Feasibility and Safety of a Ketogenic Diet During Systemic Therapy for Metastatic Renal Cell Carcinoma: Results from the Cetorein Pilot Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In the manuscript the authors presented a single centered, non-randomized pilot study evaluating the feasibility and safety of a ketogenic diet (KD) administered concurrently with systemic therapy in patients with metastatic renal cell carcinoma (mRCC). The study is appropriately designed as a feasible analysis however; major revisions are required before the manuscript can be accepted for publication. The primary issues relate to clarity of study objectives, over‑interpretation of exploratory findings, statistical framing, and numerous language and formatting errors.

Major Comments:

1. The authors are advised to explicitly state in the abstract and results that all survival and response outcomes are descriptive and exploratory only, and no conclusions on efficacy can be drawn.
2. PD‑L1 analysis is only based on 4 patients with no control group and the changes may reflect immunotherapy or sampling differences (Results section -Page 8, lines 198-203 and Discussion – Page 9, lines 260–265). Hence, the authors are advised not over‑interpreted given very small numbers and rephrase that the observation is hypothesis generating only and cannot be attributed to the ketogenic diet.
3. In Statistical Analysis – Page 4, lines 140–144 and Figures 2–3 – Page 6, lines 167–174, authors used 0Paired t tests are despite small sample sizes and no adjustment for multiple comparisons. Also, the p values are reported without power justification. The authors are advised to clearly frame the statistical analysis are exploratory and not powered for hypothetical testing.
4. Baseline characteristics – Page 4, lines 146-152 and Discussion – Page 9, lines 256–259. Patients differ by treatment line, therapy type and histology and hence a short paragraph should be added in the discussion stating that the heterogeneity of treatments and disease stages limit interpretation of safety and clinical outcomes.
5. Endpoints – Page 4, lines 136-139. “Disease free survival” is an incorrect terminology in metastatic disease. The authors are suggested to replace this term with “progression-free survival (PFS)”.

Minor Comments:

1. Table 2 – Page 6, lines 164-166, shows dietary intake and not adverse events and hence the table title should be corrected.
2. There are some formatting and consistency issues in Table 1. Examples: “Liver 5 23.8)” – missing parenthesis and inconsistency in capitalization and spacing.
3. There are several language and spelling errors which needs to be corrected throughout the manuscript and the authors are advised to proof read again. For example, Introduction – Page 2, line 69 “acetone sering as alternative energetic substrates” instead of “serving”, Figure legend – Page 6, line 167 “apparied T test” instead of “a paired”, Table 5 title – Page 8, line 205 “after exposition to ketogenic diet” instead of “exposure” and Conflicts of Interest – Page 11, line 313 “conflicts of interests” instead of “interest”
4. KD ratio description needs consistency. For example, in Methods Page 4, lines 118-119 and Discussion Page 9, lines 225-226, KD described as 2:1, but later adjusted to 1.5:1 without clear justification upfront.

Author Response

Dear Reviewers,

We sincerely thank the Editor and the Reviewers for their evaluation of our manuscript and for their constructive and insightful comments.

We have revised the manuscript in response to all suggestions. In particular, we clarified the feasibility-oriented nature of the study, tempered the interpretation of exploratory efficacy findings, strengthened the statistical limitations, improved methodological details, corrected formatting and language inconsistencies, and revised several sections for clarity and balance.

All changes have been incorporated into the revised manuscript and are detailed point-by-point below :

Reviewer 1

Major comments

1. The authors are advised to explicitly state in the abstract and results that all survival and response outcomes are descriptive and exploratory only, and no conclusions on efficacy can be drawn.

We agree that the study was designed as a feasibility and safety pilot study and was not powered to evaluate antitumor efficacy. We revised the Abstract, Results, Discussion, and Conclusions sections to explicitly state that all survival and response outcomes are descriptive and exploratory only, and that no conclusions regarding efficacy can be drawn from this non-randomized study.

