Glutamine prevents diarrhea in colorectal cancer patients undergoing chemotherapy or chemoradiotherapy: a meta-analysis.

Introduction
Colorectal cancer is a major global health concern, affecting a significant number of individuals worldwide each year with considerable morbidity and mortality [1]. In recent years, there has been an observable increase in both the incidence and mortality of colon cancer on a year-on-year basis. It is currently regarded as one of the most common malignant tumours in the digestive system. It is anticipated that approximately 3.3 million new cases will emerge by 2040 [2]– [3]. Radiation therapy and chemotherapy represent key modalities for the treatment of this disease, with the objective of delaying the further development of the disease. However, this treatment can cause damage to the intestinal mucosal structure and increase intestinal permeability, as well as induce mitosis of intestinal crypt cells, increasing the ratio of intestinal crypt cells to intestinal villi cells [4]. This can result in a reduction in the effective absorption surface and the absorption rate of the intestine. The most typical clinical manifestation of these changes is diarrhoea [5]. The occurrence of diarrhoea will not only reduce the quality of life of patients, but also lead to poor nutritional status and decreased immune function of patients, and directly affect the tolerance and efficacy of patients. Therefore, it is of great significance to maintain intestinal function and reduce adverse reactions during treatment.
Glutamine is a non-essential amino acid in the human body, serving as an important energy source for fast-dividing cells such as intestinal cells. It plays a crucial role in maintaining the integrity of the intestinal mucosal barrier and in immune system function [6]– [7]. The results of animal studies [8]– [9] indicate that glutamine can mitigate the severity of colitis induced by chemoradiotherapy, alleviate intestinal mucosal damage, and improve the atrophy of intestinal epithelium and the destruction of the intestinal barrier in animals. This paper summarized previous studies [10–14], aiming to systematically evaluate the effect of glutamine on the prevention of chemoradiation-related diarrhea of colorectal cancer through meta-analysis.

Methods
This meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [15]. The pre-registration for our meta-analysis can be accessed via the International Platform Database for Registration Systems Evaluation and Meta-Analysis Protocols (reference number: INPLASY202490057). The full text is available for download from inplasy.com (https://inplasy.com/inplasy-2024-9-0057). It should be noted that ethical approval is not required for this study.

Search strategy
A comprehensive electronic search of articles published in the field was conducted by three researchers before 1 August 2024. A comprehensive manual search of the PubMed, Embase, Cochrane databases, CNKI and Wanfang was conducted in order to select relevant randomised controlled trials. For further details regarding the precise literature search strategies employed, please consult the Appendix (Supplementary Table S1).

Inclusion and exclusion
The document management process employs EndNote (X9) software, and two investigators undertake an independent assessment of the qualifications of the project. The initial stage of the process involves screening the title and abstract, after which the article in question is subjected to a comprehensive review. The studies included in this review were all randomized controlled trials. The following inclusion criteria were met: (1) Patients with colon or colorectal cancer; (2) Glutamine is used during chemotherapy or chemoradiotherapy. (3) Control groups were treated with blank control or placebo, and outcome measures included diarrhea. The following studies were excluded from this review: studies involving animals, and studies with insufficient data extraction, including abstracts, reviews, pharmacological reports, and other literature. Furthermore, any literature that is inconsistent with the content of this study will be excluded. Should the necessity arise to obtain pertinent research data, the authors will be duly contacted.

Bias & quality assessment
The two researchers conducted independent evaluations, preliminary selections and verifications of the Literature in accordance with a unified and standardized methodology. The Literature was included or excluded in accordance with the pre-established criteria, and the data were subsequently collected. The quality of the selected articles was evaluated in accordance with the Cochrane Reviewer Handbook 5.1.0 [16]. We used funnel plots(RevMan 5.4) and Egger’s test(Stata 15.0) to assess publication bias among the included studies.

Data synthesis and analysis
The meta-analysis was conducted utilizing RevMan 5.4 software. Data that met the pre-established criteria of homogeneity (P > 0.10 and I²≤50%) as determined by the heterogeneity test were analyzed using the fixed effects model (M-H). If uniformity (P ≤ 0.10 or I2 > 50%) was not met and heterogeneity cannot be excluded, a random effects model can be used to combine effects [17]. The estimates are expressed as relative risk(RR) or mean difference (MD) with a 95% confidence interval (CI). A p-value of less than 0.05 was deemed to be statistically significant.

