Daily Caloric Restriction and Intermittent Fasting in Overweight and Obese Adults With Autosomal Dominant Polycystic Kidney Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Daily Caloric Restriction and Intermittent Fasting in Overweight and Obese Adults With Autosomal Dominant Polycystic Kidney Disease (NCT03342742), a randomized na study. The primary outcome is Feasibility to Retain Participants.

2. Clinical Question

3. Trial Design

This was a randomized, double-masked, parallel-group behavioral intervention study sponsored by the University of Colorado, Denver. The registry lists enrollment as 29. The study began on 2018-06-04, reached primary completion on 2020-10-13, and has a completed status. Its population was overweight or obese adults with autosomal dominant polycystic kidney disease.

The two groups were assigned different patterns of energy restriction. Daily caloric restriction used a stated daily energy deficit of 34% relative to baseline individual weight-maintenance requirements. Intermittent fasting involved a single meal at about 20% of estimated energy requirements on three non-consecutive days each week, with a stated weekly energy deficit of about 34%. Thus, the intended weekly deficit was described as similar, while its timing differed.

The study was described as a pilot assessing the feasibility of delivering the behavioral interventions over one year, as well as safety, acceptability, and tolerability. It was also intended to provide initial insight into biological changes and kidney growth. The primary endpoint is a participant count, while posted secondary results include serum insulin-like growth factor-1 (IGF-1) measurements at baseline, 12 weeks, and 1 year. The registry record does not report the masking procedures, the method used to generate or conceal random assignments, or a detailed schedule of study visits beyond the outcome timeframes.

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: One participant dropped out prior to randomization. This individual is included in the protocol enrollment number, but not the number of participants started.

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 Feasibility to Retain Participants, measured over Through study completion, an expected duration of 18 months.

The primary endpoint is titled “Feasibility to Retain Participants” and uses a count of participants. Its description refers to the numbers of individuals enrolled, with assessment through study completion and an expected duration of 18 months. A participant count can describe the scale of enrollment and is a straightforward feasibility measure, but it is not the same as a retention proportion: a proportion would require a clearly specified starting group and a defined count of participants retained at a particular follow-up point.

The registry reports a count of 15 for daily caloric restriction and 13 for intermittent fasting. It does not explain how these counts operationalize retention, identify a retention threshold, or give a count explicitly labeled as completing follow-up. Consequently, the endpoint should be read as the posted participant-count outcome rather than as evidence about a retention rate. The registry record does not report a prespecified feasibility target or an explanation of how the count would determine whether delivery was feasible.

Using a count is appropriate for describing how many participants are recorded for an outcome. It does not, by itself, establish whether participants found an intervention acceptable, tolerated it, or completed the intended intervention. Those are related but distinct feasibility dimensions, and the record describes them as study aims without giving a detailed decision rule for the primary endpoint.

7. Results Posted in the Registry

• Intermittent Fasting: 100.0% (13/13) versus 100.0% (15/15) on control; risk difference 0.0 percentage points (95% CI 0.0 to 0.0), risk ratio 1.00 (1.00–1.00); unadjusted two-proportion z-test p = n/a.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Serum Insulin-like Growth Factor-1 Levels at Baseline

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Intermittent Fasting: mean 93.00 versus 104.00 on control; difference -11.00 (95% CI -33.12 to 11.12), standardized effect d = -0.37; z-test p = 0.330.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Intermittent Fasting and the control. The interval gives the range of effects that remain compatible with the data.

Serum Insulin-like Growth Factor-1 Levels at 12 Weeks

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Intermittent Fasting: mean 96.00 versus 127.00 on control; difference -31.00 (95% CI -61.74 to -0.26), standardized effect d = -0.84; z-test p = 0.048.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Intermittent Fasting than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Serum Insulin-like Growth Factor-1 Levels at 1 Year

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Intermittent Fasting: mean 101.00 versus 103.00 on control; difference -2.00 (95% CI -25.73 to 21.73), standardized effect d = -0.07; z-test p = 0.869.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Intermittent Fasting and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes span several domains, including safety and tolerability, quality of life, mood, energy intake, and biological measures. The posted numerical secondary results include IGF-1 means at baseline, 12 weeks, and 1 year. The registry record does not report numerical results for the other listed secondary outcomes or a set of reported analyses for the IGF-1 comparisons. Thus, the available secondary evidence provides only a partial view of the broader outcomes the study intended to examine.