2. PD L1 analysis is only based on 4 patients with no control group and the changes may reflect immunotherapy or sampling differences (Results section -Page 8, lines 198-203 and Discussion – Page 9, lines 260–265). Hence, the authors are advised not over interpreted given very small numbers and rephrase that the observation is hypothesis generating only and cannot be attributed to the ketogenic diet.

The revised manuscript now clearly states that these observations are hypothesis-generating only and cannot be attributed to the ketogenic diet. We acknowledge that changes in PD-L1 expression may reflect immunotherapy effects, temporal and spatial tumor heterogeneity, sampling variability between biopsy and nephrectomy specimens, or tumor evolution over time.

3. In Statistical Analysis – Page 4, lines 140–144 and Figures 2–3 – Page 6, lines 167–174, authors used 0Paired t tests are despite small sample sizes and no adjustment for multiple comparisons. Also, the p values are reported without power justification. The authors are advised to clearly frame the statistical analysis are exploratory and not powered for hypothetical testing.

We revised the Statistical Analysis section to clarify that all statistical analyses were exploratory and not powered for formal hypothesis testing. We specified that, given the pilot nature of the study and the limited sample size, no correction for multiple comparisons was applied and p-values should be interpreted cautiously. We also clarified that normality assumptions were assessed before using paired comparisons and that the results should be considered descriptive.

4. Baseline characteristics – Page 4, lines 146-152 and Discussion – Page 9, lines 256–259. Patients differ by treatment line, therapy type and histology and hence a short paragraph should be added in the discussion stating that the heterogeneity of treatments and disease stages limit interpretation of safety and clinical outcomes.

We added a dedicated paragraph in the Discussion section acknowledging that heterogeneity in treatment regimens, treatment lines, histological subtypes, and disease characteristics limits interpretation of both safety and clinical outcomes.

5. Endpoints – Page 4, lines 136-139. “Disease free survival” is an incorrect terminology in metastatic disease. The authors are suggested to replace this term with “progression-free survival (PFS)”.

“Disease-free survival” has been replaced throughout the manuscript with “progression-free survival (PFS).”

Minor comments

1. Table 2 – Page 6, lines 164-166, shows dietary intake and not adverse events and hence the table title should be corrected.

The title of Table 2 has been corrected to « Composition of diet before and during protocol according to food diary ».

2. There are some formatting and consistency issues in Table 1. Examples: “Liver 5 23.8)” – missing parenthesis and inconsistency in capitalization and spacing.

We revised and corrected Table 1.

3. There are several language and spelling errors which needs to be corrected throughout the manuscript and the authors are advised to proof read again. For example, Introduction – Page 2, line 69 “acetone sering as alternative energetic substrates” instead of “serving”, Figure legend – Page 6, line 167 “apparied T test” instead of “a paired”, Table 5 title – Page 8, line 205 “after exposition to ketogenic diet” instead of “exposure” and Conflicts of Interest – Page 11, line 313 “conflicts of interests” instead of “interest”

The manuscript has been revised and corrected.

4. KD ratio description needs consistency. For example, in Methods Page 4, lines 118-119 and Discussion Page 9, lines 225-226, KD described as 2:1, but later adjusted to 1.5:1 without clear justification upfront.

The manuscript has been revised to explain more explicitly that the planned intervention consisted of a 2:1 ketogenic diet; however, in practice, many patients required adjustment toward a lower ketogenic ratio (approximately 1.5:1) to maintain acceptable tolerability and adequate protein intake.

 

Sincerely,

Cyrielle ROLLEY

On behalf of all co-authors

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addresses a clinically relevant and timely topic: the feasibility and safety of a ketogenic diet in patients with metastatic renal cell carcinoma receiving systemic therapy. The rationale is convincing, since renal cell carcinoma is strongly characterized by metabolic reprogramming, inflammatory remodeling, and immune–metabolic interactions. The study is also valuable because many oncology patients independently adopt restrictive dietary strategies despite the lack of robust clinical evidence. In this context, a prospective pilot experience focused on tolerability, adherence, metabolic monitoring, and preliminary oncological outcomes is of clear interest for the readership of Nutrients.

