Two patients are on your schedule Monday morning.
Margaret is a 62-year-old female with follicular thyroid cancer (FTC) who is scheduled for a total thyroidectomy. Her BMI is 28, appetite is stable, and the Malnutrition Screening Tool score is 0.
Carlos is a 64-year-old male referred for a resectable adenocarcinoma of the pancreatic head. He reports 15 pounds of unintentional weight loss over three months, early satiety, intermittent nausea, and epigastric pain after eating. His albumin is 2.8 g/dL, and his Malnutrition Screening Tool (MST) score is 4. He is scheduled for pancreaticoduodenectomy following neoadjuvant chemotherapy.
Both will undergo general anesthesia and major surgery. Their preoperative nutritional needs could not be more different, and that divergence is driven overwhelmingly by tumor type.
Malnutrition risk varies substantially by cancer site. In a large United States ambulatory oncology cohort, high MST scores, defined as MST ≥2 and indicating high malnutrition risk, were present in 10% of breast cancers and 58% of upper gastrointestinal cancers.1 A separate French multicenter prevalence survey found malnutrition in 66.7% of pancreatic cancer patients.2 These measurements are not equivalent, but together they underscore the clinical evidence that the tumor’s location largely determines how much nutritional damage has already occurred even before the surgery is considered. Transcriptomic analysis across 12 tumor types confirms a molecular basis for this gradient: pancreatic adenocarcinoma showed the highest number of upregulated cachexia-inducing factor genes among the tumor types analyzed, with 14 of the 25 CIF genes upregulated compared with matched normal tissue, while breast and prostate cancers were among the types least associated with cachexia.3 Cachexia can still develop in metastatic breast cancer through circulating mediators including GDF15 and Activin A. Nutritional risk is associated with a 2.27-fold higher adjusted odds of postoperative complications and worse overall survival (hazard ratio 1.66). In a global study of more than 5,700 gastrointestinal cancer surgery patients, severe malnutrition was estimated to mediate 32% of early postoperative deaths in low- and lower-middle-income countries and 40% in upper-middle-income countries.4,5
Tumor biology is accessible before surgery. Using it to guide nutritional preparation is a good way to ensure patients receive the highest-quality, most specific nutritional preparation possible before induction.
ERAS Protocols: An Excellent Starting Point, but there is more.
Enhanced Recovery After Surgery (ERAS) protocols have improved outcomes through preoperative carbohydrate loading, protein targets, and shorter fasting windows.
The rationale for carbohydrate loading is metabolic: shifting the patient from a fasted to a fed state blunts the cortisol- and catecholamine-driven insulin resistance induced by surgery, with meta-analyses confirming shorter length of stay and faster gastrointestinal recovery.6,7 ERAS was developed and validated in general surgical populations. When applied to oncology patients without modification, it misses several tumor-specific metabolic vulnerabilities including the Warburg Effect. Understanding those vulnerabilities and integrating them into the patient’s pre-surgery nutrition plan can positively affect their outcomes.
The Warburg Effect: these tumors prefer glucose; should clinicians care?
Often aggressive tumors preferentially convert glucose to lactate even when oxygen is available, a pattern known as the Warburg effect. This raises a clinically important question because aerobic glycolysis supports rapid biosynthesis, immune evasion, and invasion: does providing a high-glycemic carbohydrate drink before surgery inadvertently fuel a glycolytic tumor during a period of already elevated metabolic demand?8,9
The Warburg effect is not uniform across cancer types, and the premise that sugar feeds cancer needs to be qualified, especially when preparing these patients for surgery.
