: Excluding participants after randomization can affect interpretation if the excluded participants differ systematically from those retained, or if the reasons for exclusion relate to outcomes. An intention-to-treat analysis generally seeks to retain participants in their assigned groups, while other analysis populations may use different inclusion rules. The registry does not identify the analysis population or report a detailed missing-data strategy, so the implications of the exclusions cannot be resolved from the record.
10. Multiplicity, Missing Data and Analysis Populations
The primary outcome is described as having several categories or time points, and the registry record indicates that it is not reduced to one comparison. This prevents a single primary contrast from being interpreted from the reported information. The registry lists two outcome measures and four analyses, but it does not specify which contrasts were prespecified, how the analyses relate to each outcome, or whether any multiplicity adjustment was used. An adjustment strategy or other plan for controlling interpretation across multiple comparisons is not reported in the registry record.
General: Multiplicity arises when several statistical comparisons are made. If each is interpreted independently, the likelihood of at least one chance finding can increase. Clear specification of the main contrast and a suitable approach to multiple comparisons help readers distinguish the principal question from exploratory analyses. These are general considerations; the record does not report enough analysis detail to determine how multiplicity was addressed in this trial.
For missing data and exclusions, the registry states that one participant from each group was excluded from the data because of protocol non-compliance. It does not report whether other data were missing, whether the excluded participants contributed to any other outcomes, or how incomplete outcome measurements were handled. The analysis population for the primary and secondary outcomes is not reported in the registry record. A named intention-to-treat, per-protocol, or other analysis population is not reported, and the registry does not describe imputation or sensitivity analyses. These omissions limit assessment of how exclusions and missing observations may affect the estimates.
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 |
|---|---|---|---|
| Mixed Spices Intervention Group | 0 | 15 | 0.0% |
| Placebo Group | 0 | 16 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Mixed Spices Intervention Group | 0 of 15 |
| Placebo Group | 0 of 16 |
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 |
|---|---|
| Mixed Spices Intervention Group | 2 of 15 |
| Placebo Group | 0 of 16 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Mixed Spices Intervention Group | Placebo Group |
|---|---|---|---|
| stomach discomfort | Gastrointestinal disorders | 2 of 15 | 0 of 16 |
The registry lists zero serious adverse events in the mixed-spices group among 15 participants at risk and zero in the placebo group among 16 participants at risk. Deaths are listed as zero in both groups. For other adverse events, the registry lists 2 among 15 participants at risk in the mixed-spices group and 0 among 16 participants at risk in the placebo group.
These are event counts as recorded, not a statistical comparison. The registry record does not identify the types of other adverse events, their timing, severity, duration, or whether investigators considered them related to the intervention. It also does not report a formal safety analysis or uncertainty around the counts. A zero count in this study does not demonstrate that an event cannot occur, and the difference in recorded counts does not by itself establish that the intervention caused an event. The figures should therefore be read as descriptive registry information for the groups and participants at risk, not as a definitive comparison of safety.
12. What the Result Does, and Does Not, Mean
The record establishes that a randomized pilot study compared daily capsules containing 5 g of mixed spices with placebo capsules containing 5 g of maltodextrin in healthy participants. Its primary question concerned change in microbial phylum abundance as a percentage of total bacteria after 2 weeks. It also lists change from baseline in short-chain fatty acids at 2 weeks as a secondary outcome.
What the registry record does not establish is the direction or size of a primary between-group effect. The primary endpoint is not reduced to one comparison, and a single estimate with its uncertainty is not reported in the registry record. Thus, the data described in the record cannot support a conclusion that microbial abundance increased, decreased, or remained similar between groups. The same caution applies to the secondary outcome, for which a numerical result is not reported.
This distinction matters because a study question and a study result are not interchangeable. Describing an endpoint tells readers what investigators intended to measure; it does not reveal what the measurements showed. Likewise, randomized allocation describes the design, but does not substitute for outcome estimates or an account of how the data were analyzed.
The enrollment of 31 and the exclusions for protocol non-compliance provide context for the study, but do not establish the number analyzed for each endpoint or the precision of any estimate. The safety counts describe recorded events, but lack event details and a causal assessment. The pilot designation and planning assumptions do not demonstrate observed power or settle whether an effect was present.
