Eligibility criteria

Both observational studies and randomized controlled trials (RCTs) published in English were included, with no publication date restrictions. We used the following inclusion criteria: 1) population: adult patients with gastric, pancreatic, or colorectal cancer (any stage) before anticancer treatment; 2) intervention: dietary prehabilitation (any type, duration, and form), including nutritional supplementation but excluding other prehabilitation forms; 3) comparison: standard care (no intervention or placebo); 4) outcomes: nutritional status (assessed by any method), QoL (any method), and length of hospital stay (LOS; any method).

Exclusion criteria encompassed “grey literature,” such as conference materials, theses, government documents, brochures, newsletters, annual reports, blogs, podcasts, newspaper articles, case reports, and study protocols.

Information sources and search strategy

The search included Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Cochrane Central Register of Controlled Trials, Medline, and Google Scholar. Free‑text queries and built‑in thesauri (eg, MeSH in Medline, EmTree in Embase) were used. Initially, the searches had no time or language restrictions. However, only the papers in English were included in the final review. A follow‑up search was performed to incorporate the latest studies, ensuring a comprehensive review of nutritional prehabilitation impact on cancer patient outcomes.

A comprehensive search strategy was developed to identify relevant studies. Various combinations of keywords and Boolean operators were used to ensure a wide range of studies were captured (Supplementary material, Table S1).

This strategy aimed to capture the breadth of literature addressing dietary prehabilitation and its effects on outcomes, such as changes in nutritional status, LOS, and QoL in cancer patients. The search was conducted between August 20 and September 30, 2024. The review was updated on December 7, 2024.

Study selection process

Two reviewers (DG and MW) independently reviewed titles and abstracts of the relevant studies. For papers that appeared to meet the inclusion criteria, full‑text versions were assessed to determine eligibility for final inclusion in the systematic review. At each stage of the selection process, any differences between the reviewers were resolved through discussion and mutual agreement.

Study risk of bias assessment

The risk of bias was assessed using the Cochrane RoB2 tool for randomized trials, covering 5 domains: randomization, deviations from intended interventions, missing outcome data, outcome measurement, and selection of reported outcomes. The criteria were categorized as entailing “low,” “moderate,” or “high” risk of bias.¹⁷ For 1 non‑RCT study, the QUADAS‑2 tool was applied to evaluate patient selection, diagnostic tests conducted, reference standards, and study flow.¹⁸

Data collection process and data elements

Screening and data extraction were conducted by 2 independent reviewers (DG and MW) using Covidence software (www.covidence.org, Veritas Health Innovation Ltd., Melbourne, Australia). The extracted data included study details (authors, year, study design, follow‑up duration), population characteristics (sample size, country, cancer stage, malnutrition risk, sex, age, planned therapy, treatment duration), intervention characteristics (duration, dosing, type), and reported outcomes (weight, body mass index [BMI], nutritional status, muscle mass, grip strength, physical function, QoL, complications, C‑reactive protein [CRP] levels, LOS, readmission, and mortality).

Study selection

The study selection process, presented in the 2020 PRISMA flowchart (Figure 1), identified 462 records. After removing duplicates and evaluating 19 articles, 7 were excluded for not meeting the inclusion criteria (ie, population, intervention, or language). Ultimately, 12 studies, including 1 observational study and 11 RCTs, were analyzed. Studies involving multimodal prehabilitation, nonmalignant gastrointestinal diseases, or cancer recurrence were excluded.

Ethics

Due to the retrospective design of the study, no approval of an ethics committee and patient consent were necessary.

Characteristics of the included studies

In Tables 1, 2, 3 we summarize the nutritional interventions before oncological treatment, highlighting heterogeneity in cancer stages and profiles. Colorectal cancer patients dominated (6 studies), followed by gastric (4 studies) and pancreatic cancers (2 studies). Commonly assessed outcomes included LOS and general postoperative complications, for example, infectious, gastrointestinal, or postoperative wound–related, while muscle mass, grip strength, physical fitness, and QoL were less frequently evaluated.

Risk of bias

The risk of bias in the included RCTs was assessed using the Cochrane RoB2 tool (Supplementary material, Table S2). Some concerns were identified in most of the studies, with 3 rated as having a high risk of bias due to deviations from interventions, selective reporting, or outcome measurement issues. Overall, the studies were of high quality. One non‑RCT study was evaluated using the QUADAS‑2 tool, and the risk of bias was assessed as low.

Main findings

Effectiveness of dietary prehabilitation in gastric cancer

Patients with gastric cancer are particularly prone to malnutrition and cachexia due to tumor location, which hampers food intake and nutrient absorption.³⁶ Our review suggests that immunonutrition and ONS offer moderate benefits, especially for high‑risk, malnourished patients. Wang et al²⁰ reported that immunonutrition improved albumin and prealbumin levels while lowering inflammatory markers (interleukin‑6, tumor necrosis factor α), potentially reducing postoperative complications associated with inflammation. Although no significant reduction in complications was found, benefits may be more evident in higher‑risk groups.¹⁹ An interesting aspect seems to be the implementation of multimodal prehabilitation. A Lithuanian RCT³⁷ found that a multimodal prehabilitation program (including diet, psychological support, physiotherapy, smoking cessation) lowered complication risk by 60% within 90 days and improved QoL (RR, 0.4).

Difficulties related to food tolerance persist,³⁸ as some patients are unable to tolerate certain oral formulations.^21,39 In such cases, specialized enteral or parenteral nutrition may be more effective. Overall, immunonutrition and ONS can improve surgical outcomes in gastric cancer; however, standardized interventions and further research are needed to optimize composition of the formulations and individualize treatment based on nutritional status.