Warburg Effect: Tumor Type at a Glance
Higher Glycolytic Activity
- Aggressive lymphomas (DLBCL, Hodgkin, Burkitt)
- Head and neck squamous cell carcinoma
- Non-small cell lung cancer, especially squamous histology
- Triple-negative breast cancer
- Colorectal adenocarcinoma
- Esophageal cancer
- Melanoma
- Cervical squamous cell carcinoma
- Glioblastoma
- Pancreatic ductal adenocarcinoma
Lower Glycolytic Activity
- Well-differentiated prostate adenocarcinoma
- Well-differentiated neuroendocrine tumors
- Mucinous colorectal, signet-ring gastric, and some ovarian cancers*
- Well-differentiated thyroid cancer
- Low-grade gliomas
Glycolytic activity varies by grade, stage, and tumor biology. This reflects general patterns, not absolute categories. *Some mucinous subtypes show variable FDG avidity.
The most direct clinical signal in the surgical context comes from a 2019 Norwegian randomized controlled trial by Lende et al. in ER-positive breast cancer patients, in whom preoperative carbohydrate loading was associated with increased tumor proliferation markers and worse relapse-free survival in T2 tumors. However, the hazard ratio carried very wide confidence intervals (HR 9.3, 95% CI 1.1 to 77.7), reflecting the small sample size.10 A single trial cannot settle the question for all cancers, but it makes a point worth noting. The composition of preoperative nutritional prep is a biologically active decision with measurable outcomes.
The American Society of Clinical Oncology’s (ASCO) 2022 guidelines state that there is currently insufficient evidence to recommend carbohydrate-restricted or ketogenic diets during cancer treatment.11 That position sits alongside, rather than dismissing, the growing mechanistic and early clinical evidence that carbohydrate source and glycemic impact matter in this population.
Glycemic Stability: What Every Surgical Oncology Patient Shares
Regardless of tumor type, perioperative hyperglycemia is an independent risk factor for surgical site infection, impaired wound healing, and postoperative complications in both diabetic and non-diabetic patients. Hyperglycemia impairs leukocyte function, including neutrophil chemotaxis, phagocytosis, and bactericidal activity; disrupts collagen synthesis; and compromises microvascular perfusion at the wound site.12,13,14
Preoperative carbohydrate support that avoids a sharp glucose spike is a better perioperative preparation option than standard drink recommendations, which often use maltodextrin or table sugar as the primary carbohydrate source. Both carry a high glycemic load; therefore, they potentially drive perioperative glucose levels higher. Lower-glycemic options are not yet widely standardized, reflecting a genuine gap between metabolic science and current clinical practice. For patients with high-Warburg tumors, there is additional tumor-specific rationale, but the glycemic stability argument stands independently across all oncology surgery patients. Clinicians whose practice does not extend into this territory should refer to a cancer-literate nutritionist or practitioner with oncology nutrition training.
The Pancreatic Cancer Case: When Digestion is Already Compromised
Back to Carlos. Exocrine pancreatic insufficiency can affect 50 to 92% of patients with unresectable pancreatic ductal adenocarcinoma and up to 80% or higher following surgical resection. Some studies report rates of 68 to 87% after pancreaticoduodenectomy specifically. 15,16 Ductal obstruction prevents secretion of all three major classes of digestive enzymes, resulting in simultaneous maldigestion of fat, complex carbohydrates, and protein. A study by Ladas et al. reported that patients with exocrine pancreatic insufficiency caused by chronic pancreatitis or pancreatic cancer malabsorbed approximately 10% to 30% of ingested complex carbohydrate, compared with about 1% on average in healthy controls. 17 This matters directly for preoperative carbohydrate loading: maltodextrin requires pancreatic amylase for initial hydrolysis. This step is impaired or absent in this population.
Different carbohydrate sources carry varying digestive burdens. Carbohydrate digestion is partially preserved through brush-border disaccharidases, specifically maltase, sucrase, and lactase, all of which are enterocyte enzymes not dependent on pancreatic secretion. Clinicians working with patients undergoing pancreatic or upper gastrointestinal surgery can raise carbohydrate intake as an impactful clinical variable. NCCN recommends PERT for pancreatic cancer patients with exocrine insufficiency symptoms, starting at ≥48,000 lipase units per meal, preferably 72,000.18 Despite this, one US study found that only 46.5% of patients with metastatic pancreatic cancer received it at subtherapeutic average doses.19 Identifying and addressing this gap is also an important contribution any clinician can bring to the surgical care team.