General: Statistical evidence is most interpretable when the estimated contrast, uncertainty, analysis population, and analysis plan are clear. Without a single primary estimate and its precision, neither evidence for a difference nor evidence that a meaningful difference is absent can be assessed from the registry record. The findings therefore cannot be used to make a treatment recommendation. They describe a research question and design, while leaving the primary numerical result unresolved in the registered information.
13. Why This Trial Matters Statistically
This trial is statistically informative as an example of why a clearly stated research question and a reportable treatment contrast are both needed. The registry identifies a population, two randomized groups, a 2-week intervention period, and a continuous microbiome outcome. Those details define the broad comparison. However, because the primary outcome includes several categories or time points and is not reduced to one comparison, readers do not receive one estimate that directly answers the overall question.
For a pilot study, the focus may include learning about feasibility or measurement, but the registry record does not report a specific feasibility objective or protocol justification. What can be said from the record is that enrollment was 31 and that one participant in each group was excluded for protocol non-compliance. These details make it especially important to know the analysis population, the handling of missing measurements, and the precision of the outcome estimates. Those elements are not reported in sufficient detail to assess them.
The endpoint also illustrates the interpretive challenges of relative-abundance data. Expressing a phylum as a percentage of total bacteria provides information about community composition, but does not by itself show absolute changes in microbial quantity. General: A percentage-based outcome is constrained by the total and can shift when other components change. Analysis choices and a clear definition of the main contrast are therefore important for interpreting such measures.
Finally, the record distinguishes planned sample-size assumptions from observed evidence. General: Planning illustrations can help frame future research under explicit assumptions, but cannot replace an observed estimate and its uncertainty. Since a single primary effect is not reported, the registry record cannot show how precisely the primary question was answered. This is a statistical reporting limitation, not evidence for or against an intervention effect.
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 principal limitation for interpreting the trial is that the registry record does not report a single reduced comparison for the primary outcome. It describes microbial phylum abundance as a percentage of total bacteria, measured after 2 weeks, but notes that the outcome has several categories or time points. A single effect estimate, confidence interval, or test result for the primary contrast is not reported in the registry record. The direction, magnitude, and precision of the primary comparison therefore cannot be evaluated.
The registry identifies the study as a pilot and reports enrollment of 31 participants, but does not report a protocol-specific sample-size justification. The listed planning assumptions are not a substitute for such a justification or for observed results. The number analyzed for each outcome is not reported, and the registry notes exclusions for protocol non-compliance without describing the full analysis population or the handling of other possible missing data.
Details needed to assess reproducibility and potential sources of bias are also not reported in the registry record. These include the randomization procedure, allocation concealment, the party or parties masked, and the detailed statistical analysis plan. The registry lists two outcome measures and four analyses, but does not explain the specific models or contrasts, or whether multiplicity was addressed. It also does not report numerical results for the secondary short-chain fatty acid outcome.
The safety information is limited to counts. The types and details of the other adverse events are not reported, and no formal between-group safety analysis is described. As a result, the record supports only a descriptive reading of the listed events, not a detailed safety assessment or causal conclusion.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Effect of Spice Consumption on the Microbiome — NCT03676803.
- Registry record last updated 2019-11-19; status last verified 2019-11.
- Results first posted 2019-11-19.
- 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
The registry record describes a completed randomized, single-masked, parallel pilot study of mixed-spice consumption in healthy participants. Enrollment was 31. The intervention was a daily capsule containing 5 g of mixed spices at culinary dose; the comparator was a placebo capsule containing 5 g of maltodextrin. The primary outcome was change in microbial phylum abundance as a percentage of total bacteria after 2 weeks. Change from baseline in short-chain fatty acids at 2 weeks was listed as a secondary outcome.
Data from one participant in each group were excluded for protocol non-compliance. The registry does not report one reduced primary-outcome comparison or its numerical estimate. It lists zero serious adverse events and zero deaths in both groups, with other adverse events recorded for 2 participants in the mixed-spices group and none in the placebo group. The statistical analysis plan, analysis populations, and protocol-specific sample-size justification are not reported in the registry record.