This study was a randomized, double-blind, placebo-controlled, cross-over trial investigating the effects of carrageenan on insulin resistance and related metabolic parameters in 20 young, non-obese men (mean age 27.4 ± 4.3 years, mean BMI 24.5 ± 2.5 kg/m2). Participants received either 250mg of carrageenan or a placebo twice daily for two weeks, with a washout period of 21-35 days between treatments. The primary outcomes were insulin sensitivity assessed by OGTT and hyperinsulinemic-euglycemic clamp. No significant differences were found between carrageenan and placebo for OGTT-based insulin sensitivity (p=0.52) or clamp-based insulin sensitivity (p=0.52). Secondary outcomes included hepatic insulin sensitivity, brain insulin sensitivity, hypothalamic inflammation, and hepatic triglyceride content, which also did not differ significantly between treatments. A significant interaction effect was found between BMI and treatment, with higher BMI associated with lower whole-body insulin sensitivity during the OGTT (p=0.04) and higher insulin resistance (HOMA2-IR; p=0.01) during carrageenan exposure. Carrageenan exposure significantly increased intestinal permeability, as measured by the lactulose-mannitol ratio (p=0.03) and plasma zonulin levels (placebo: 52.1 ng/l, carrageenan: 55.9 ng/l, p=0.05). In vitro assays demonstrated that carrageenan triggered the activation of CD19+ B cells and CD56+ NK cells and induced the production of pro-inflammatory cytokines (IL-6, IL-13, IL-17, TNF-beta, and GMCSF) in PBMCs.
This randomized, double-blind, placebo-controlled, cross-over trial in 20 young, non-obese men found that short-term carrageenan exposure (250mg twice daily for two weeks) did not significantly affect overall insulin sensitivity, measured by OGTT (p=0.52) and hyperinsulinemic-euglycemic clamp (p=0.52). However, a significant interaction between BMI and treatment was observed, with higher BMI associated with lower whole-body insulin sensitivity (OGTT, p=0.04), higher insulin resistance (HOMA2-IR, p=0.01), and a trend toward higher hypothalamic inflammation during carrageenan exposure. Carrageenan also significantly increased intestinal permeability, as measured by the lactulose-mannitol ratio (p=0.03) and plasma zonulin levels (p=0.05). These findings suggest a potential population impact where carrageenan may exacerbate metabolic dysfunction in individuals with higher BMI, potentially through mechanisms involving increased gut permeability and inflammation.
The study's findings suggest that implementation of dietary guidelines may need to consider the potential adverse effects of carrageenan, particularly in individuals with higher BMI. While the study did not directly assess dietary intake, the results suggest that reducing carrageenan consumption, especially in processed foods, could be a beneficial strategy for individuals at risk of metabolic disorders. This would require resources for public health education and potentially food labeling regulations.
There are uncertainties regarding the long-term effects of carrageenan exposure and the specific thresholds of BMI at which the adverse effects become clinically significant. The study's findings suggest a potential risk of increased insulin resistance and inflammation in individuals with higher BMI, but the benefits of avoiding carrageenan need to be weighed against the potential costs and challenges of altering dietary habits. Subgroup considerations are crucial, as the study suggests that the effects of carrageenan may be more pronounced in individuals with pre-existing metabolic vulnerability.
Key knowledge gaps remain regarding the long-term effects of carrageenan consumption, the specific mechanisms underlying the BMI-dependent effects, and the role of the gut microbiome. The study's limitations, including the small sample size, the recruitment of only young, healthy males, and the short exposure period, may underestimate the true effect size of carrageenan in a broader population. Future research should focus on larger, more diverse populations, longer exposure periods, and a more detailed investigation of the gut microbiome's role. Clinically, the findings suggest a need for caution regarding carrageenan intake, particularly in individuals with higher BMI, and highlight the importance of further research to inform dietary recommendations.
The abstract clearly states the research question, focusing on the impact of carrageenan, a common food additive, on insulin resistance and related metabolic parameters in humans.
The abstract concisely summarizes the study design, including the key methodological details such as the randomized, double-blind, placebo-controlled, cross-over design, participant characteristics, and intervention.
The abstract presents the main findings, including both the overall lack of significant difference in insulin sensitivity and the interaction effect observed between BMI and treatment.