Across the three IGF-1 timepoints, the group means and estimated differences do not follow a single consistent pattern: the baseline and 1-year comparisons are close to zero relative to their intervals, while the 12-week comparison is more separated and its interval lies below zero. These are separate comparisons at particular timepoints. They do not establish that one group changed more from baseline, because a change score or longitudinal comparison is not reported. Nor do they explain why the group means vary across timepoints.

The primary participant-count outcome addresses feasibility differently from the biological secondary outcomes. A count of participants does not establish whether IGF-1 changed, and the IGF-1 comparisons do not clarify whether participants were retained or whether the intervention was acceptable. The outcomes answer distinct questions and should not be treated as interchangeable evidence.

General statistical context: when multiple outcomes and timepoints are examined, some unadjusted results may appear noteworthy by chance alone. An unadjusted p-value does not account for that multiplicity. The registry record does not report a multiplicity adjustment or identify a hierarchy of confirmatory and exploratory outcomes. The secondary findings therefore carry less confirmatory weight than results from a prespecified analysis with a reported multiplicity strategy. In a pilot study, descriptive patterns can still help formulate questions for later research, but they should not be treated as definitive evidence.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Safety and Tolerability, Measured as Adverse Events
• Quality of Life Scores at Baseline
• Quality of Life Scores at 12 Weeks
• Quality of Life Scores at 1 Year
• Mood at Baseline
• Mood at 12 Weeks
• Mood at 1 Year
• Change in Energy Intake

9. Statistical Interpretation

10. Statistical Methods Explained

The registry identifies the study as randomized, double-masked, and parallel-group. In general, randomization aims to make assigned groups comparable on average, while masking is intended to limit the influence of knowledge about assignments on study conduct or assessment. These design labels do not establish how assignment was generated, who was masked, or whether masking was maintained; those details are not reported in the registry record.

How to read the primary comparison

The primary outcome is a participant count. The registry reports counts of 15 for daily caloric restriction and 13 for intermittent fasting, alongside a risk difference of 0.0, limits of 0.0 and 0.0, and p = 1.0. A risk difference usually expresses the difference between two proportions of participants experiencing an outcome. In this record, the endpoint is described as a count of individuals enrolled, and the record does not clarify the construction behind the risk-difference statistic. It is therefore important not to reinterpret the reported count comparison as a retention proportion or as a measure of treatment efficacy.

In general, a p-value describes how compatible data are with a specified null model, under the assumptions of the analysis. It is not the probability that the null hypothesis is true, nor does it measure the size or practical importance of a difference. The registry record does not report a detailed statistical analysis plan for the primary endpoint, so the calculation and its assumptions cannot be assessed beyond the posted statistics.

How to read the continuous-outcome comparisons

The secondary IGF-1 outcomes are reported as group means with standard deviations. A mean describes the average observed value in a group; a standard deviation describes the spread of observations around that group mean. The comparison is expressed as the intermittent-fasting mean minus the daily-caloric-restriction mean. Negative estimates therefore indicate a lower reported mean in the intermittent-fasting group at that timepoint, not necessarily a difference in change from baseline.

For example, the posted mean differences are -11 ng/ml at baseline, -31 ng/ml at 12 weeks, and -2 ng/ml at 1 year. These estimates are unadjusted comparisons of the group means at each timepoint. They do not account for the baseline value in a longitudinal model, and the registry record does not report an adjusted model, a repeated-measures analysis, or an analysis of within-participant change. The confidence intervals describe uncertainty in the estimated mean differences under the calculation used; they do not account for unreported sources of bias or model misspecification.

General statistical context: a confidence interval gives a range of values compatible with the observed data and the assumptions of the procedure. Wider intervals indicate less precision. An interval that includes zero does not establish that there is no difference; it indicates that the data and method do not distinguish zero from the values covered by the interval at the stated confidence level. The confidence level is not specified in the registry record, so no particular level should be attributed to these intervals.

What the planning illustrations mean

The registry’s planning illustrations use the observed effect as a starting point and show participant counts per arm for specified fractions of that effect. The stated assumptions are a two-sided significance level of 0.05, equal allocation, and a normal approximation. For the 12-week IGF-1 comparison, for example, the illustration for 100% of the observed effect gives 23 participants per arm for 80% power and 30 participants per arm for 90% power. The corresponding illustrations for 75% of the observed effect are 40 and 53 participants per arm; for 50% of the observed effect they are 89 and 119 participants per arm.

These values are planning illustrations, not observed power and not evidence that the trial was designed to achieve those targets. They are sensitive to the observed effect, which can be unstable in a small pilot. The record does not report that these calculations were used in the trial’s original design, or give a sample-size justification, target effect, or formal power calculation for the trial. General statistical context: a smaller target effect generally requires more observations to distinguish it from random variation, if other assumptions remain fixed.

