Taste Perception Pre and Post Bariatric Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Taste Perception Pre and Post Bariatric Surgery (NCT01536197), a registered phase not stated study. The primary outcome is Changes on Taste Detection Thresholds After Bariatric Surgery-induced Weight Loss (Roux-en-Y Gastric Bypass and Laparoscopic Adjustable Banding)..

2. Clinical Question

The outcome is a sensory threshold: the lowest concentration of a tastant that can be detected, expressed in mmol/L. The registry describes measuring that threshold before surgery and at 20% weight loss after surgery. It says the investigators expected that milestone to occur around 3 months post-surgery on average; that is a stated expectation, not a report of when participants were actually assessed.

The record also lists changes in emotional, external, and restricted eating behavior and food craving after weight loss as a secondary outcome, with the description naming Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding. Numerical findings for the primary and secondary outcomes are not reported in the registry record. Consequently, the clinical question can be described, but the direction and size of any observed change cannot be characterized from this record.

3. Trial Design

This is a completed study of taste perception around bariatric surgery. The registry describes pre-surgery testing and follow-up testing at 20% weight loss post surgery. The surgeries themselves were not part of the clinical trial: participants were undergoing the procedures as part of their care, and the record notes that insurance coverage and payment for surgery were separate from the investigators’ testing.

The listed procedures are gastric bypass, gastric banding, and sleeve gastrectomy. The arm descriptions identify people with morbid obesity undergoing each procedure. The primary outcome title, however, specifies Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding, and the secondary outcome description names those procedures as well. The registry record does not explain the difference between those outcome descriptions and the broader set of listed procedures.

The study is not a randomized comparison, and allocation is not stated. The design described is therefore not a randomized head-to-head comparison of the surgical procedures. The pre-surgery measurement serves as a within-participant reference for the later measurement, but that arrangement does not by itself separate changes associated with surgery from changes over time or other influences. No separate control group is described.

The registry lists enrollment of 33 and identifies Washington University School of Medicine as the sponsor. The study start is recorded as 2009-09, primary completion as 2013-05, and status as completed. Those administrative details do not establish how many participants contributed paired measurements or were included in a particular analysis. Those analysis-population details are not reported in the registry record.

4. Participant Flow and Accounting

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

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 Changes on Taste Detection Thresholds After Bariatric Surgery-induced Weight Loss (Roux-en-Y Gastric Bypass and Laparoscopic Adjustable Banding)., measured over we will measure the above outcomes before surgery and at 20% weight loss post surgery, which on average we expect will occur around 3 months post-surgery.

The primary endpoint is change in taste detection thresholds after bariatric surgery-induced weight loss. A taste detection threshold is defined in the registry as the lowest concentration of a tastant that can be detected, measured in mmol/L. The record specifies median as the summary measure and inter-quartile range as the measure of dispersion.

In general, a threshold translates a sensory response into a concentration: it identifies the low end at which a participant can detect a tastant under the test conditions. Repeating the assessment before surgery and at the stated post-surgery weight-loss milestone makes it possible to describe within-participant change. The median gives a measure of the center of the observed threshold distribution that is less affected by extreme observations than the arithmetic mean can be. The inter-quartile range describes the spread of the middle portion of that distribution.

The planned assessment time is defined by reaching 20% weight loss post surgery. The record says this was expected to occur around 3 months post-surgery on average, but it does not report actual assessment timing or outcome values. Although the endpoint is named and its scale and summaries are specified, numerical results are not reported in the registry record. The size, direction, and precision of any change therefore cannot be assessed from the registry information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a repeated measurement of taste detection thresholds: an assessment before surgery and an assessment at 20% weight loss post surgery. In general, repeated measurements allow each participant’s later value to be interpreted relative to that participant’s earlier value. This can reduce the influence of stable differences between participants when describing change, but it does not control for factors that change over time. The registry record does not report the statistical test or model used to analyze these measurements.

What does the median describe?

The primary outcome is summarized by the median. In general, the median is the central value when observations are ordered. It is often useful for measurements whose distributions are skewed or contain unusually high or low observations, because it is less sensitive to those extremes than the mean. The inter-quartile range describes the span of the middle half of the ordered observations and gives information about variability. These summaries describe the distribution; they do not by themselves estimate the within-participant change or provide a test of whether that change is distinguishable from sampling variation.

For a before-and-after question, the distinction between summarizing values at each assessment and summarizing paired changes is important. Separate medians at each assessment do not, by themselves, reveal the median of individual changes. A paired analysis uses the relationship between each participant’s measurements. The registry record does not report whether the analysis was based on individual paired changes, comparisons of distributions at each time, or another method. It also does not report a numerical estimate for the primary outcome.