The abstract highlights the key conclusion, suggesting a potential contribution of carrageenan to insulin resistance and subclinical inflammation in overweight individuals.
This is a high-impact improvement that would enhance the abstract's informativeness and impact. Abstracts serve as a critical entry point for readers, and explicitly stating the directionality of the BMI interaction effect provides immediate clarity regarding the study's core finding. This is crucial for researchers quickly assessing the relevance of the work.
Implementation: Specify the direction of the BMI interaction. For example, instead of just stating "interactions between BMI and treatment were observed," state "interactions between BMI and treatment were observed, with higher BMI associated with lower insulin sensitivity during carrageenan exposure."
This medium-impact change would improve the abstract's completeness and clinical relevance. Abstracts should concisely cover all key aspects of the study. While the abstract mentions increased intestinal permeability, it does not explicitly link this to the overall conclusion. Connecting this finding strengthens the mechanistic explanation for carrageenan's potential effects.
Implementation: Explicitly connect the finding of increased intestinal permeability to the overall conclusion. Add a phrase such as, "...through pro-inflammatory mechanisms in the gut, as evidenced by increased intestinal permeability."
This medium-impact change would increase the abstract's precision and quantitative information content. Abstracts should provide key quantitative results whenever possible. Including the mean BMI and its standard deviation (or range) gives a more precise picture of the participant group where the interaction effect was observed.
Implementation: Include the mean BMI and standard deviation (or range) for the overweight subgroup where the significant interaction was found, not just the overall group. This could be added parenthetically after "In overweight participants..." or in a separate sentence.
This is a low-impact improvement, but would improve the abstract's clarity and flow. The current wording is slightly repetitive. Streamlining this phrase enhances readability without losing meaning.
Implementation: Change "Further investigation into the long‑term health impacts of carrageenan and other food additives is warranted." to "Further investigation into the long-term health impacts of carrageenan and similar food additives is warranted." or "Long-term health impacts of carrageenan and other food additives warrant further investigation."
The background section clearly and concisely introduces the public health context, highlighting the global rise in type 2 diabetes and its connection to the 'Western-style' diet, characterized by ultra-processed foods.
The section effectively introduces carrageenan, describing its widespread use in the food industry, its chemical structure, and the distinction between high molecular-weight carrageenan and poligeenans.
The section succinctly summarizes existing evidence from animal and epidemiological studies, highlighting the potential negative effects of carrageenan on glucose metabolism and inflammation, and establishing the knowledge gap that the current study aims to address.
This is a medium-impact improvement that would enhance the Background section's completeness and strengthen the rationale for the study. While the section mentions the increasing prevalence of diabetes, it doesn't explicitly connect this to the increasing consumption of ultra-processed foods and, consequently, carrageenan. The Background section's role is to build a compelling case for the research; connecting these trends strengthens that case.
Implementation: Add a sentence explicitly linking the rise in diabetes prevalence to the increasing consumption of ultra-processed foods and carrageenan. For example: "This increasing diabetes prevalence parallels the growing consumption of ultra-processed foods, and consequently, food additives like carrageenan."
This is a medium-impact improvement that would provide crucial context for interpreting the study's findings and their significance. The Background section should provide all necessary context. While the section mentions the increase in carrageenan intake, it doesn't provide a clear sense of what constitutes a 'high' intake in the context of a typical Western diet. This makes it difficult to assess the relevance of the study's intervention dose (250mg twice daily).
Implementation: Provide a range or estimate of typical daily carrageenan intake in Western diets, if available. This could be added after the sentence mentioning the increase in intake. For example, "...in some countries [3]. Current estimates suggest average daily intakes ranging from X to Y mg in Western diets."
This is a low-impact improvement, but it would improve the Background section's clarity and flow. The current wording is slightly repetitive and could be streamlined.
Implementation: Change "It is unknown if other dietary components of a Western-style diet also play a role in this process." to "The role of other dietary components of a Western-style diet in this process is also unknown." or "The contribution of other dietary components of a Western-style diet remains unclear."
The Methods section clearly describes the study design as a placebo-controlled, randomized, double-blind, cross-over trial. This design is appropriate for the research question and minimizes bias.
The section provides clear inclusion and exclusion criteria for participants, ensuring a homogenous study population and reducing confounding factors. This enhances the internal validity of the study.