Overall, the manuscript is well structured and scientifically meaningful. The introduction provides an adequate background on renal cell carcinoma, systemic therapy, metabolic vulnerability, and the theoretical rationale for ketogenic interventions. However, the authors should slightly refine the introduction to avoid an overly mechanistic tone that could suggest an expected antitumor effect. Since the study is feasibility-oriented, the rationale should remain balanced and clearly state that the ketogenic diet is being explored as a supportive metabolic intervention rather than as an established anticancer strategy. In this section, the authors should also expand the immunological rationale by discussing more explicitly how ketone bodies may influence inflammatory signaling, immune activation, and systemic immunometabolic responses. In this regard, the authors are encouraged to consider citing the following recent review, which would fit well in the introduction or early discussion when describing the immunomodulatory potential of ketogenic interventions: Monda A,et al., Exploring the ketogenic diet’s potential in reducing neuroinflammation and modulating immune responses. Frontiers in Immunology. 2024;15:1425816. doi:10.3389/fimmu.2024.1425816. Although this article is not focused on renal cell carcinoma, it provides a useful mechanistic framework on ketone bodies, inflammatory pathways, immune modulation, and the role of β-hydroxybutyrate, which could strengthen the biological interpretation of the present study.

The methods are generally clear, but several details should be improved. The manuscript should specify more precisely how caloric targets were calculated, whether protein intake was individualized according to body weight, renal function, nutritional status, or cancer-related risk of sarcopenia, and how dietary counseling was adapted in patients experiencing anorexia, diarrhea, or weight loss. The exclusion criteria are described rather broadly; the authors should define what was considered a contraindication to the ketogenic diet. Given the oncological population, it would also be useful to report whether baseline nutritional risk, sarcopenia, recent unintentional weight loss, or cachexia criteria were assessed. These elements are particularly important because tolerability and adherence are central endpoints.

The definition of the primary endpoint requires clarification. Feasibility is defined by diet-related adverse events, but feasibility usually also includes acceptability, adherence, retention, completion rate, and protocol compliance. The authors should either broaden the definition of feasibility or clearly separate feasibility, safety, and adherence as distinct endpoints. In addition, the attribution of adverse events to the ketogenic diet versus systemic therapy is challenging in this clinical setting. The manuscript would benefit from a short explanation of how causality was assessed and whether adverse events were adjudicated by the oncology team, the nutrition team, or both.

The statistical analysis is acceptable for a pilot study, but it needs more detail and caution. Given the very small sample size and repeated measurements over time with substantial attrition, the use of multiple pairwise comparisons should be described carefully. The authors should specify whether normality was assessed before using paired t-tests, whether non-parametric alternatives were considered, and whether any correction for multiple testing was applied. For repeated longitudinal variables such as weight, cholesterol, triglycerides, creatinine, and micronutrients, a mixed-effects model would theoretically be more appropriate, although the sample size may limit its use. At minimum, the authors should acknowledge that the analyses are exploratory and underpowered. Survival analyses should be presented descriptively; Cox regression is mentioned, but it is unclear which covariates were entered and whether the number of events was sufficient. If no meaningful Cox model was performed, this should be removed or clarified.

The results are interesting and generally coherent with the feasibility aim. However, presentation should be improved. The flow of patients needs to be clearer, especially because 21 patients were enrolled, 20 appear to have started the diet, and the denominators vary across tables and time points. The authors should consistently report denominators for each analysis. The completion rate of 40% is clinically informative, but the reasons for discontinuation should be presented with more precision, distinguishing intolerance, systemic treatment toxicity, disease progression, and patient preference. The macronutrient data are useful, but the ketogenic ratio achieved appears lower than the planned 2:1 ratio; this point should be emphasized as a relevant feasibility finding rather than a minor detail. The authors should also clarify how urinary ketone levels were categorized and whether blood β-hydroxybutyrate was considered or unavailable.

