The Effect of Glucomannan Soluble Fiber on Glucose Homeostasis in Patients With Roux En Y (RNY) Gastric Bypass Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of Glucomannan Soluble Fiber on Glucose Homeostasis in Patients With Roux En Y (RNY) Gastric Bypass Surgery (NCT02336438), a non-randomized phase 4 study. The primary outcome is Difference Score: Percent of Time Spent in Hypoglycemic State.

2. Clinical Question

The question reflects the registry’s proposed rationale: soluble fiber might alter glucose absorption and the movement of food through the digestive tract, with a possible effect on post-meal glucose patterns. These are proposed mechanisms, not findings from this study. The registry identifies postprandial hypoglycemia as the clinical context and describes the project as a pilot. It does not report a treatment effect, a confidence interval, or a statistical test for the primary outcome. Consequently, the direction and precision of the observed comparison cannot be assessed from the registry record.

3. Trial Design

The registry identifies this as a completed Phase 4 study sponsored by Bassett Healthcare. It records a non-randomized allocation, no masking, a crossover model, and an enrollment of 10. The recorded start was 2013-05, primary completion was 2014-11, and study status is completed. These design labels describe the registry entry; they do not supply details about how participants entered each phase or how observations were analyzed.

The listed phases are Baseline Phase (Control) and Treatment Phase (Glucomannan). Each phase description refers to wearing an iPro continuous glucose monitoring device for 5 days, keeping a diet history, and checking blood glucose at home four times a day using a One Touch glucometer. Both descriptions also mention a mixed meal tolerance test, but the text ends before giving its details. The number and timing of tests, their relation to monitoring, and the procedures used to establish phase order are not reported in the registry record.

A crossover design can compare measurements from the same participants under different conditions. Such comparisons can account for stable differences between participants, but they also depend on how treatment order, time effects, and possible carryover are handled. Here, allocation is explicitly recorded as non-randomized. The sequence, any washout interval, and any adjustments for period or order are not reported in the registry record. The registry itself cautions that the arms are not a like-for-like control comparison because the allocation was not randomized. The primary endpoint is a treatment-minus-control difference score, but the analytic method used to estimate it is not described.

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

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 Difference Score: Percent of Time Spent in Hypoglycemic State, measured over 10 days.

The primary endpoint is the difference in the percent of time spent in a hypoglycemic blood glucose range, defined in the registry as blood glucose below 70. It is a continuous measure derived from continuous glucose monitoring. For each comparison, the registry defines the difference score as the percent of monitored time below that threshold during the glucomannan phase minus the corresponding percent during the control phase. The stated timeframe is 10 days.

This endpoint captures how much monitored time falls in a specified glucose range rather than counting only isolated readings or events. Continuous monitoring can describe patterns across the monitoring period, while a percentage expresses the share of monitored time in the range of interest. The endpoint therefore reflects duration as recorded by the device; it is not, by itself, a measure of symptoms, severity of individual episodes, or broader clinical outcomes.

The registry’s rationale is that post-meal glucose patterns are relevant to the hypoglycemia described in this population and that soluble fiber was proposed as a way to modify glucose absorption. That rationale does not establish that the endpoint changed. The record does not report the treatment-minus-control estimate, its standard deviation, a confidence interval, a p-value, or the number of participants contributing to the primary analysis. Without those results, the magnitude, direction, and precision of the observed difference cannot be assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary measure as the mean of a continuous difference score, with standard deviation as its dispersion measure. A continuous variable can take values across a range rather than being limited to categories. Here, each phase is represented by a percentage of monitored time in the specified glucose range, and the endpoint is the subtraction of one phase’s percentage from the other. The mean summarizes the average difference across analyzed observations; the standard deviation describes how spread out those differences are. Neither statistic is reported in the registry record.

What does the treatment-minus-control score mean?