The study used both OGTT and hyperinsulinemic-euglycemic clamp to assess insulin sensitivity. The hyperinsulinemic-euglycemic clamp is considered the gold standard for measuring insulin sensitivity, adding to the study's methodological rigor.
The Methods section clearly outlines the intervention protocol, including the dosage and administration of carrageenan and placebo. This level of detail enhances the reproducibility of the study.
The study includes a comprehensive range of outcome measures, including not only insulin sensitivity but also hepatic insulin sensitivity, brain inflammation, intestinal permeability, and gut microbiome composition. This allows for a more complete understanding of carrageenan's potential effects.
This is a medium-impact improvement that would enhance the study's methodological transparency and reproducibility. The Methods section needs to specify the type of carrageenan used. Different types of carrageenan (kappa, iota, lambda) have different gelling properties and potentially different biological effects. This detail is crucial for interpreting the results and for other researchers attempting to replicate the study.
Implementation: Specify the type of carrageenan used (kappa, iota, or lambda). This could be added to the 'Intervention' section. For example: "Carrageenan (E 407, kappa-carrageenan) was purchased...". If the specific type is unknown, state that, but also state any known properties (e.g., gelling strength in water and milk) that might provide clues.
This is a medium-impact improvement that would strengthen the study's methodological rigor and address a potential source of bias. The Methods section should state whether compliance with the intervention was assessed and, if so, how. Knowing whether participants actually took the capsules as prescribed is crucial for interpreting the results. Without this, it's difficult to know if negative findings are due to a lack of effect of carrageenan or simply poor adherence to the protocol.
Implementation: Add a statement about how participant compliance with the intervention was assessed. This could be added to the 'Intervention' or 'Diagnostic procedures' section. Examples include: "Participant compliance was assessed by capsule counts at each visit." or "Participants were asked to keep a diary of capsule intake." or "Compliance was not formally assessed."
This is a low-impact improvement, but it would improve the clarity and completeness of the Methods section. While the section mentions blinding, it doesn't explicitly state who was blinded. The Methods section needs to be explicit about all aspects of the study design. Confirming that participants, investigators, and those assessing the outcomes were blinded strengthens the study's internal validity.
Implementation: Explicitly state who was blinded to the intervention. This can be added to the 'Trial design and participants' section. For example: "Participants, investigators, and those assessing the outcomes were blinded to the assignment of interventions."
This is a medium-impact improvement that would enhance the study's transparency and reproducibility. The Methods section needs more detail on the statistical analysis plan. The Methods section should provide enough detail about the statistical methods to allow for replication and evaluation of the appropriateness of the chosen analyses. While some statistical methods are mentioned, key details are missing.
Implementation: Provide more detail on the statistical analysis plan, including: (1) The specific statistical test used for the primary outcome (Matsuda index and M-value). (2) How carry-over effects were assessed. (3) How missing data were handled (if any). (4) Software used for statistical analysis. (5) Justification for the chosen sample size.
This is a low-impact improvement that would increase the clarity and completeness of the Methods section. The Methods section should state the manufacturer and model of the equipment used for key measurements, such as the MRI scanner and the glucometer. This enhances reproducibility and allows for comparison with other studies.
Implementation: Add the manufacturer and model of the MRI scanner and glucometer. For example: "Whole-brain MRI was obtained by using a 3 Tesla scanner (Siemens PRISMA, Siemens Healthineers, Erlangen, Germany) with a 20-channel head coil." and "Plasma glucose levels were measured with a glucometer (EKF, Germany, model: Biosen C-line)"
The Results section clearly presents the main findings of the study, stating that overall insulin sensitivity did not differ significantly between the carrageenan and placebo treatments. This direct presentation of the primary outcome is crucial for a Results section.
The section reports the results of key secondary outcomes, including hepatic insulin sensitivity, brain insulin sensitivity, hypothalamic inflammation, and hepatic triglyceride content. This comprehensive reporting allows for a thorough evaluation of carrageenan's potential effects.
The Results section highlights the significant finding of increased intestinal permeability, measured by the lactulose-mannitol ratio, during carrageenan exposure. This finding is important for understanding the potential mechanisms of carrageenan's effects.
