Long-term Caloric Restriction and Cellular Aging Markers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Long-term Caloric Restriction and Cellular Aging Markers (NCT01256840), a registered phase not stated study. The primary outcome is Telomere Length.

2. Clinical Question

This is an observational, cross-sectional question rather than a test of an assigned treatment. Telomere length was assessed from a blood draw on the study day, with no follow-up described. The design can examine whether the groups differ at that assessment, but by itself cannot establish that calorie restriction caused any difference. People in the groups may differ in other ways, and the registry record does not report whether such differences were measured or adjusted for. The record does not report the group-specific telomere-length estimates or the results of statistical comparisons, so it does not establish whether the groups differed.

3. Trial Design

The registry record identifies the study as the Caloric Restriction With Optimal Nutrition and Aging Study, sponsored by the University of California, San Francisco. It lists an enrollment of 71, a start date of 2010-12, a primary completion date of 2014-08, and a status of completed. The study description explicitly states that this is not a clinical trial, although registration was required by the UCSF Committee on Human Research.

The design is described as a one-time assessment involving a blood draw from calorie-restricting participants, normal-eating controls, and an obese comparison group. The outcome timeframe is listed as one day; the description clarifies that telomere length is assessed on the study day and that there is no follow-up. Thus, the record describes a cross-sectional comparison, not a longitudinal assessment of change in telomere length.

No random allocation is described, and the record does not state how participants entered each group. It also cautions that the arms are not a like-for-like control comparison. The group labels alone do not establish that participants were comparable in other characteristics. Eligibility criteria, recruitment details, group-specific baseline characteristics, and methods for controlling confounding are not reported in the registry record. These omissions limit how specifically the study population and the basis for between-group comparisons can be characterized.

The registry lists one primary outcome measure and no statistical analyses. It does not report a protocol-level sample-size justification, planned interim analyses, or a detailed statistical analysis plan. The completed status describes the record’s administrative status; it does not mean that results for the primary outcome are present.

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: Inclusion criteria and indicators for CR were reporting calorie restriction without malnutrition for a minimum of two years, BMI \< 24.99, and fasting glucose \<80 mg/dL.

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 Telomere Length, measured over One day.

The primary endpoint is telomere length, recorded as a ratio and described as a continuous measure summarized by a mean and standard deviation. Telomeres are structures at the ends of chromosomes. In the registry’s description, telomere length is used as a marker of cellular aging: longer telomere length is framed as consistent with less cellular aging. The outcome was assessed from a blood draw on the study day.

The scientific rationale is to ask whether people with long-term caloric restriction have telomere lengths that differ from those in normal-eating and obese comparison groups. Because measurements are taken at one time point, the endpoint represents a cross-sectional group comparison. It does not measure how telomere length changes within a participant over time, and the record does not describe repeated measurements or follow-up.

The registry record does not report the observed mean telomere length, standard deviation, or other group-specific endpoint estimates. It also does not report a comparison estimate or its uncertainty. Therefore, the endpoint’s intended meaning can be described, but the posted record does not show whether the observed measurements support a difference among the groups.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the endpoint as a continuous measure and specifies the mean and standard deviation as its summary statistics. In general, a mean gives the arithmetic average of measured values, while a standard deviation describes how spread out individual measurements are around that average. Reporting both can help readers understand the location and variability of a continuous outcome within a group. The registry record does not report these summaries for telomere length.

What would a group comparison estimate?

In general, a comparison of group means estimates how far apart the average endpoint values are in the groups being compared. The estimate’s units and interpretation depend on the outcome scale; this registry describes telomere length in a ratio. A numerical estimate would need to be read alongside its uncertainty and the analysis methods. No group-comparison estimate is reported in the registry record, so the direction and magnitude of a difference cannot be described.

What does a confidence interval contribute?

In general, a confidence interval communicates the uncertainty around an estimated quantity under the assumptions of the statistical method. It gives a range of values compatible with the data and model at the stated confidence level; it is not a guarantee that the true value lies within that particular interval. A narrow interval indicates greater precision than a wide interval, while the substantive meaning still depends on the outcome scale and the size of the estimate. The registry record does not report a confidence interval for telomere length.

What does a p-value contribute?

