Clinical, Functional, and Nutritional Efficacy of a Glutamine-Enriched Oligomeric Diet in Patients with Rectal Cancer

Abstract Aims This work aims to evaluate the efficacy of nutritional supplementation with a glutamine-enriched oligomeric diet (GEOD) compared to a standard polymeric diet (SPD) in terms of oncology treatment-related diarrhea (OTRD) (frequency and consistency of stools), gastrointestinal toxicity, and functional and nutritional progress. Methods This prospective cohort study compared two groups of patients with rectal cancer in treatment with neoadjuvant chemotherapy and radiotherapy who were at risk of malnutrition. Patients were randomized to receive either 400 ml of GEOD or of SPD from the start of radiotherapy to 30 days after its completion. Results Eighty patients were recruited, 40 per arm. The GEOD arm had improved stool consistency and a greater reduction in the number of stools compared to the SPD arm (p < 0.001). The relative risk (RR) of developing diarrhea in the GEOD arm was 0.059 (95% CI 0.015-0.229). There was a reduced risk of developing intestinal mucositis in the GEOD arm compared to the SPD arm [RR 0.202 (95% CI 0.102 − 0.399)]. The GEOD arm had greater improvements in functional and nutritional status (p < 0.001). Conclusions GEOD had a protective effect in terms of the development of gastrointestinal toxicity associated with chemotherapy and radiotherapy treatment in patients with rectal cancer.


Introduction
Major advances in the treatment of patients with cancer have been made in recent years.Despite this, toxicity related to radiotherapy or chemotherapy treatment or a combination of both remains high.Patients with cancer who undergo this type of therapy frequently present with symptoms that severely impair their clinical, functional, and nutritional progress.Specifically, it has been observed that pelvic radiotherapy is one of the main causes of nutritional deterioration, mainly due to radiation enteritis, which causes diarrhea, mucositis, and abdominal pain as well as, to a lesser extent, constipation (1).
Oncology treatment-related diarrhea (OTRD) is a side effect that causes deterioration in the patient's nutritional status, leads to frequent hospitalizations, and affects quality of life (2,3).For this reason, it is important to carry out early, precise nutritional interventions which guarantee that nutritional needs are adequately met, promote good nutritional status, and help control the diarrhea (4).The prevalence of OTRD may be as high as 74% of patients with cancer and depends on radiation doses and cancer treatment type; it is higher among female patients, those with a low BMI, older adults, and/or those who have had abdominal surgery (3).It is essential to detect OTRD early and implement the appropriate interventions in order to minimize progression to more serious states that could affect the continuity of cancer treatment and survival (5).
Patients with cancer are often at high risk of malnutrition due to the tumor itself, its location, and its extent; the oncological treatment received (surgery, radiotherapy, chemotherapy); the toxicity related to this treatment; the metabolic changes that occur (6); and the social environment surrounding the patient.Prior studies have demonstrated that malnutrition leads to a higher rate of hospital admissions, a longer length of hospital stay, lower quality of life, and greater mortality related to decreased tolerance to cancer treatments (7).Taking into account the negative effects of malnutrition in patients with cancer, it is essential to detect it early and indicate optimal nutritional support to minimize its progression.
In light of how highly prevalent OTRD and malnutrition are in patients with cancer, it is noteworthy that clinical practice guidelines recommendations focus on the pharmacological treatment of diarrhea, but do not specifically address the necessary nutritional support for patients (3,(8)(9)(10).A nutritional support plan can range from dietary advice to the use of commercial formulas, which include oral nutritional supplements (ONS), enteral nutrition via a feeding tube, or even parenteral nutrition (11), depending on the severity and persistence of the symptoms of OTRD and malnutrition.ONS may be the most common and efficacious tool to treat both symptoms, as long as there is adequate treatment adherence (12).
An oligomeric diet may be a nutritional therapy option for patients with OTRD due to its ease of absorption, suppression of proinflammatory cytokine production, and maintenance of mucosal integrity (13)(14)(15).However, there are no published studies specifically on the efficacy of intestinal peptide nutrition in patients with rectal cancer therapy-related diarrhea, although there are works on enteral glutamine supplementation that show positive results in improving the severity and symptoms of patients with radiation enteritis (16).Glutamine contributes to intestinal trophism, is the precursor of glutathione (a key molecule in the antioxidant chain), modulates the inflammatory response, protects cells from various insults by producing heat-shock proteins, and also influences apoptosis (17).During hypermetabolic situations, as abdominal and pelvic irradiation, a severe depletion of glutamine may occur due to high consumption, mediated in part by cortisol, which cannot be compensated by greater production, increasing its needs dramatically.Under these conditions, glutamine can become an essential amino acid, and its deficiency can compromise immune function, acid-base balance and enterocyte integrity (18,19).
The main studies available at present, which are on oligomeric formulas, have been conducted in patients with cancer undergoing chemotherapy and radiotherapy treatment, but focus on the oral mucosa, esophagus, stomach, or pancreas.They found varied results (20)(21)(22)(23)(24)(25)(26)(27).In this context, Sanz Paris et al.'s group published an algorithm on the nutritional management of OTRD with an oligomeric formula in 2019 (28).Based on this algorithm, Sanz Paris et al. published results on the clinical and nutritional efficacy of implementing this protocol in clinical practice, with very promising results (29).
This study aims to evaluate the efficacy of nutritional supplementation with a glutamine-enriched oligomeric diet (GEOD) compared to a standard polymeric diet (SPD) in OTRD (frequency and consistency of stools), gastrointestinal toxicity, and the functional and nutritional progress of patients with rectal cancer undergoing treatment with neoadjuvant chemotherapy and radiotherapy.This study describes-for the first time-results on the efficacy of an oligomeric enteral nutrition formula in terms of the clinical, functional, and nutritional improvement of patients with rectal cancer in antineoplastic treatment with chemotherapy and radiotherapy compared to a standard polymeric formula.