Immunonutrition: Evaluate What Is in the Package
Preoperative immunonutrition with arginine, omega-3 fatty acids, and RNA nucleotides has strong supporting evidence. A 2026 meta-analysis of 90 randomized controlled trials involving 7,462 patients found significant reductions in anastomotic leak (OR 0.62), respiratory infections (OR 0.46), wound infections (OR 0.67), and sepsis (OR 0.45). Hospital stays were shortened by a mean of 2.47 days.20 Notably, omega-3 fatty acids alone did not improve postoperative morbidity; the full combination is required. Five to seven days of preoperative immunonutrition is consistent with multiple international guidelines for malnourished patients undergoing major gastrointestinal or pancreatic surgery. However, many commercially available immunonutrition products contain substantial added sugar. Review carbohydrate composition carefully before recommending any specific product.
Hydration: A Useful Therapeutic Intervention
Cancer patients arrive for surgery with a dehydration burden that is rarely acknowledged. Chemotherapy toxicity, gastrointestinal losses, and reduced oral intake deplete volume well before the surgical fasting window begins.21,22 Preliminary national data suggest radiotherapy-related nausea, vomiting, and dehydration account for a proportion of unplanned oncology hospitalizations (conference abstract; not yet peer-reviewed).23 Additionally, hyponatremia, driven partly by volume depletion, occurs in 25 to 45% of lung cancer patients and is an independent predictor of poor outcomes.2
Adequate preoperative hydration directly reduces postoperative nausea and vomiting. The mechanistic pathways are detailed in the sidebar. Clinically, a retrospective study of 11,500 outpatient surgery patients found a 27% relative reduction in nausea when oral clear fluids were permitted up to surgery,29 and a JAMA Surgery quality-improvement study of over 76,000 patients found an association between a liberal fluid policy and reduced PONV from 10.6% to 9.4%.30 The 2023 ASA guidelines permit clear liquids up to 13.5 oz (400 mL) until two hours before elective procedures in appropriate candidates; cancer patients with diabetes, opioid use, or gastroparesis may fall outside this qualifier and should confirm with the anesthesia team.32 Plain water is appropriate for the morning fluid window. Adequate hydration before surgery applies to all elective and urgent surgical patients, whether or not they are oncology patients.
Nutrition Screening
Nutritional risk screening using the PG-SGA or NRS-2002 should begin at the time of diagnosis and be repeated before surgery. Pancreatic and upper GI cancers warrant immediate assessment; breast and genitourinary cancers warrant screening with escalation triggered by weight loss or advancing disease.
Protein optimization targeting 1.2-1.5 g/kg/day is appropriate across tumor types. Higher targets of up to 2.0 g/kg/day are supported in active prehabilitation programs that incorporate structured exercise.33,34
Preoperative carbohydrate support should favor lower-glycemic options where available. In pancreatic and upper GI cases, the carbohydrate source warrants explicit discussion with your patient and their surgical team.
While immunonutrition containing arginine, omega-3 fatty acids, and nucleotides for five to seven days preoperatively is supported by strong evidence in malnourished GI and pancreatic surgery patients, it is important to review the carbohydrate content of any commercial formulation.
Lab assessment should prioritize 25-OH vitamin D, zinc, iron studies, and B12. Take into consideration that serum zinc and magnesium are unreliable standalone indicators of tissue status. Clinical history and dietary patterns should inform repletion alongside lab values.
Both Patients Deserve Targeted Nutritional Support
Margaret will likely recover well. She still deserves more than a standard preoperative instruction sheet. Preparing her means she arrives at surgery protein-replete, well-hydrated, micronutrient-sufficient, and supported by a preoperative carbohydrate that optimizes glycemic stability, immune function, and wound repair.