Results
The flow chart (Fig. 1) provides an overview of the search and research selection process. A total of 260 articles were retrieved, of which 71 were excluded due to duplication. Furthermore, following an initial review of the title and abstract, 143 studies were excluded. A comprehensive evaluation was conducted on the remaining 46 studies, based on a full reading of the full text. Five RCTs evaluated the effect of glutamine on diarrhea undergoing chemotherapy or chemoradiotherapy in patients with colorectal cancer.
The principal characteristics of the included trials are set forth in Table 1. A total of 311 patients were included in the analyses. All of the included studies were randomized controlled trials. The estimates are expressed as relative risk(RR) or mean difference (MD) with a 95% confidence interval (CI). The results of meta-analysis showed that compared with the control group, the use of glutamine is linked to a reduced incidence of chemoradiation-induced diarrhea in colorectal cancer patients (RR = 0.72, 95%CI: 0.60–0.87, P < 0.01, I2 = 37%)(Fig. 2), and the level of D-xylose in the glutamine group was significantly higher than that in the control group (MD = 0.32, 95%CI: 0.14 ~ 0.51, P < 0.01, I2 = 0%)(Fig. 3), c-reactive protein was significantly lower than the control group (MD = 0.52, 95% CI: 0.72 ~ 0.32, P < 0.01, I2 = 0%)(Fig. 4).
To further explore the effects of glutamine on colorectal cancer under different administration routes (intravenous injection vs. oral administration), treatment strategies (chemotherapy alone vs. chemoradiotherapy), and populations in different regions (Western vs. Eastern populations), we conducted subgroup analyses (Supplementary Figure S1−3). The results showed no statistical differences in the analyses of administration routes and populations. However, glutamine had a more significant effect in reducing diarrhea in colorectal cancer patients receiving chemotherapy alone compared to chemoradiotherapy (RR = 0.65, 95%CI: 0.43–0.98, P < 0.05, I²= 35%). To explore potential differences by tumor site, we further conducted subgroup analyses based on primary tumor location, classifying the included studies into two subgroups: colorectal cancer and rectal cancer. As summarized in Table 1, the colorectal cancer subgroup-where patients generally undergo chemotherapy alone-showed a significant association between glutamine supplementation and reduced diarrhea incidence (RR = 0.65, 95% CI: 0.44–0.97, P < 0.05, heterogeneity, I²= 30%). By comparison, no statistically significant benefit of glutamine was observed in the rectal cancer subgroup (a population that typically receives chemoradiotherapy) (P > 0.05, Supplementary Figure S4). We conducted a separate analysis of English-published studies, and the results showed that the glutamine group had a lower incidence of diarrhea compared with the control group (RR = 0.80, 95%CI: 0.65–0.98, P < 0.05, I²= 27%) (Supplementary Figure S5).
The Revman software is employed to ascertain the influence of a single study on the overall pooled estimate of each predefined outcome. The results of the risk assessment of bias in these trials are presented in the Supplementary Figure S6. We evaluated publication bias using a funnel plot, and the results showed no evidence of publication bias, as depicted in Supplementary Figure S7, and conducting a formal evaluation using Egger’s test(Stata 15.0), which showed no significant publication bias(P > 0.05). The quality of the RCT experiments included in this study is high, which lends credibility to the conclusions of this study. This study assessed research certainty according to the criteria of the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) Guidelines Working Group [18]. According to the corresponding evaluation criteria, the evidence level was classified (divided into 4 categories: high, moderate, low and very low) [19]. Certainty of evidence for diarrhea, D-xylose and C-reactive protein was low (Supplement Figure S8).

