Sarcopenia-the progressive loss of muscle mass and strength-is a major clinical issue, especially in surgical patients with malignancy. It's strongly linked to poor postoperative outcomes like increased complications, longer hospital stays, and higher mortality. Surgical stress (trauma, fasting, immobilization) significantly worsens this muscle catabolism.

Consequently, early identification and targeted preoperative intervention are essential. Preoperative nutrition, part of a prehabilitation program, is a key strategy known to attenuate muscle loss and improve recovery. The Skeletal Muscle Index (SMI) is an objective metric used for risk stratification.

The Siriraj Integrated Preoperative and Prehabilitation Center (SiPAP) uses a multidisciplinary model with nutritional counseling, but lacks routine sarcopenia screening or objective SMI measurement. Therefore, the impact of their specific nutritional interventions on preserving muscle mass remains unevaluated.

Hypothesis: The structured, individualized preoperative nutritional intervention delivered by SiPAP to intraabdominal oncology patients will result in a net preservation or positive change in the Skeletal Muscle Index (SMI) over the preoperative period.

Sarcopenia, defined as the progressive loss of skeletal muscle mass and strength, is clinically associated with poor clinical outcomes, increased physical disability, and low quality of life.1 Sarcopenia is common in a geriatric population, but it is also frequently observed in patients with cancer and other chronic conditions..

In patients undergoing surgery, especially those with malignancy, sarcopenia is independently associated with poor postoperative outcomes. It leads to frailty, delayed functional recovery, increased complication rates, prolonged hospital stays, and higher mortality.2-9 For cancer patients, a progressive decrease in muscle mass is a common issue, even during treatment such as neoadjuvant chemotherapy.10-12 This catabolic state is clinically relevant even over short time frames. A reduction of ≥10% in skeletal muscle index is considered clinically meaningful, and even modest short-term losses of 5-10% muscle mass in surgical or oncology patients are associated with poorer clinical outcomes and delayed recovery. 4,6,13-15 The pathophysiology of sarcopenia is multifactorial, involving reduced protein intake, physical inactivity, systemic inflammation, and hormonal changes. Surgical stress exacerbates muscle catabolism through mechanisms such as surgical trauma, perioperative fasting, and postoperative immobilization. 3-6,8,16-19 These effects are particularly concerning in older patients undergoing major procedures.3-6,8,16-19 Consequently, early identification and targeted intervention to preserve muscle integrity are essential of perioperative care for improving postoperative recovery and surgical outcomes. Body composition assessment, particularly using the skeletal muscle index (SMI), is an important metric in preoperative risk stratification and may help identify patients most likely benefit from prehabilitation.

Preoperative nutritional interventions, delivered as part of structured prehabilitation program, represent a key strategy to counteract perioperative muscle wasting. These interventions programs typically involve individualized nutrition counseling, targeted protein supplementation, and physical activity guidance. 20-28 Several studies have demonstrated the beneficial effects of optimizing nutrition to prevent and manage sarcopenia. Tailored dietary advice, with particularly focus on adequate protein intake, has been shown to attenuate muscle mass loss and improve muscle strength in patients at- risk patients of or diagnosed with sarcopenia. 22,24,26,27 In older surgical patients, individualized nutrition interventions are associated with improvements in physical performance measures such as gait speed, and handgrip strength, and short physical performance.27 Furthermore, nutritional guidance, when combined with exercise therapy as part of multimodal prehabilitation, has been reported to enhance muscle protein synthesis, support functional recovery, and reduce sarcopenia progression both before and after surgery. 24,28 These findings highlight the critical role of structured nutritional counseling in preserving skeletal muscle integrity during the perioperative period, aligning with the principles of Enhanced Recovery After Surgery (ERAS) protocols aimed to optimize patients' physical status and accelerating recovery.29-32 The Siriraj Integrated Preoperative and Prehabilitation Center (SiPAP) implements a multidisciplinary prehabilitation model, including comprehensive nutritional counseling and nutritional status assessments, aligned with ERAS principles. However, SiPAP has never formally screened for sarcopenia, nor has it routinely used objective measures of muscle mass, such as Skeletal Muscle Index (SMI) calculated from Bioelectrical Impedance Analysis (BIA). Given the strong association between sarcopenia and poor surgical outcomes, this represents a significant gap in our current risk stratification. Therefore, the impact of the specific, structured preoperative nutritional interventions provided by SiPAP on objective muscle mass preservation (SMI) and the incidence of sarcopenia has not been evaluated in this population.

Therefore, investigators hypothesizes that is that the structured, individualized preoperative nutritional intervention in intraabdominal oncology patients will result in a net preservation or positive change in in skeletal muscle index over the pre-operative period (between the initial SiPAP consultation and hospital admission for elective surgery.

This prospective study aims to determine the absolute mean change in skeletal muscle index (SMI), which will be measured using bioelectrical impedance analysis (BIA) for the first time in this participants cohort, following the nutritional intervention period. Secondary objectives include

1. To quantify the absolute change in body weight (kg) and total calorie and protein intake (kcal/day, g/day) at hospital admission preoperatively.
2. To assess the improvement in nutritional status, defined by a change in PG-SGA, comparing baseline to pre-admission.
3. To establish the baseline prevalence and the change in sarcopenia classification based on AWGS criteria.

Inclusion Criteria:

1. Patients aged 60 years to 90 years
2. Schedules for elective major surgery and formally enrollment in the Enhanced Recovery After Surgery (ERAS) program at Siriraj Hospital. (At Siriraj Hospital, patients scheduled for pre-specific elective major surgeries are enrolled into the ERAS program as individual hospital protocols for each ERAS module. All patients are informed about the ERAS program by their surgical team.)
3. Referred to the SiPAP center for prehabilitation based on established ERAS hospital preoperative protocol.
4. Able to provide written informed consent and willing to undergo all research assessments at both time points.

Exclusion Criteria:

1. Presence of conditions that interfere with bioelectrical impedance analysis (BIA), including an implanted pacemaker or other non-removable electronic medical devices.
2. Use of medications or supplements known to acutely or chronically affect muscle mass (e.g. corticosteroids, hormonal therapies) during the study period.
3. Diagnosed neuromuscular disorders that affect baseline muscle mass and strength
4. Undergo emergency surgery
5. A planned interval of less than 14 days between the initial SiPAP visit and hospital admission for surgery.
6. Alcohol consumption or strenuous exercise within the 12 hours preceding the scheduled BIA measurement.
7. Incomplete data on muscle mass or nutritional assessment at either time point.

The patients who enroll to Enchanced Recovery After Surgery (ERAS) program, Siriraj Hospital and referred to the SiPAP program