Carlos needs all of that and considerably more, beginning weeks before his surgical date. His enzyme deficiency needs to be identified and addressed. His carbohydrate sources need to be reconsidered in light of what his pancreas can no longer do. His cachexia-driving tumor biology needs to inform every nutritional decision made on his behalf.
A clinician who screens their patients for nutritional status, applies tumor metabolism to preoperative nutritional needs, and counsels patients on adequate hydration before surgery sets their patient up for immediate, positive outcomes in oncologic surgery.
Thea Marx, ND, is a licensed naturopathic physician in private practice in Shelton, Connecticut, and the Founder/CEO of TM Nutrition LLC. Her clinical focus spans cellular nutrition, complex endocrine and hematologic conditions, and preoperative metabolic readiness. Dr. Marx completed her Doctorate in Naturopathic Medicine magna cum laude at the University of Bridgeport, with advanced training in nutrigenomics and precision nutrition under Dr. Peter D’Adamo. Her doctoral thesis addressed the development of post-cardiac surgical nutrition protocols, in which she mapped the surgical stress response and subsequent nutrient depletion. She has presented her perioperative nutrition research at national and international surgical and nutrition conferences. Disclosure: Dr. Marx is the developer of Vis Pre-Surgery, a perioperative medical food.
LinkedIn: linkedin.com/in/thea-marx/
SIDEBAR: Hydration Before Surgery: What Every Oncology Patient Should Know and Every Clinician Should Address
Why cancer patients arrive depleted
Severe chemotherapy-induced diarrhea can cause fluid losses of up to 4 to 6 liters per day. Despite the use of hydration protocols, Cisplatin-induced nephrotoxicity still occurs in nearly 20-30% of patients. This underscores how important fluid management is and should extend into the preoperative prep window. Preliminary national data suggest radiation therapy admissions for nausea, vomiting, and dehydration carry a mean hospital stay of approximately 4.6 days, with ICU-level care in approximately 12% of cases (conference abstract; not yet peer-reviewed). 23 Additionally, hyponatremia from volume depletion occurs in 25 to 45% of lung cancer patients and is an independent predictor of poor outcomes.Mechanism: how dehydration drives PONV
A 5% blood volume deficit reduces intestinal microcirculation by nearly 75% in experimental porcine models. Splanchnic hypoperfusion is proposed to stimulate serotonin release from enterochromaffin cells, activating the same 5-HT3 vagal pathway targeted by ondansetron. Hypovolemia also stimulates vasopressin release, and elevated vasopressin is independently associated with nausea in a self-amplifying cycle.Clinical evidence
In a retrospective analysis of 11,500 day-surgery patients, the incidence of nausea fell from 5.2% to 3.8% after a policy change permitting clear oral fluids up to the time of surgery. In a 76,000-patient JAMA Surgery quality-improvement study, antiemetic administration decreased by an estimated 14% (11.0% to 9.5%) under a liberal fluid policy, alongside improvements in patient-reported thirst. A 2026 randomized controlled trial found that early postoperative oral rehydration reduced the incidence of PONV by 21 percentage points in laparoscopic surgery patients.ASA guideline and eligibility
The 2023 ASA guidelines permit up to 13.5 ounces (400 mL) of clear liquids until 2 hours before elective procedures in appropriate candidates. Cancer patients with diabetes, gastroparesis, or opioid use may fall outside standard eligibility.What to recommend
Counsel patients to hydrate consistently in the days before surgery, not only the morning of the procedure. General targets: men, roughly 10-13 cups (2.5-3.0 L) of total fluids per day; women, roughly 8-9 cups (2.0-2.2 L) per day, per the Institute of Medicine’s Adequate Intake values. Plain water is appropriate for the morning fluid window if carbohydrate-containing beverages are not appropriate. Inform patients that pale yellow urine and regular voiding throughout the day are reasonable, evidence-supported indicators of adequate hydration.