Study Design
This is a prospective cohort study, with two groups of patients with rectal cancer in treatment with neoadjuvant chemotherapy and radiotherapy and at risk of malnutrition, conducted from March 2021 to September 2022.

Study Population
Adult patients diagnosed with rectal cancer (confirmed by biopsy) in treatment with neoadjuvant chemotherapy and radiotherapy who had weight loss >5% in the last six months were recruited.Patients with diarrhea associated with antibiotic treatment; those who use H2-receptor antagonists, prokinetics, laxatives, or osmotic agents; those with Clostridium difficile infection; those with severe renal, heart, respiratory, or liver disease according to clinical criteria; pregnant or breastfeeding women; and those with an allergy or intolerance to any of the formula ingredients were excluded.

Sample Size Calculation
Regarding the sample size calculation, the results of the study by Sanz-París et al. (2021) (29) were used in which a mean difference in the number of stools/day of 2.75 and a standard deviation of 1.63 stools/day were obtained.With a confidence level of 95% and a power of 90%, we estimated a sample size of 27 patients per experimental group, foreseeing a 10% loss to follow-up, yielding a total of 54 patients.

Recorded Variables
Four visits were held: V1 -initial (15 to 20 days before starting radiotherapy), V2 -part-way through radiotherapy (15 sessions), V3 -end of radiotherapy (25 sessions), and V4 -follow-up at 30 days.Demographic (sex and age) and clinical data related to cancer diagnosis and antineoplastic treatment were collected.
The following assessments were carried out to determine the impact of nutritional supplementation: • OTRD: The number of stools per day as well as their consistency according to the Bristol Stool Scale (value from 1 to 7) were recorded in V1, V2, V3 and V4.• Intestinal toxicity: Using the National Cancer Institute's Common Terminology Criteria for Adverse Events version 5.0 (CTCAE 5.0), the presence of cancer treatment-associated gastrointestinal toxicity was evaluated: nausea, vomiting, abdominal pain, intestinal mucositis, diarrhea, and constipation.In addition, the following data were recorded: minimum, mean, and maximum radiation dose-volume for the irradiated intestine as well as the volume of the irradiated intestine (V40 < 150 cm 3 ).They were recorded in V1, V2, V3, and V4.

Nutritional Treatment
Following the ESPEN recommendations for cancer patients ( 6), all patients received dietary recommendations to increase energy and nutrient intake, and to control diarrhea (without insoluble fiber), through their usual diets.In addition, patients received two daily packs of the treatment under study or the control treatment (Supplementary material 1) on an ongoing basis from day 1 of radiotherapy until 30 days after its completion for a total of 12 wk.

Randomization
Randomization was performed using a number table by the person responsible for the study's statistical analysis.Each patient received a participant number that assigned him/her to a specific arm to receive one nutritional formula or another [Experimental (GEOD); Control (SPD)].Distribution between the arms followed a 1:1 ratio.

Ethical Aspects
The study was carried out in accordance with the Declaration of Helsinki.The study protocol, the patient information sheet, and the informed consent form were approved by the Drug Research Ethics Committee of the Principality of Asturias on 4/3/2021 with number 2021.067.All patients were informed of the conditions for participation in the study and agreed to participate after signing the informed consent form.