The section presents the post hoc analysis showing higher plasma zonulin levels after carrageenan exposure, further supporting the finding of increased intestinal permeability. This additional evidence strengthens the study's conclusions.
The Results section reports the interaction analyses between BMI and treatment, revealing lower whole-body and hepatic insulin sensitivity, and higher insulin resistance with higher BMI during carrageenan exposure. This is a key finding that modifies the interpretation of the primary outcome.
The section includes results from in vitro assays showing carrageenan-induced activation of immune cells and cytokine production. This provides further mechanistic insight into carrageenan's potential effects.
The section appropriately uses figures to visually represent the data, making it easier for readers to understand the results. The figures include box plots and interaction plots, which are suitable for the type of data presented.
This is a high-impact improvement that is crucial for the clarity and interpretability of the Results section. The Results section must provide the actual values (means and standard deviations/errors) for the primary and secondary outcomes, not just p-values. Currently, the reader only knows whether there was a statistically significant difference, but not the magnitude or direction of any effect (or lack thereof). This is essential for assessing the clinical relevance of the findings and for comparing the results to other studies.
Implementation: Include the mean and standard deviation (or standard error) for each outcome measure in each treatment group (placebo and carrageenan). This can be done in the text, in a table (Table S2 is referenced, but doesn't contain all outcomes), or in the figure legends. For example, instead of just stating "None of these variables showed differences between treatments (n = 20 pairs for the OGTT and n = 19 pairs for clamp, p = 0.52 for both, Fig. 1A, B)", report: "Mean (SD) OGTT-based insulin sensitivity was X (Y) in the placebo group and A (B) in the carrageenan group (p = 0.52)."
This is a high-impact improvement necessary for the completeness and accuracy of the Results section. The Results section must report the results of the statistical tests for carry-over effects. The Methods section states that carry-over effects were tested, but the Results section only states "No carry-over effects were detected (p > 0.05)." This is insufficient. The actual p-values (or a statement that all p-values were above a specific threshold, e.g., p > 0.10) for each outcome tested for carry-over effects must be reported. This is crucial for assessing the validity of the cross-over design.
Implementation: Report the results of the statistical tests for carry-over effects for each outcome. This can be done in the text or in a supplementary table. For example: "Carry-over effects were assessed for all outcomes; no significant carry-over effects were detected (all p > 0.10)." or "Carry-over effects were assessed; p-values for carry-over tests are reported in Supplementary Table X."
This is a medium-impact improvement that would enhance the clarity and completeness of the Results section. The Results section should briefly describe the gut microbiome analysis results, even if no significant differences were found. The Methods section describes a detailed microbiome analysis, and the Results section should summarize the findings, even if negative. This is important for transparency and for providing a complete picture of the study's findings.
Implementation: Add a brief paragraph summarizing the gut microbiome analysis results. For example: "Gut microbiome composition was analyzed using whole-genome sequencing. No significant differences in overall microbiome composition or specific taxa were observed between the placebo and carrageenan treatments (data not shown)." or refer to supplementary material if the data is presented there.
This is a low-impact improvement that would enhance the clarity of the Results section. The Results section should consistently use either "N" or "n" to represent sample size, not both. The current section uses both "N" and "n" interchangeably, which can be confusing for the reader.
Implementation: Choose either "N" or "n" to represent sample size and use it consistently throughout the Results section. It's generally recommended to use lowercase "n" for sample size.
This is a low-impact improvement that would improve the clarity of the Results section. The Results section should define the abbreviations used in the figures the first time they are used. The current section uses abbreviations like "PCB" and "CGN" without defining them in the text. While these are defined in the figure legends, it's best practice to also define them in the text when they first appear.
Implementation: Define the abbreviations "PCB" and "CGN" the first time they are used in the Results section. For example: "...after placebo (PCB) and carrageenan (CGN) administration...".
Fig. 1 A-C Differences in whole-body insulin sensitivity (A) and organ-related insulin sensitivity (predominantly skeletal muscle (B), liver (C)) after placebo (PCB) and carrageenan (CGN) administration in the study.
Fig. 2 A, B Intestinal permeability expressed by lactulose-mannitol ratio (A) and plasma zonulin levels (B) after treatments with placebo (PCB) and carrageenan (CGN).
Fig. 3 A-F Interaction between BMI and treatment (placebo-PCB, carrageenan-CGN) on predefined study endpoints.