In general, a p-value describes how incompatible the observed data are with a specified null model, conditional on that model and its assumptions. It is not the probability that the null hypothesis is true, nor a measure of the size or importance of a difference. It should be interpreted with an effect estimate and uncertainty, not as a stand-alone result. No p-value or statistical comparison is reported in the registry record.

These distinctions matter because an analysis can be statistically compatible with a range of effects, and a small p-value alone would not explain the practical or scientific magnitude of a result. Conversely, a non-significant result would not by itself show that groups are equivalent. Equivalence or non-inferiority requires a specified margin and an appropriate analysis; neither is reported in the registry record.

Why does the study design matter?

In general, random allocation can help balance measured and unmeasured characteristics between treatment groups. This study is described as a cross-sectional comparison of existing groups, with no random allocation stated. Differences between groups could therefore reflect other characteristics as well as their calorie-restriction status. Statistical adjustment can address measured confounders when suitable data and a prespecified approach are available, but cannot automatically remove bias from unmeasured or poorly measured factors. The registry does not report adjusted analyses or the covariates used in any analysis.

Because the endpoint is assessed once, the analysis concerns values at that assessment rather than within-person change. A cross-sectional result cannot establish the order of events or show that group membership caused an outcome difference. In general, repeated measurements and a suitable longitudinal analysis are needed to study change over time; no such follow-up is described in this record.

How should planning calculations be read?

The sample-size assumptions describe planning illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. In general, such calculations ask how many participants per arm would be needed under chosen assumptions to reach a target power for detecting a specified effect. They are not the number of participants observed in the study, and they are not observed power. The record does not provide the observed endpoint estimates needed to verify the effect used in the illustration. The calculations are not evidence that the study was designed with those assumptions or that a particular result was found.

The registry does not report the statistical analysis plan, the approach to missing outcome data, or methods for any multiplicity adjustment. Those details are important for evaluating how comparisons were selected, how incomplete measurements were handled, and how uncertainty was quantified. In their absence, the analysis choices cannot be reconstructed from the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure, telomere length, and no statistical analyses. It does not describe a prespecified analysis plan or report how many statistical comparisons were planned or conducted. The number of listed outcome measures alone does not establish how many group contrasts, subgroups, or other analyses were considered. Multiplicity methods, such as adjustment for multiple comparisons, are not reported in the registry record. It is therefore not possible to determine whether multiplicity was relevant to the reported analysis or how it was handled.

The registry record also does not report missing-data counts or methods. It does not state how many participants had a telomere-length measurement available for analysis, whether any measurements were excluded, or how missing outcome data were treated. The enrollment figure and the risk-group counts in adverse-event reporting do not establish the analytic sample for the primary endpoint.

Analysis populations are not described. The record does not identify an intention-to-treat, per-protocol, or other analytic population, which is relevant in a nonrandomized study as well as in a trial. No participant flow, exclusions, or group-specific endpoint denominators are reported. These omissions prevent assessment of whether endpoint results, if analyzed, would represent all enrolled participants or a selected subset. They also make it difficult to judge the potential influence of missingness or analysis choices on any group comparison.

11. 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 0% reporting threshold.

The adverse-event figures list zero serious adverse events, zero other adverse events, and zero deaths for each of the three groups. The risk counts recorded for these reports are 30 for the Calorie Restricting Group, 16 for Normal-eating Controls, and 25 for the Obese Comparison Group. These are the figures recorded in the registry’s adverse-event data; they are not reported telomere-length analysis counts.

Zero recorded events should be read as a statement about what the registry reports, not as proof that no events occurred outside the scope or methods of that reporting. The record does not describe event definitions, ascertainment methods, reporting duration, or whether the safety data were collected systematically. It also gives no serious adverse event terms. Because the study description says there was a single assessment and no follow-up, these figures should not be interpreted as evidence from long-term safety monitoring. The registry does not provide information that would support a broader safety conclusion.

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

The record establishes that the study was designed to examine a cross-sectional association between long-term caloric restriction and telomere length. It identifies a primary endpoint, describes the one-time blood draw, and names the comparison groups. It does not report the telomere-length measurements or statistical results. Consequently, the record does not establish whether the groups differed, how large any difference was, or how precisely it was estimated.