Statistical Analysis
The statistical study was carried out using the SPSS 22.0 program (IBM).The Kolmogorov-Smirnov test was used to assess whether quantitative variables followed a normal distribution, and these variables were expressed as mean and standard deviation.Student's t-test was used to compare quantitative variables.
Qualitative variables were expressed as absolute frequencies and percentages.The chi-square test was used to compare variables and the relative risk (RR) with a 95% confidence interval was calculated.
A p value less than 0.05 was considered significant.

Study Population
Eighty patients were recruited and evenly randomized into the treatment arm (40 subjects) or the control arm (40 subjects).None of the patients recruited were excluded and all completed the intervention and follow-up period.The demographic, initial anthropometric, and clinical parameters are shown in Supplementary material 2, with no differences found between the intervention arms.

Clinical Variables
There were statistically significant differences in the number of stools between groups in each visit, and within group, from V1 to V4, in the GEOD arm (p < 0.001), but not in the SPD arm (Figure 1).There were statistically significant differences in the consistency of the feces (Figure 2) starting in V2, with a more notable improvement in the GEOD arm.
There were no differences between arms in the prevalence of nausea, vomiting, and abdominal pain recorded in the visits, but there were differences in the presence of intestinal mucositis in V4 and the presence of diarrhea from V3; namely, these parameters improved in the GEOD arm (Table 3).The RR in the GEOD arm of developing intestinal mucositis in V4 was 0.202 (95% CI 0.102 − 0.399).The RR in the GEOD arm of developing diarrhea in V3 was 0.744 (95% CI 0.611 − 0.906) and in V4 it was 0.059 (95% CI 0.015 − 0.229) (Table 1).
A greater improvement in functional status was observed in the GEOD arm compared to the SPD arm (Table 2).
A greater improvement in nutritional status was observed in the GEOD arm compared to the SPD arm (Table 3).There were no differences between the arms in terms of weight, percentage of weight loss, or BMI upon assessment in the visits.It was observed that the difference in weight loss percentage between V1 and V4 was lower in the GEOD arm compared to the SPD arm [0.73% (3.87%) vs. 2.67% (4.58%)] (p = 0.001).
Greater improvements in prealbumin and CRP values were observed in the GEOD arm compared to the SPD arm (Table 4) starting at V3 and improvements in all values (including albumin) were observed in V4.
Adequate adherence to the prescribed treatment was observed, with high rates in terms of treatment compliance in both groups and during all visits, without differences between visits and groups (Figure 3).