How should the assessment time be understood?

The endpoint is anchored to reaching 20% weight loss, rather than solely to a fixed calendar visit. The record says that this milestone was expected to occur around 3 months post-surgery on average. In general, an event- or milestone-based assessment can mean that actual follow-up times vary between participants. That variation may matter if the outcome changes with time since surgery. The actual timing distribution and any approach to accounting for it are not reported in the registry record.

What does a confidence interval add?

In general, a confidence interval expresses the statistical uncertainty around an estimated effect under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, but interpretation also depends on the clinical meaning of the endpoint and the design. No confidence interval for the primary outcome is reported in the registry record. There is therefore no registry-based estimate of the precision of any pre- to post-surgery change.

What do the planning illustrations mean?

The sample-size material is described as a planning illustration computed from the observed effect, rather than as the trial’s own design justification. Its stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. The illustrations are planning quantities, not observed power. The numerical effect estimate and the corresponding planning values are not reported in the registry record, so their scale and implications cannot be assessed from the registry information.

In general, planning calculations are conditional on assumptions about the effect to detect, variability, allocation, and analysis. They do not show the probability that a completed study has established an effect, and they cannot replace a reported estimate with its uncertainty. The registry record does not report a sample-size justification for the trial’s original design, or explain whether the planning assumptions reflect that design. The surgeries were not assigned as a randomized comparison, so the stated equal-allocation assumption for an illustration should not be read as evidence that the actual study groups were equally allocated.

Why can group differences be difficult to interpret?

In general, participants receiving different procedures may differ in ways that also relate to the outcome. Random allocation can help balance such factors, while an observational comparison requires design or analysis methods to address them. This study is not described as a randomized comparison, and allocation is not stated. The registry record does not report adjusted estimates or the methods used to address differences between procedure groups. Accordingly, the record does not support interpreting any potential between-group contrast as an isolated effect of procedure.

The general statistical distinctions above explain what the chosen summaries and possible planning calculations can mean. They are not descriptions of an unreported analysis. The registry record identifies the median and inter-quartile range for the primary endpoint, but does not give the analysis method, estimates, or uncertainty measures needed to assess the outcome quantitatively.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists two outcome measures and one analysis. The primary outcome concerns changes in taste detection thresholds. The secondary outcome concerns changes in emotional, external, and restricted eating behavior and food craving after bariatric surgery-induced weight loss; its description names Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding. The record does not report a multiplicity adjustment or explain how the outcomes were prioritized in the analysis beyond identifying the primary and secondary outcomes.

In general, evaluating multiple outcomes can increase the chance that at least one result appears noteworthy by chance if each is tested separately. A prespecified hierarchy or statistical adjustment can address that issue, but the registry record does not describe such a procedure. It also does not report the analysis plan in enough detail to determine which outcomes, contrasts, or time points were included in the reported analysis.

Information about missing measurements and analysis populations is not reported in the registry record. The record does not state how many participants completed both assessments, whether any measurements were excluded, how missing outcome data were handled, or whether analyses included all enrolled participants or a subset. It also does not describe imputation, sensitivity analyses, or reasons for unavailable data. These omissions matter because a before-and-after endpoint depends on having measurements at both assessments, and the participants with complete measurements may differ from those without them.

The enrollment figure alone cannot establish the analysis denominator for the primary endpoint or any secondary outcome. Without denominators, missing-data methods, and outcome estimates, the extent to which missing observations could influence the findings cannot be assessed.

11. 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 lists serious adverse event figures for the gastric bypass and gastric banding groups. For gastric bypass, 23 were listed as at risk, with 0 affected by serious adverse events; the other adverse event figures also list 23 at risk and 0 affected. For gastric banding, 10 were listed as at risk, with 0 affected by serious adverse events; the other adverse event figures list 10 at risk and 0 affected.

These entries describe what was recorded for those groups. They do not establish that no events occurred outside the registry’s reporting scope, and they should not be generalized to the sleeve gastrectomy group, for which no corresponding group appears in the adverse-event figures. Death figures are not reported in the registry record. The registry also does not provide serious adverse event terms or further detail about ascertainment, follow-up, or event definitions. These counts are safety-reporting entries, not a comparison of risks between procedures.