Even with numerical results, a one-time comparison of nonrandomized groups would support an association, not a causal conclusion that caloric restriction changed telomere length. Participants’ group status was not assigned by the study, and the record does not report methods to address other differences among groups. A cross-sectional assessment also cannot show the course of telomere length over time or establish that a measured difference developed after long-term calorie restriction.

The endpoint has a biological interpretation in the registry: telomere length is used as a marker of cellular aging, with longer length framed as less aging. A marker is not itself a direct measure of every aspect of aging, and the record does not report additional clinical outcomes that would connect this measure to health effects. The endpoint’s rationale should not be mistaken for a demonstrated result.

The appropriate conclusion from the registry record is limited: it describes the question and design, but the primary outcome findings and analysis are not reported. Neither a benefit nor an absence of an association can be inferred from that lack of reporting. Planning illustrations, if considered, describe calculations under assumptions and do not supply missing evidence about the observed endpoint.

13. Why This Trial Matters Statistically

This study is statistically notable because its central question is framed as an association between a long-term dietary pattern and a biomarker measured at one point in time. That makes the distinction between association and causation essential. The group labels describe existing participant categories rather than randomly assigned conditions, so comparison results would need to be interpreted with attention to possible differences among the groups.

The endpoint is continuous, making its estimated group means, variability, and uncertainty central to interpretation. Without those estimates, readers cannot judge the size or precision of any observed difference. A p-value alone, if it were reported, would not resolve that gap; effect estimates and confidence intervals are needed to understand what range of differences is compatible with the data.

The registry also illustrates why registration details and posted results serve different purposes. The description documents the intended question and the measurement approach, while the results fields do not report the endpoint analysis. The completed status and the listed enrollment do not provide the missing outcome estimates. Similarly, sample-size planning illustrations are not a substitute for reporting the actual analysis and should not be read as observed power.

Finally, the study’s single time point places a clear boundary on what it could establish. It can address group differences at the assessment, but cannot show within-person change. These design and reporting distinctions help keep biological rationale, statistical evidence, and causal claims separate.

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 most immediate limitation for interpreting the posted record is that it does not report the primary endpoint results or statistical analyses. Without group-specific telomere-length estimates, uncertainty intervals, or a defined comparison, readers cannot evaluate the direction, magnitude, or precision of an association.

The design is cross-sectional and nonrandomized. Group allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. Potential confounding is therefore a concern in general: characteristics other than calorie-restriction status could be associated with both group membership and telomere length. The registry does not report participant characteristics or adjusted analyses that would show how such differences were addressed.

Measurement at one time point limits interpretation to a cross-sectional association. There is no follow-up described, so the record cannot show change within participants or the temporal development of any group difference. Although the outcome is described as a cellular-aging marker, no additional outcomes are reported that would establish broader health implications.

Further details that would help evaluate the evidence are not reported in the registry record, including eligibility and recruitment information, group-specific endpoint denominators, missing-data handling, the analysis population, and a statistical analysis plan. The registry’s adverse-event figures also lack details about ascertainment and reporting duration. These are limitations of what can be concluded from this record; they do not establish that the study did not collect or analyze information outside the posted registry fields.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Long-term Caloric Restriction and Cellular Aging Markers — NCT01256840.
• Registry record last updated 2017-10-13; status last verified 2017-10.
• Results first posted 2017-10-13.
• 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 Caloric Restriction With Optimal Nutrition and Aging Study is listed as completed, with the University of California, San Francisco as sponsor. The registry reports enrollment of 71 and dates of 2010-12 for study start and 2014-08 for primary completion.

The study description calls it a one-time, cross-sectional assessment rather than a clinical trial. It compares calorie-restricting participants with normal-eating controls and an obese comparison group. The primary outcome is telomere length, described as a ratio and a marker of cellular aging, assessed from a blood draw on the study day.

The registry record does not report the primary outcome estimates or statistical analyses. It also does not report the analysis plan, missing-data methods, or analysis populations. Its adverse-event figures list zero serious adverse events, zero other adverse events, and zero deaths in each group. These figures do not provide the missing endpoint results or establish a broader safety conclusion.