The safety data are clinically relevant, particularly the gastrointestinal intolerance, lipid profile changes, weight loss, and renal function trends. However, some inconsistencies should be corrected. The numbering and titles of Tables 2, 3, and 4 appear confused, and the table captions should accurately match the content. There are also typographical errors such as “apparied T-test,” which should be corrected to “paired t-test.” The adverse-event table should distinguish all-grade, grade 1–2, and grade 3–4 events more clearly. For dyspepsia, the reported percentage appears inconsistent and should be checked. The authors should also comment more carefully on the clinical meaning of increased cholesterol and creatinine during follow-up, even if these changes are expected or influenced by attrition.

The efficacy section should be toned down. The observed response rates, progression-free survival, and overall survival are descriptive and cannot be attributed to the ketogenic diet. The authors already acknowledge this limitation, but the results and abstract should avoid any wording that could imply efficacy. The PD-L1 exploratory analysis is intriguing but extremely limited. Since only four patients were evaluated, and because biopsies and nephrectomy specimens may differ spatially and temporally, the interpretation should be very cautious. The authors should explicitly state that changes in PD-L1 expression may reflect treatment effects, sampling heterogeneity, tumor evolution, or methodological variability, and cannot be attributed to diet.

The discussion is balanced and clinically sensible. Its strongest point is the practical interpretation that a 12-month ketogenic intervention is difficult to sustain in metastatic cancer patients and that a shorter, more flexible protocol may be preferable. This is an important contribution. Nevertheless, the discussion could be strengthened by linking the clinical tolerability findings with the biological rationale. For example, the authors could explain that although ketogenic diets may theoretically influence inflammatory and immune pathways, real-world feasibility, nutritional safety, and preservation of lean mass are decisive issues in advanced cancer. The suggested citation by Monda et al. would be useful here to support a more nuanced discussion of ketone bodies as immunometabolic mediators rather than purely energetic substrates.

The bibliography is generally appropriate and updated, including recent epidemiological data, renal cell carcinoma guidelines, dietary-intervention literature, and ketogenic diet studies in oncology. However, the reference list should be checked carefully for formatting consistency. Some references appear very recent and relevant, but the authors should ensure that all in-text citations are included in the reference list and that the journal style is applied uniformly. The addition of the Monda et al. 2024 review would enrich the mechanistic and immunological background, especially where the manuscript discusses systemic inflammation, immune modulation, and the possible biological effects of ketogenic metabolism.

The English is generally understandable and scientifically adequate, but the manuscript requires language polishing. Several sentences are slightly awkward or contain minor grammatical errors, including “serving” misspelled, missing punctuation, inconsistent capitalization in table titles, and occasional imprecise expressions. The authors should revise the manuscript for style, grammar, and consistency, particularly in the abstract, figure legends, table captions, and discussion. The use of abbreviations should also be standardized throughout the text.

In conclusion, this is a valuable pilot study that provides useful preliminary evidence on the feasibility and safety of a ketogenic diet in selected patients with metastatic renal cell carcinoma receiving systemic therapy. The study is limited by its small sample size, non-randomized design, absence of a control group, attrition, and exploratory biological analyses, but these limitations are acceptable for a feasibility study if clearly stated and carefully interpreted. The manuscript should be revised to improve methodological clarity, statistical transparency, consistency of tables and figures, cautious interpretation of efficacy and PD-L1 findings, and integration of relevant literature on ketogenic diet–related immunomodulation.

Author Response

Dear Reviewers,

We sincerely thank the Editor and the Reviewers for their evaluation of our manuscript and for their constructive and insightful comments.