Fig. 4 A, B In vitro analysis of peripheral blood mononuclear cells (PBMCs) from 15 healthy individuals before carrageenan exposure.
Figure S3 Interindividual diversity in stool microbiome samples obscures any potential impact of carrageen use on the composition of the gut microbiome.
The Discussion section effectively summarizes the main findings of the study, reiterating the lack of overall effect on insulin sensitivity and the significant interaction with BMI.
The section appropriately places the findings in the context of existing literature, citing relevant studies on carrageenan's effects in animal models and humans.
The Discussion section explores potential mechanisms underlying the observed effects, focusing on increased intestinal permeability and inflammation.
The section acknowledges the limitations of the study, including the recruitment of only young, healthy males and the relatively short exposure periods.
The Discussion section appropriately connects the findings to broader implications, suggesting caution with carrageenan-containing foods, especially in individuals prone to developing type 2 diabetes.
This is a high-impact improvement that would strengthen the Discussion section's interpretation of the findings and their implications. The Discussion section should more explicitly discuss the discrepancy between the lack of overall effect on insulin sensitivity and the significant interaction with BMI. Currently, these two findings are presented, but not fully reconciled. A more thorough discussion of why carrageenan might affect insulin sensitivity only in individuals with higher BMI is needed. This is a missed opportunity to provide a more nuanced and insightful interpretation.
Implementation: Add a paragraph (or expand an existing one) to explicitly discuss the discrepancy between the overall null effect and the BMI interaction. Consider including: (1) Possible explanations for why BMI might modify the effect of carrageenan (e.g., pre-existing subclinical inflammation, differences in gut microbiome composition). (2) Whether this finding aligns with or contradicts previous research. (3) The implications of this finding for future research and public health recommendations.
This is a medium-impact improvement that would enhance the Discussion section's depth and provide a more comprehensive mechanistic explanation. The Discussion section should elaborate on the potential role of the gut microbiome in mediating the effects of carrageenan. While the section mentions that carrageenan-related alterations of gut microbiome composition were tested, it doesn't fully explore the potential for microbiome interactions, even in the absence of significant overall compositional changes. Given the known importance of the gut microbiome in metabolic health and inflammation, this is a missed opportunity.
Implementation: Expand the discussion of the gut microbiome, even though no significant overall changes were observed. Consider including: (1) The possibility of subtle microbiome changes (e.g., functional changes, changes in specific low-abundance taxa) that were not detected by the analysis. (2) The potential for carrageenan to interact with pre-existing microbiome differences to influence its effects (e.g., individuals with higher BMI might have a different baseline microbiome that is more susceptible to carrageenan's effects). (3) Reference to relevant literature on the role of the gut microbiome in mediating the effects of dietary factors on metabolic health.
This is a medium-impact improvement that would strengthen the Discussion section's interpretation and its connection to clinical relevance. The Discussion section should more directly address the clinical significance of the observed increase in intestinal permeability. While the section describes the mechanisms of intestinal permeability and its connection to leaky gut syndrome, it doesn't fully explain the practical implications of the magnitude of increase observed in the study. Is the observed increase in lactulose absorption clinically meaningful? Does it suggest a level of gut barrier dysfunction that is likely to have adverse health consequences?
Implementation: Add a sentence or two to explicitly address the clinical significance of the observed increase in intestinal permeability. Consider: (1) Comparing the magnitude of the increase to values seen in other conditions associated with gut barrier dysfunction (e.g., inflammatory bowel disease, type 1 diabetes). (2) Discussing whether the observed increase is likely to be associated with adverse health outcomes, based on existing literature. (3) Acknowledging any uncertainty about the clinical significance of the observed change.
This is a low-impact improvement that would improve the clarity and flow of the Discussion section. The Discussion section should avoid overly definitive statements about causality, given the limitations of the study design. The current wording in some places is too strong, suggesting a causal relationship between carrageenan and insulin resistance that is not fully supported by the data.
Implementation: Review the Discussion section and soften any language that implies a definitive causal relationship. Use phrases like "may contribute to," "suggests a potential role," or "is associated with" instead of "causes" or "leads to." For example, change "The data indicate that carrageenan acts in synergism..." to "The data suggest that carrageenan may act in synergism...".