Effectiveness of dietary prehabilitation in pancreatic cancer

Pancreatic cancer is among the most aggressive gastrointestinal malignancies, often accompanied by advanced malnutrition at diagnosis.⁴⁰ While dietary prehabilitation, particularly immunonutrition, shows potential benefits, such as shorter LOS and improved nutritional status, data remain limited and inconsistent.^23,24 Gade et al²³ reported a 5‑day reduction in LOS with immunonutrition, though not significant due to a small sample size. De Luca et al¹⁴ highlighted slight reductions in postoperative infections and LOS with medical nutrition, stressing proactive support for severe malnutrition.

Bibby et al²⁴ observed modest preoperative weight gain with dietary support, yet 76.7% of patients lost at least 5% of body weight within a month postsurgery. A study by Christopher et al⁴¹ on the effect of exercise and nutritional interventions in patients with liver, pancreatic, and biliary tract cancer and a systematic review⁴² on multimodal prehabilitation in patients with pancreatic cancer showed that the combination of nutritional interventions and physical exercise improves postoperative outcomes and may prolong survival in pancreatic and related cancers. Future research should optimize formulations and delivery methods, including specialized enteral or parenteral regimens, to address cachexia and malabsorption in pancreatic cancer patients.⁴²

Effectiveness of dietary prehabilitation in colorectal cancer

Dietary prehabilitation, particularly with ONS and immunonutrition, benefits colorectal cancer patients who often face malnutrition and increased complication risks.^31,43 Burden et al^25,28 showed that preoperative ONS reduced the incidence of wound infections and weight loss in malnourished patients. A review on multimodal prehabilitation³ reported a 24.91‑meter increase in the 6MWD and fewer postoperative complications (RR, 0.27). Gillis et al⁴⁴ found that nutritional prehabilitation shortened LOS by 2 days, improved 6MWD, and lowered complication rates, though small sample size limited conclusions.

Immunonutrition, including arginine and ω-3 fatty acids, also shows promise. Lee et al³⁰ found it helped to maintain body weight postdischarge, though it did not significantly reduce overall infection rates. A meta‑analysis of 12 RCTs⁴⁵ investigating the use of immunonutrition to reduce the rate of postoperative infectious complications in patients with colorectal cancer showed a reduction in wound infections (44%) and systemic infections (56%), while enhancing the immune response of CD16+ and CD56+ cells. Ural et al⁴⁶ showed that supplements enriched with arginine, ω-3 fatty acids, and nucleotides improved weight, BMI, arm circumference, and reduced inflammation.

However, variations in interventions, doses, and durations make comparisons challenging. Standardized protocols and larger trials are essential to confirm long‑term benefits.

Prospects for new therapeutic strategies

Dietary prehabilitation shows potential for patients with gastrointestinal cancers, particularly pancreatic, gastric, and colorectal malignancies. Future approaches may focus on personalized interventions addressing nutritional deficits and metabolic status, guided by biomarkers and advanced screening tools.⁴⁷ Tailored diets enriched with amino acids (eg, arginine, glutamine) and multimodal programs combining nutrition, exercise, and psychological support demonstrate synergistic benefits.^3,8,10,13,14

Immunonutrition, incorporating ω-3 fatty acids, nucleotides, and probiotics, could reduce inflammation and improve gut health.^{9,14,19,20,23,40,45,46} For severe malabsorption or advanced disease, specialized enteral or parenteral nutrition may ensure adequate intake.^31,39,46 Nutrigenomics offers potential for precision interventions aligned with genetic and metabolic profiles.⁴⁸

Extending nutritional support beyond surgery could enhance recovery, prevent muscle wasting, and improve survival. Clinical trials are needed to validate and standardize these strategies for broader patient groups.

For internal medicine physicians, early identification of malnutrition in oncology patients is crucial. These patients should be referred to a clinical dietitian for the implementation of personalized dietary prehabilitation.

Strengths and limitations

This review encompasses diverse studies on gastric, pancreatic, and colorectal cancers, highlighting various nutritional interventions (eg, oral supplements, immunonutrition) and outcomes such as complications, nutritional status, muscle mass, QoL, and LOS. The inclusion of studies from multiple countries (Japan, China, Denmark, United Kingdom) enhances global applicability.

Due to substantial heterogeneity in the interventions, populations, and outcome measures, a meta‑analysis was not conducted. The findings are presented as a narrative systematic review, grouped by cancer type and clinical outcome indicators. It is also important to consider patient lifestyle factors, including alcohol consumption, as potential modifiers of the effectiveness of dietary prehabilitation. Alcohol may negatively impact nutritional status, metabolic functions, and immune response, which could ultimately limit the effectiveness of the intervention.

Heterogeneity in study populations, cancer stages, and intervention protocols limits the ability to draw definitive conclusions. Small sample sizes reduce statistical power, while the absence of blinding introduces potential bias particularly in subjective outcomes, such as QoL. Short follow‑up periods hinder evaluation of long‑term benefits, and the predominant focus on well‑nourished patients may obscure potential advantages for malnourished individuals. Additionally, inconsistent outcome measures further complicate cross‑study comparisons.

Conclusions

This systematic review suggests that dietary prehabilitation, particularly based on ONS and immunonutrition, may improve postoperative complications, recovery times, and nutritional status in patients with gastric, pancreatic, and colorectal cancers. Despite these promising indications, variability in study populations and methods, small sample sizes, lack of blinding, and brief follow‑up periods limit definitive conclusions. Larger, more rigorous trials with standardized outcomes are needed to establish the long‑term effectiveness of nutritional prehabilitation in oncology.