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

The record documents a study question about taste perception before and after bariatric surgery-induced weight loss. It defines a primary measurement as the lowest tastant concentration detectable, gives the unit as mmol/L, and specifies the median and inter-quartile range as summaries. It also identifies a planned post-surgery assessment at 20% weight loss. These details clarify what the investigators intended to measure.

They do not establish what happened to taste detection thresholds. Numerical primary outcome results are not reported in the registry record. There is no reported pre-surgery value, post-surgery value, change estimate, confidence interval, or hypothesis-test result on which to base a statement about direction, magnitude, or precision. The expectation that the weight-loss milestone would occur around 3 months post-surgery on average is not an observed result.

The before-and-after structure can describe measurements over time, but it does not by itself establish that surgery caused any change. The record does not describe a randomized comparison or a like-for-like control group. It also does not explain the relationship between the primary outcome’s named procedures and the broader set of listed surgical groups. Those design and reporting limits should remain part of any reading of the study.

The serious adverse event entries report zero affected participants in the listed gastric bypass and gastric banding groups, with their respective at-risk counts. They do not provide a complete safety account for all listed procedures, and death figures are not reported in the registry record. In short, the record shows what question was posed and how a key endpoint was defined, but does not provide the outcome findings needed to judge the observed change or its uncertainty.

13. Why This Trial Matters Statistically

This study illustrates why a clearly defined endpoint and an interpretable comparison are both important. Taste detection thresholds turn a sensory response into a measurable concentration, and the record states the unit and the summary measures. Repeating the measurement before surgery and at a weight-loss milestone creates a framework for describing change over time.

Statistically, however, a defined endpoint is not the same as a reported result. Without numerical measurements or an estimate of change, readers cannot assess the direction, size, or precision of the findings. This distinction is central when interpreting registry entries: registration details may describe the question and measurement plan without supplying the evidence needed to evaluate the outcome.

The study also highlights the limits of a nonrandomized, pre-post design. Repeated measurements can account for stable individual differences in a descriptive comparison, but they cannot on their own rule out changes over time or other explanations. Nor does a comparison between procedure groups automatically isolate differences attributable to the procedures. The record does not report a randomized allocation, a control group, or adjustment methods.

Finally, alignment between the stated endpoint and the listed study groups matters. The primary outcome description names Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding, while the study arms also include sleeve gastrectomy. The registry does not clarify that scope. Together with the absence of numerical outcome results, this limits what can be learned from the record about the clinical question, even though the endpoint and broad measurement timing are specified.

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 leaves important details about measurement and analysis unresolved. It defines taste detection threshold and gives the planned unit and summary measures, but it does not report the tastants assessed, the testing procedure, or how threshold observations were combined across tastants. The endpoint description refers to a threshold measure, but the record does not explain whether the principal analysis concerns each tastant separately or an aggregate.

The timing is tied to 20% weight loss, with an expectation that this would occur around 3 months post-surgery on average. Actual follow-up timing, the range of time to reach the milestone, and the number assessed at that point are not reported in the registry record. The description of the primary outcome names Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding, while the listed groups also include sleeve gastrectomy; how the sleeve group was treated for the primary endpoint is not explained.

The record does not report numerical outcome findings, analysis methods, confidence intervals, or the handling of missing assessments. It also does not describe how potential differences among participants undergoing the procedures were addressed. The absence of a randomized comparison and the lack of a stated allocation method limit interpretation of between-procedure contrasts. Because surgery was not part of the trial, the registry’s description also does not make the trial a controlled evaluation of the surgical procedures themselves.

Finally, the adverse-event groups listed do not include a corresponding sleeve gastrectomy entry, and death figures are not reported in the registry record. These reporting gaps limit interpretation of both the outcome and safety information available in the record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Taste Perception Pre and Post Bariatric Surgery — NCT01536197.
• Registry record last updated 2017-12-18; status last verified 2017-11.
• Results first posted 2014-07-03.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry identifies a completed study titled “Taste Perception Pre and Post Bariatric Surgery,” sponsored by Washington University School of Medicine. It lists enrollment of 33, a start date of 2009-09, and primary completion at 2013-05. The listed procedures are gastric bypass, gastric banding, and sleeve gastrectomy; the surgeries were not part of the clinical trial.

The primary outcome is change in taste detection thresholds, measured in mmol/L and summarized by median and inter-quartile range. The planned assessments were before surgery and at 20% weight loss post surgery, expected around 3 months post-surgery on average. The registry record does not report numerical primary outcome results, analysis methods, or confidence intervals. It lists two outcome measures and one analysis. Serious adverse event entries are reported for gastric bypass and gastric banding, while death figures are not reported in the registry record.