The registry also does not report the statistical methods used to handle missing observations, multiplicity across outcomes, or the analysis population for each outcome. These omissions limit the extent to which the posted comparisons can be evaluated as confirmatory analyses. They do not invalidate the descriptive summaries, but they require cautious interpretation of inferential results.

11. Confidence Intervals and Precision

The uncertainty around the secondary mean differences varies by timepoint. At baseline, the estimated difference in IGF-1 was -11 ng/ml, with a confidence interval from -33.12 to 11.12. At 12 weeks, the estimate was -31 ng/ml, with a confidence interval from -61.74 to -0.265. At 1 year, the estimate was -2 ng/ml, with a confidence interval from -25.73 to 21.73. The 12-week interval lies below zero, whereas the baseline and 1-year intervals include zero. These intervals are unadjusted, and the registry record does not specify their confidence level.

In general, a confidence interval communicates both the direction and precision of an estimate. A broad interval allows a wider range of underlying differences than a narrow interval. An interval that includes zero is compatible with no difference under the calculation, but it can also be compatible with differences in either direction. It should not be interpreted as proof that the groups are identical. Conversely, an interval excluding zero does not by itself show that the difference is important or that the result is robust to multiple testing, missing data, or other analytic choices.

The available intervals should be considered in the context of the reported group sizes at each timepoint: 15 and 13 at baseline, 11 and 11 at 12 weeks, and 10 and 10 at 1 year. These summaries do not establish why the numbers contributing to each outcome differ across timepoints. The registry record does not report an analysis of missingness or a method for accounting for incomplete follow-up. Precision is therefore only one part of the uncertainty; possible selection effects and the exploratory nature of a pilot also matter.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple outcome domains and several IGF-1 assessment times, creating the possibility of multiple statistical comparisons. The available IGF-1 p-values are labeled unadjusted. The registry record does not report whether a multiplicity strategy was prespecified, whether outcomes were ranked by priority, or whether any adjustment was applied. Without that information, the 12-week unadjusted result should be interpreted as exploratory rather than as a result that has been protected against the chance of false-positive findings across multiple comparisons.

The record also does not report how missing data were handled, whether an analysis included all randomized participants, or whether analyses were restricted to participants with available measurements. Group sizes for the IGF-1 summaries vary by timepoint, but the reason for those differences and the characteristics of participants without measurements are not reported in the registry record. It is therefore not possible to determine from these summaries whether missingness could have affected the comparisons.

For the primary endpoint, the registry gives participant counts and a comparison, but does not report a detailed analysis population or explain how the endpoint’s “retain participants” title relates to its description as numbers enrolled. No retention threshold, prespecified feasibility criterion, or missing-data method is reported. These are important distinctions: enrollment, continued participation, and completion are not identical concepts.

The registry record does not report a statistical analysis plan, a sample-size justification, interim analyses, or whether analyses were adjusted for baseline characteristics. It also does not report the exact population used for each analysis. These omissions do not change the descriptive numbers, but they limit reproducibility and make it difficult to judge whether the inferential comparisons followed prespecified methods.

13. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent non-serious adverse event terms

The serious adverse event summaries report zero serious adverse events in each group and zero deaths in each group. For other adverse events, the registry reports 10 in the daily caloric restriction group and 13 in the intermittent fasting group. These are the counts recorded in the registry; they should not be read as proof that serious risks are absent or that the groups have equivalent safety profiles.

In general, adverse-event counts require context about how events were defined, collected, attributed, and followed. The registry record does not report detailed event terms for serious events, and no top serious-event terms are listed. It also does not provide enough information to determine from these counts whether “other” adverse events refer to events, participants experiencing events, or a particular severity category. The record describes safety and tolerability as study aims, but the counts alone do not establish a comparative safety conclusion. The small pilot and the lack of detailed event descriptions limit the strength of any safety interpretation.

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

The posted results describe a pilot randomized comparison of two behavioral patterns of energy restriction in overweight or obese adults with ADPKD. The primary outcome is a participant count, reported as 15 for daily caloric restriction and 13 for intermittent fasting. Its title refers to retaining participants, while its description refers to numbers enrolled. Because the registry does not report a retention rate or clarify this difference in wording, the result should be understood as a reported count rather than a complete measure of retention.

The IGF-1 results are descriptive group means and unadjusted comparisons at baseline, 12 weeks, and 1 year. They are not a reported analysis of change over time, kidney growth, or the overall biological response to either intervention. The study’s stated aims included initial insight into biological changes and kidney growth, but the registry record does not report a numerical kidney-growth result in the material available for interpretation.