We have revised the manuscript in response to all suggestions. In particular, we clarified the feasibility-oriented nature of the study, tempered the interpretation of exploratory efficacy findings, strengthened the statistical limitations, improved methodological details, corrected formatting and language inconsistencies, and revised several sections for clarity and balance.

All changes have been incorporated into the revised manuscript and are detailed point-by-point below :

1. Expected antitumor effect

We added the recommended reference in the manuscript, in the Introduction and Discussion sections to strengthen the description of the immunomodulatory and inflammatory effects of ketone bodies and ketogenic interventions .

2. Nutritional details

Additional methodological details were added regarding caloric target determination, dietary counseling, and adaptation of the ketogenic protocol in patients experiencing anorexia, gastrointestinal toxicity, or weight loss.

3. Contraindications

The exclusion criteria section has been expanded to clarify contraindications to ketogenic diet implementation. We also added clarification regarding baseline nutritional assessment and the clinical consideration of malnutrition and cachexia risk during patient selection and follow-up.

4. Feasibility definition

The manuscript has been revised to better distinguish feasibility, safety, adherence, retention, and completion rate as complementary endpoints of this pilot study.

5. Causality assessment adverse events

We clarified that attribution of adverse events to ketogenic diet versus systemic therapy was assessed jointly by the oncology and nutrition teams based on clinical evaluation and temporal association.

6. Statistical analysis

We specified that normality of continuous variables was assessed before using paired t-tests. When the distribution was not considered appropriate for parametric testing, non-parametric alternatives were considered.

We clarified that no formal correction for multiple testing was applied because of the exploratory nature of this pilot feasibility study. This point has now been explicitly acknowledged in the manuscript.

We agree that mixed-effects models would theoretically represent a more robust approach for repeated longitudinal measurements. However, given the limited sample size and the progressive reduction in evaluable patients over time, we considered that such models would not provide reliable estimates in this dataset. We therefore chose to present descriptive longitudinal analyses with simple paired comparisons, while emphasizing their exploratory character and limited statistical power.

We added a statement in the discussion acknowledging that the study was not powered for inferential longitudinal analyses and that all secondary biological analyses should be interpreted cautiously.

Regarding survival analyses, we clarified that these analyses were descriptive only. Although Cox regression had initially been considered, the very limited number of patients and events did not allow meaningful multivariable modeling. Consequently, references suggesting a formal Cox proportional hazards analysis have been removed/clarified in the revised manuscript.

We believe these modifications improve the transparency and methodological rigor of the manuscript while remaining consistent with the pilot nature of the study.

7. Results section

We clarified that although 21 patients were enrolled, one patient discontinued before effective ketogenic diet initiation, resulting in 20 evaluable patients for dietary analyses.

We revised the description of ketogenic diet discontinuation to better distinguish discontinuations related to disease progression, intolerance to the ketogenic diet or systemic treatment toxicity.

We clarified the methodology for ketone monitoring.

8. PD-L1 exploratory analysis

The revised manuscript now clearly states that these observations are hypothesis-generating only and cannot be attributed to the ketogenic diet. We acknowledge that changes in PD-L1 expression may reflect immunotherapy effects, temporal and spatial tumor heterogeneity, sampling variability between biopsy and nephrectomy specimens, or tumor evolution over time.

9. Safety data

We corrected the Adverse events table.

Discussion section was expanded to provide a more cautious interpretation of the observed increases in cholesterol and creatinine levels during follow-up.

10. References

We revised the references and included Monda et al. 2024.

 

The manuscript has been revised and corrected for inconsisyencies and typographical errors.