Discussion
The objective of this meta-analysis was to evaluate the preventive value of glutamine for diarrhoea in patients with colorectal cancer undergoing chemotherapy or chemoradiotherapy. By synthesizing data from five high-quality randomized controlled trials (n = 311), our analysis revealed a significant 28% reduction in diarrhoea risk (RR = 0.72, 95%CI: 0.60–0.87) among patients receiving glutamine supplementation. Subgroup analyses further indicated differential efficacy based on treatment modality, with a more pronounced effect observed in chemotherapy cohorts (RR = 0.65, 95%CI: 0.43–0.98, P < 0.05). This divergence may reflect the distinct pathophysiological mechanisms underlying radiation versus chemotherapy-induced mucosal injury, with radiotherapy inducing more complex damage involving oxidative stress, crypt cell apoptosis, and chronic inflammation that may exceed the reparative capacity of glutamine at standard doses [20]– [21]. Comparison with prior meta-analyses highlights the specificity of our findings. While broader reviews of glutamine in cancer patients reported inconsistent effects on diarrhoea [22–24], our focus on colorectal cancer and chemoradiation regimens Likely reduces heterogeneity. For example, a 2020 meta-analysis including diverse cancer types found only marginal benefits of glutamine on gastrointestinal toxicity (RR = 0.88, 95%CI: 0.76–1.02), underscoring the importance of disease- and treatment-specific analyses [23]. Our subgroup results further emphasize the need to stratify by treatment modality and tumor location, as the differential efficacy between chemotherapy and chemoradiation groups, as well as between colorectal and rectal cancer subgroups, suggests distinct therapeutic thresholds for glutamine. Additionally, we conducted a separate analysis restricted to English-published studies, which consistently demonstrated a lower incidence of diarrhoea in the glutamine group (RR = 0.80, 95%CI: 0.65–0.98, P < 0.05, I²=27%). This finding, while limited by the smaller sample size of English-language literature in our dataset, supports the generalizability of glutamine’s efficacy across diverse study populations and methodological approaches.
Notably, subgroup analyses stratified by primary tumor location further refined these findings and uncovered critical therapeutic nuances: in the colorectal cancer subgroup-where patients were predominantly treated with chemotherapy alone (consistent with clinical practice for colon cancer, the primary component of this subgroup, Table 1)-glutamine supplementation was associated with a statistically significant reduction in diarrhea incidence (RR = 0.65, 95%CI: 0.44–0.97, P < 0.05). The low heterogeneity observed in this subgroup (I²=30%, P > 0.10) further supports the stability and reliability of this effect, indicating consistent benefit across included studies. By contrast, no statistically significant reduction in diarrhea risk was observed in the rectal cancer subgroup (P > 0.05, Supplementary Figure S4)—a population that uniformly received concurrent chemoradiotherapy (the standard neoadjuvant or definitive treatment for locally advanced rectal cancer). In clinical practice, colorectal cancer management predominantly relies on adjuvant chemotherapy regimens such as 5-fluorouracil/folinic acid (5-FU/FA) or oxaliplatin combined with capecitabine, which primarily induce intestinal mucosal damage through direct cytotoxic effects on rapidly dividing enterocytes [25]. In contrast, rectal cancer treatment typically involves neoadjuvant chemoradiotherapy or concurrent radiochemotherapy, where ionizing radiation exacerbates mucosal injury by triggering DNA damage, oxidative stress, and sustained inflammatory responses [21]. The synergistic toxicity of radiation and chemotherapy may introduce more severe and complex intestinal barrier disruption—including villous atrophy, crypt depletion, and increased permeability—that glutamine alone cannot fully mitigate, potentially explaining the null effect in the rectal cancer subgroup.
Mechanistically, chemoradiation disrupts intestinal homeostasis through multiple pathways. It inhibits thymidylate synthase in mucosal epithelial cells, impairs DNA synthesis, and triggers excessive nitric oxide production, leading to villous atrophy and increased permeability [26]. Concurrently, activation of NF-κB signaling upregulates pro-inflammatory cytokines (such as TNF-α, IL-6), further exacerbating mucosal damage and bacterial translocation [27]. Glutamine mitigates these effects by serving as a primary energy source for enterocytes, promoting the synthesis of heat shock proteins and antioxidants (such as glutathione), and enhancing tight junction protein expression (such as claudin-1) [28]. Our findings of improved D-xylose absorption (MD = 0.32, 95%CI: 0.14–0.51) and reduced CRP levels (MD = 0.52, 95%CI: 0.32–0.72) align with this mechanism, suggesting enhanced mucosal integrity and dampened systemic inflammation. However, the absence of standardized diarrhoea severity scoring across included studies limits direct correlation between biomarker improvements and clinical symptom relief. Specifically, definitions of diarrhoea in the included literature varied, with descriptions ranging from increased stool frequency to changes in stool consistency, lacking uniform criteria for grading severity. This heterogeneity hinders comparability between studies and complicates the interpretation of pooled results. Future research should adopt standardized assessment tools such as the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0, which defines grades of diarrhoea based on objective metrics (Grade 1: <4 additional stools per day vs. baseline; Grade 2: 4–6 additional stools per day) and explicitly excludes cases of infectious diarrhoea to ensure consistency [29].
This study has several limitations that warrant mention. First, the modest sample size (total n = 311 across 5 RCTs) and variable glutamine dosing (10–30 g/day oral to 0.3–0.5 g/kg intravenous) increased outcome heterogeneity, with low-certainty evidence (downgraded for imprecision and indirectness) highlighting the need for confirmatory trials. Second, inconsistencies in tumor location classification and reporting-including lack of distinction between colon/rectum sublocations, uneven sample distribution across subgroups, and unclear primary site in some studies-introduced confounding and reduced statistical power for subgroup interpretations, potentially contributing to false-negative findings in rectal cancer. Third, while publication bias appeared low, no eligible unpublished studies were found in ClinicalTrials.gov, warranting vigilance for “file-drawer” effects. Fourth, inconsistent diarrhoea definitions (no uniform use of tools Like CTCAE 5.0) limited conclusion robustness, and the absence of pharmacogenetic analyses (including genes regulating glutamine metabolism) prevented identification of responsive patient subgroups. Finally, though mechanistic biomarkers (elevated D-xylose, reduced CRP) align with efficacy, no included studies linked these changes to clinical outcomes like diarrhea severity or quality of life, leaving translational gaps; specifically, future research will require additional RCTs with clearer tumor classification and staging, alongside standardized reporting and validated endpoints, to fully address these limitations.

Conclusion
In conclusion, glutamine supplementation shows promise for preventing diarrhea in colorectal cancer patients undergoing chemotherapy or chemoradiotherapy, with more pronounced efficacy observed in those receiving chemotherapy alone and in the colorectal cancer subgroup. This potential benefit is likely linked to its roles in alleviating inflammation and supporting intestinal mucosal integrity—evidenced by elevated D-xylose levels (indicating improved absorption) and reduced C-reactive protein (reflecting dampened systemic inflammation). However, given the low certainty of current evidence, further high-quality studies are needed to validate these findings and clarify optimal dosing strategies.

Supplementary Information