The sign of a difference depends on the order of subtraction. In this record, the treatment value is minus the control value. Thus, a score below zero would correspond to a smaller percentage of time in the specified range during the glucomannan phase, and a score above zero would correspond to a larger percentage. A score of zero would represent no difference in the two phase percentages for the comparison being summarized. These are general interpretations of the defined score, not descriptions of the study’s unreported result.

A difference score can make the comparison direct and preserve the pairing of phase measurements within a participant. In a crossover setting, the same participant may contribute observations under both conditions, so the two measurements are generally not independent. A paired analysis uses that relationship when estimating the average difference and its uncertainty. The registry does not say whether the reported analysis used a paired method or describe any model used for the primary outcome. The method therefore cannot be evaluated from the record.

Why does the crossover structure matter?

General statistical consideration: a crossover design may reduce the influence of stable participant characteristics because each participant can serve as their own comparison. However, the estimate may also be affected by changes over time, sequence effects, or carryover from one phase into another. Randomized phase order can help address some sources of bias, but the study is recorded as non-randomized. Its phase sequence, washout procedures, and methods for handling time or order are not reported in the registry record. The crossover label alone does not establish that these issues were addressed.

The registry describes continuous glucose monitoring in both phases and home glucose checks four times a day. General measurement consideration: repeated device readings within a participant are correlated, rather than equivalent to a set of independent participants. An analysis must define how readings are converted into participant-level percentages and how participant-level differences contribute to the summary. The registry defines the percentage and difference score but does not provide this analytic detail, nor does it report the amount of usable monitoring for each participant.

How should uncertainty be understood?

General statistical explanation: a confidence interval gives a range of effect estimates compatible with the data and the method used, reflecting sampling uncertainty. A narrow interval indicates greater precision than a wide one, though precision is not the same as freedom from bias. A p-value, when reported, summarizes how unusual data at least as discrepant as those observed would be under a specified null model and its assumptions. It does not measure the probability that a treatment works, and it does not show whether an effect is important in practice. The registry record does not report a confidence interval or p-value for the primary outcome, so neither precision nor statistical evidence can be assessed.

The study record lists a standard deviation but does not state whether it refers to individual paired differences or another quantity. That distinction matters because the variability of paired differences is not generally interchangeable with variability in each phase considered separately. The record also does not specify an analysis population, missing-data procedure, adjustment for baseline characteristics, or a model for repeated measurements. These omissions prevent a full reconstruction of the primary analysis from the registry description.

What do the planning assumptions describe?

General planning explanation: a sample-size illustration estimates the number of participants that might be needed under chosen assumptions; it is not an estimate of what the trial actually achieved. The planning description associated with this study uses a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. It describes the illustration as based on the observed effect, not as the study’s own design justification. The record does not report a sample-size justification or planning assumptions used to set enrollment. Any planning values should be understood as hypothetical illustrations, not observed power or evidence about the study’s outcome. The registry’s crossover design also differs from the equal-allocation, two-arm framing described for the planning calculation, so that illustration should not be mistaken for a reconstruction of the trial design.

Over-dispersion is a general concern when observed variability exceeds what a statistical model assumes. If a model understates variability, its uncertainty estimates can be too small and its intervals too narrow. The registry does not report a model for the primary outcome or evidence about over-dispersion; this is a general methodological consideration, not a finding about this study. More broadly, the registry’s outcome definition and design labels are not enough to determine whether the analysis model matched the dependence and variability in the collected data.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Baseline Phase (Control) and Treatment Phase (Gluc")
n   <- c(10)
m   <- c(1.2)
sp  <- c(8.2)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Baseline Phase (Control) and Treatment Phase (Gluc  10  1.200  8.200  -4.666  7.066

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies two secondary outcomes: the difference score for percent of time within normal blood glucose limits and the difference score for percent of time with elevated blood glucose. It also lists 6 outcome measures and 6 analyses. The record does not report how many outcomes were designated primary in the protocol, whether the secondary outcomes were prespecified, or whether any multiplicity adjustment or testing hierarchy was used.