 

Sincerely,

Cyrielle ROLLEY

On behalf of all co-authors

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

 

The authors have satisfactorily addressed the major concerns raised in the previous review. In particular:

• The manuscript now appropriately frames all efficacy and survival outcomes as descriptive and exploratory
• The PD-L1 analysis is correctly presented as hypothesis-generating only
• Statistical analyses are clearly described as exploratory and underpowered
• Key limitations, including heterogeneity of the study population, are adequately acknowledged

These revisions significantly improve the scientific rigor and interpretation of the study, and the manuscript is now suitable for publication as a pilot feasibility study.

However, a few minor but important clarifications are still needed:

1. The description of the ketogenic diet requires clarification. While a 2:1 ratio is described in the Methods, most patients appear to have followed a lower ratio (~1.5:1). The authors should explicitly state whether such adjustments were predefined or introduced post hoc.
2. Given the exploratory nature of the study, the emphasis on p-values and statistical significance in figures should be minimized.
3. Reporting of survival and response outcomes should remain clearly framed as descriptive to avoid misinterpretation.
4. The statement that the ketogenic diet is “safe” should be slightly tempered, given adherence challenges and the observed rate of adverse events.

 

 

Author Response

Dear Reviewer,

We thank the reviewer for this pertinent remark and revised the wording throughout the manuscript.

All changes have been incorporated into the revised manuscript and are detailed point-by-point below:

Reviewer 1

1. The description of the ketogenic diet requires clarification. While a 2:1 ratio is described in the Methods, most patients appear to have followed a lower ratio (~1.5:1). The authors should explicitly state whether such adjustments were predefined or introduced post hoc.

We thank the reviewer for this important comment and agree that clarification was needed regarding the ketogenic ratio achieved during follow-up.

We revised the Methods and Results sections to clarify that the initial study protocol targeted a 2:1 ketogenic ratio (fat to combined protein and carbohydrates). However, individualized dietary adaptations were prospectively allowed according to nutritional status, body weight, and tolerance to systemic treatment. In particular, lower ketogenic ratios could be implemented in obese or nutritionally vulnerable patients to preserve adequate protein intake and maintain lean body mass.

In routine clinical practice, strict maintenance of a 2:1 ratio proved difficult in this metastatic cancer population, and dietary adjustments were frequently necessary to improve tolerability, nutritional safety, and long-term adherence. We therefore clarified that the 2:1 ratio should be considered a therapeutic target rather than a ratio consistently achieved throughout follow-up.

These modifications have been added to the revised manuscript.

2. Given the exploratory nature of the study, the emphasis on p-values and statistical significance in figures should be minimized.

We thank the reviewer for this important methodological comment and agree that, given the exploratory nature of this pilot study and the limited sample size, formal hypothesis-testing interpretations should remain cautious.

Accordingly, we revised the Statistical Analysis section to further emphasize the descriptive and exploratory nature of all analyses. We also modified the Results section to present longitudinal changes in a more descriptive manner rather than focusing on statistical significance.

In addition, we removed significance indicators (p-values and asterisks) from the figures in order to avoid overemphasizing hypothesis-testing results in this exploratory setting.

These modifications were made to better align the presentation of the data with the pilot feasibility objectives of the study.

3. Reporting of survival and response outcomes should remain clearly framed as descriptive to avoid misinterpretation

Survival and tumor response outcomes are now explicitly presented as descriptive exploratory findings that cannot be attributed to the ketogenic intervention. We modified the Results, and Discussion sections to avoid any wording that could imply treatment efficacy or causal interpretation.

 

4. The statement that the ketogenic diet is “safe” should be slightly tempered, given adherence challenges and the observed rate of adverse events.

The term “safe” has been replaced with more cautious expressions such as “acceptable tolerability profile”. We also strengthened the Discussion section to better acknowledge the challenges related to long-term adherence, gastrointestinal adverse events and nutritional monitoring.

 

Sincerely,

Cyrielle ROLLEY

On behalf of all co-authors

Reviewer 2 Report

Comments and Suggestions for Authors

No further comments.

Author Response

We thank the reviewer for the careful evaluation of our manuscript and for the absence of further comments