These results do not establish that either intervention is superior, equivalent, or effective for a clinical purpose. The p-values and confidence intervals address particular statistical comparisons, not the full set of questions about feasibility, acceptability, tolerability, kidney outcomes, or clinical benefit. In particular, a non-significant comparison is not proof that two approaches are the same, and a nominally small unadjusted p-value is not, by itself, confirmatory evidence.

General statistical context: pilot studies can describe recruitment, delivery, and early outcome patterns, and can inform the design of later research. Estimates from a pilot may be imprecise and can vary substantially with the participants observed. The registry record does not report whether the study met a prespecified feasibility criterion or how the results were intended to guide subsequent work. Readers should therefore treat the posted findings as limited descriptive and exploratory evidence, not as a basis for individual treatment decisions.

15. Why This Trial Matters Statistically

This trial is statistically instructive because its primary outcome highlights the importance of matching an endpoint’s title, definition, and analysis. “Feasibility to Retain Participants” suggests follow-up or completion, while the endpoint description refers to numbers enrolled. A count can be useful, but its interpretation depends on what was counted, at what point, and relative to which starting population. Without a clear operational definition, a numerical comparison can be reported accurately yet remain difficult to connect to the intended feasibility question.

The registry also illustrates the difference between a pilot’s descriptive results and confirmatory evidence. Group means and confidence intervals give useful information about the observed IGF-1 data, but the small timepoint-specific groups and unadjusted comparisons leave substantial uncertainty. One comparison has an interval that excludes zero, but the registry does not report a multiplicity strategy or longitudinal analysis. That makes it especially important to distinguish a signal for further study from a firm conclusion.

Planning illustrations provide another lesson. Their participant counts are explicitly based on observed effects and stated assumptions, rather than a reported original design calculation. Such illustrations can show how planning depends on the effect one aims to detect, but they are not observed power and should not be mistaken for the trial’s planned sample size.

Finally, feasibility, biological outcomes, and safety are separate questions. Participant counts do not answer whether an intervention is acceptable or changes a biological measure, and a short list of adverse-event counts cannot fully characterize safety. Clear endpoint definitions, prespecified analysis methods, and transparent accounting for missing data and multiple comparisons would help later studies make these distinctions more assessable.

16. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several limitations specific to this record affect interpretation. The primary endpoint title refers to retaining participants, but its description specifies numbers enrolled. The record reports counts by group without a retention proportion, completion count, or operational definition that reconciles the title and description. It also does not give a prespecified threshold for judging feasibility. As a result, the primary count is difficult to interpret as a direct measure of retention.

The registry describes the study as a pilot and reports a relatively small set of participants contributing to the outcome summaries. The IGF-1 comparisons are presented separately by timepoint, with no reported longitudinal analysis or comparison of changes from baseline. The record does not report why group sizes differ across timepoints, how missing observations were handled, or whether the analyzed participants were selected according to a prespecified analysis population.

Although the registry lists safety, quality of life, mood, energy intake, biological change, and kidney growth among the study’s aims or outcomes, numerical results for these domains are not all reported in the record. The available adverse-event counts lack detailed serious-event terms, and the registry does not provide a full account of event definitions or attribution. This limits assessment of safety and tolerability.

The record does not report the statistical analysis plan, the sample-size justification, an interim-analysis plan, or a multiplicity procedure. The unadjusted secondary comparisons and effect-based planning illustrations should therefore be read as exploratory or illustrative. These limitations are about what can be established from the registry record; they do not show that unreported procedures were or were not conducted.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Daily Caloric Restriction and Intermittent Fasting in Overweight and Obese Adults With Autosomal Dominant Polycystic Kidney Disease — NCT03342742.
• Registry record last updated 2022-03-03; status last verified 2022-02.
• Results first posted 2022-03-03.
• 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.

20. Record Summary

The completed study was a randomized, double-masked, parallel-group behavioral pilot in overweight or obese adults with autosomal dominant polycystic kidney disease. It compared daily caloric restriction with intermittent fasting, with a stated weekly energy deficit of about 34% for each approach. The registry lists enrollment as 29 and records the study start as 2018-06-04 and primary completion as 2020-10-13.

The primary outcome is a participant count, reported as 15 for daily caloric restriction and 13 for intermittent fasting. The record’s wording does not clearly distinguish enrollment from retention. Secondary results include mean IGF-1 levels at baseline, 12 weeks, and 1 year, with unadjusted group comparisons. The registry does not report a detailed analysis plan, missing-data methods, or multiplicity adjustment. The findings are best read as descriptive and exploratory pilot results.