General statistical explanation: when several hypotheses are tested, the chance of at least one apparently unusual result can increase if each is assessed without accounting for the others. A prespecified hierarchy, adjustment, or clear distinction between confirmatory and exploratory analyses can help readers interpret a collection of results. No such strategy is reported in the registry record. The secondary outcome results are also not reported, so their direction and precision cannot be considered alongside the primary outcome.

The record does not describe missing-data handling, participant exclusions, withdrawals, or the analysis population for any outcome. It does not report how much monitoring data were unusable or whether participants had complete measurements in both phases. This matters for a crossover comparison because estimating a within-participant difference ordinarily requires usable information from both conditions. General statistical consideration: if missingness is related to glucose patterns, participant characteristics, or treatment phase, the analyzed group may not represent everyone enrolled. The registry does not provide enough information to assess whether missingness occurred or how it could affect results.

There is no reported protocol-level analysis plan or information about interim analyses in the registry record. Their existence, absence, or details should not be inferred. With no reported outcome estimates, testing procedures, or analysis populations, the registry entry does not support a judgment about statistical significance or robustness.

12. Safety Results

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

Other (non-serious) adverse events

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

The registry’s adverse-event entry lists Baseline Phase (Control) and Treatment Phase (Glucomannan) together. It records 11 participants at risk for serious adverse events and 0 affected, and 11 at risk for other adverse events and 0 affected. No serious adverse event terms are listed. The deaths field is not reported in the registry record.

These figures describe the adverse-event fields as entered; they do not establish that every possible event was actively assessed or that all participants had complete safety follow-up. The number at risk differs from the overall enrollment of 10 recorded for the study. The registry does not explain that difference, so the denominator should not be silently treated as the enrollment figure or reconciled by assumption.

A zero count in a registry entry means that no events are recorded in that field for the listed group. It does not prove that the risk of an event is absent, and it cannot by itself establish comparative safety. The entry combines the two phases rather than presenting separate phase-specific counts, and the record does not describe the event collection window or ascertainment procedures. These details limit what can be inferred from the posted counts.

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

The registry record identifies a small pilot crossover study of glucomannan in the setting of postprandial hypoglycemia after Roux-en-Y gastric bypass. It defines a primary outcome that compares the percentage of monitored time below a blood glucose threshold during treatment and baseline control phases. That definition makes the intended comparison clear, but the numerical primary result is not reported in the registry record.

Without the estimate, standard deviation, confidence interval, or p-value, the posted information does not establish whether the treatment-phase percentage was higher or lower, how large any difference was, or how precisely it was estimated. It also does not allow readers to distinguish a stable pattern from a difference that could reflect sampling variation or study design limitations. The lack of these results is not evidence that there was no effect; it means the effect cannot be evaluated from the registry information described.

The design places additional limits on interpretation. Allocation was non-randomized and masking was absent. The record does not explain phase order, washout, or analytic adjustments for period and sequence. Those details are important when interpreting a within-participant comparison because outcomes may vary over time or depend on what happened in an earlier phase. The registry does not report enough information to assess whether such possibilities affected the comparison.

The registry’s rationale presents fiber as a proposed dietary approach that might alter glucose absorption and related glucose patterns. A proposed mechanism is not a measured treatment effect. The listed endpoint is a glucose-monitoring measure; it does not directly report symptoms, quality of life, disability, or other clinical outcomes. The record also does not report detailed participant characteristics, a complete analysis plan, or outcome data for the listed secondary measures. Accordingly, the entry can describe the study question and recorded design, but it cannot establish the magnitude, precision, or broader clinical importance of a treatment effect.