Discussion
Cancer-related malnutrition and OTRD occur frequently in patients with rectal cancer.In this study, the comprehensive treatment of both clinical conditions with a glutamine-enriched oligomeric enteral nutrition formula restored nutritional status and reversed cancer treatment-associated digestive toxicity in a manner that was far superior to a polymeric diet.
The population recruited in both nutritional intervention arms was entirely homogeneous, and no differences were detected between the arms.In general, the patients recruited were older adults, mainly men, and had toxic habits such as alcohol or tobacco use, which were present in a high percentage in both arms.All had rectal cancer-mostly low and middle rectal cancer-in locally advanced stages and were able to receive neoadjuvant chemotherapy and radiotherapy treatment.All patients were at risk of malnutrition, both in terms of SGA and blood test variables, even though they had BMIs in the overweight range.
The GEOD was associated with a greater improvement in OTRD compared to the arm that received SPD.Specifically, a reduction in the number of stools and a greater consistency of the feces were detected beginning at the visit part-way through radiotherapy treatment (V2).A 2020 study by Sanz Paris et al. (29), which focused exclusively on the oligomeric diet, also noted a decrease in the number of stools and an improvement in stool consistency, as measured on the     In addition to improved OTRD, an improvement in intestinal mucositis was observed in the GEOD arm.This variable was not assessed in the 2020 study by Sanz Paris et al. (29) or in other studies, but it is clinically important in the patient's progress.One of the most striking results was the impact of the type of formula administered on nutritional status.Despite a similar energy and protein composition, the GEOD led to an improvement in nutritional status measured via SGA whereas this improvement was not as noticeable with the SPD.It could be explained because the GEOD formula contained omega-3.These types of fatty acids could have beneficial effects related to stabilize or improve appetite, food intake, lean body mass and body weight in patients with advanced cancer undergoing chemotherapy and at risk of weight loss or malnourished (6).Also, this may be explained if one takes into account that an easily digestible formula with hydrolyzed protein that is rich in medium chain triglycerides (MCT) and enriched with L-glutamine may be more effective in restoring nutritional status in patients with rectal cancer who are at risk of malnutrition, receive chemotherapy and radiotherapy treatment, and develop digestive toxicity.An improvement in nutritional status was observed in other studies carried out on elemental diets, but these studies had a control arm that did not receive any nutritional treatment.The study by Sanz Paris et al. (29) did not use a control arm and thus, the results obtained could only be compared in terms of the arm that received an oligomeric formula, but not in terms of efficacy compared to a polymeric formula.
Regarding the improvement in functional status, it was observed that a greater proportion of patients who received the GEOD reached an ECOG score of 1 at the end of follow-up compared to those who received the SPD.The study by Miranda Santos et al. (30) found that an improvement in nutritional status led to an improvement in functional status and quality of life measured by the ECOG scale.In that study, the researchers used a PG-SGA nutritional diagnostic tool very similar to the one used in this study.
At present, there are no scientific studies with similar objectives to those proposed in this work, which were aimed at describing how the symptoms associated with rectal cancer behave in relation to oral supplementation with an oligomeric diet compared to a polymeric formula.The authors have indeed found other studies in which elemental diets were used, specifically Elental®, an elemental fat-free diet rich in amino acids (25,27).The studies were conducted in the Asian population in patients diagnosed with squamous cell carcinoma, esophageal cancer, or rectal cancer.Unlike this work, the populations recruited in these studies were much smaller and the nutritional intake was lower (300 Kcal and 14.1 g/protein/day vs this study, in which patients received between 600 Kcal and 32 g/protein/day and 636 Kcal and 36 g/protein/ day).The follow-up period was also shorter and nutritional status was not evaluated via the SGA nor was it one of the main variables assessed.
The study that may be most similar to this one is the 2020 study by Sanz Paris et al. (29), which evaluated the efficiency of a nutritional protocol for the prevention of OTRD.The work analyzed an oligomeric diet and included different tumor locations.However, this study has several advantages over the work by Sanz Paris et al.: the follow-up period was longer (12 vs. 8 wk), it included a final follow-up visit after having completing radiotherapy, the sample was more homogeneous in terms of the tumor location (only rectal cancer vs various locations), the use of antidiarrheal drugs or agents was an exclusion factor-unlike the work by Sanz Paris et al. that did allow for the use of these drugs, which may have influenced the results-, there was not a large degree of variability in the supplementation regimen (400 Kcal and 18.6 g/protein/day and 600 Kcal and 27.9 g/protein/ day vs this study in which patients received between 600 Kcal and 32 g/protein/day and 636 Kcal and 36 g/ protein/day), and, most importantly, the efficacy of the oligomeric formula was assessed compared to a standard polymeric diet (25)(26)(27)29).
In regard to this study's limitations, it should be noted that the grade of gastrointestinal toxicity according to the CTCAE 5.0 scale was not recorded, but rather the absence or presence of the symptoms assessed (nausea, vomiting, abdominal pain, intestinal mucositis, and diarrhea).Recording these grades could have allowed for detected changes in symptom severity, which is of particular interest in diarrhea and intestinal mucositis.Dietary energy and protein intake was not assessed at baseline and during planned visits.Lastly, other limitations of the study are that it did not have a double-blind design, since it was not feasible to blind the nutritional supplements, and that it was only carried out in a single healthcare center.
In regard to this study's strengths, it should be noted that this is the first study to evaluate the efficacy of an oligomeric enteral nutrition formula compared to a standard polymeric formula in terms of clinical, functional, and nutritional improvement in patients with rectal cancer undergoing antineoplastic treatment with neoadjuvant chemotherapy and radiotherapy.It shows that specific nutritional support with an oligomeric formula goes beyond merely restoring the nutritional status of a patient with cancer, but rather it has an impact on the patient's clinical improvement, reducing digestive symptoms that affect his/her overall progress.This may be due to the use of partially hydrolyzed protein, the fact that fat intake was mainly in the form of MCT, the fact that glutamine-the main amino acid of the enterocyte-was supplemented, or other factors.
In conclusion, a glutamine-enriched oligomeric diet had a protective effect against the development of gastrointestinal toxicity associated with antineoplastic treatment, specifically in the development of OTRD and intestinal mucositis, and it contributed to the functional and nutritional recovery of patients with rectal cancer undergoing radiotherapy and chemotherapy treatment.

Table 3 .
evaluation of nutritional status in accordance with SGa.