14. Why This Trial Matters Statistically

This study raises statistical issues that are common in pilot research using continuous monitoring and crossover designs. The endpoint is not a simple count of events: it is the percentage of monitored time in a specified glucose range, compared between phases. Interpreting such a measure depends on how repeated device readings are summarized, how participants contribute to the analysis, and how incomplete monitoring is handled. The registry defines the endpoint but does not provide those analytic details or report its result.

The crossover structure also makes the unit of analysis important. A within-participant comparison can account for stable differences between participants, but its uncertainty depends on the variability of the paired differences. Non-randomized phase allocation and unreported sequencing and washout details leave potential period and carryover questions unresolved. These design features show why a label such as crossover cannot substitute for a description of the analysis.

The entry illustrates the distinction between a trial’s observed results and a planning calculation. Planning illustrations based on an observed effect are hypothetical exercises under stated assumptions; they are not observed power and do not show that the study was adequately sized. The registry does not report a trial-specific sample-size justification. With enrollment recorded as 10 and no primary estimate or uncertainty interval, neither the observed precision nor the strength of evidence can be judged from the registry record.

Finally, the record lists multiple outcomes without describing a multiplicity approach, and it does not report missing-data or analysis-population details. Those omissions matter because interpretation depends not only on the endpoint but also on which participants and measurements contribute and how multiple comparisons are handled. The study is statistically informative as an example of questions that must be answered to interpret a pilot comparison, while the posted registry information remains insufficient to quantify the primary result.

15. 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 primary limitation for interpreting this specific trial is that the registry record does not report the primary outcome estimate or its uncertainty. It gives the endpoint definition and timeframe but not the mean difference, standard deviation, confidence interval, or p-value. The two listed secondary outcome results are also not reported. The size and direction of any observed changes therefore cannot be assessed.

The design description is incomplete for evaluating a crossover comparison. The record identifies non-randomized allocation, no masking, and a crossover model, but does not report phase order, washout procedures, or how period, sequence, and carryover were addressed. It also does not specify the statistical method used for the difference score or confirm whether the analysis accounted for paired observations.

The registry records enrollment of 10, while the adverse-event entry lists 11 participants at risk. The record does not explain the discrepancy. It does not report the number of participants with usable primary outcome data, withdrawals, exclusions, missing monitoring, or the population used for each analysis. Participant characteristics and detailed eligibility criteria are also not reported in the registry record.

The phase descriptions mention continuous glucose monitoring, home glucose checks, a diet history, and a mixed meal tolerance test, but do not give the full procedures or the test details. The registry does not report the glucomannan dose or timing, a trial-specific sample-size justification, an analysis plan, or a multiplicity strategy. These limitations constrain evaluation of the outcome measurement, comparability of phases, precision, and potential sources of bias. They do not establish that a particular problem occurred; they identify information the record does not report.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The Effect of Glucomannan Soluble Fiber on Glucose Homeostasis in Patients With Roux En Y (RNY) Gastric Bypass Surgery — NCT02336438.
• Registry record last updated 2017-03-13; status last verified 2017-01.
• Results first posted 2015-09-21.
• 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.

19. Record Summary

The registry record describes a completed Phase 4, non-randomized, unmasked crossover study sponsored by Bassett Healthcare, with enrollment of 10. The recorded start was 2013-05 and primary completion was 2014-11. The study concerns glucomannan in patients after Roux-en-Y gastric bypass and identifies postprandial hypoglycemia as its clinical context.

The primary endpoint is the treatment-minus-control difference in percent of monitored time with blood glucose below 70, over a stated timeframe of 10 days. The registry also lists secondary outcomes for time within normal and elevated glucose limits. It describes continuous glucose monitoring and home glucose checks during the two phases, but does not report the primary or secondary outcome results, the analysis method, or key details of phase order and missing data.

The adverse-event entry records 0 serious and 0 other adverse events among 11 at risk, while the study enrollment is recorded as 10; the record does not explain the difference. Overall, the registry information establishes the question and broad design but does not permit assessment of the treatment-effect estimate or its precision.