This randomised controlled trial examined older adults (≥65 years) with locally advanced gastric cancer undergoing neoadjuvant chemotherapy. Over 8 weeks, high-protein oral nutritional supplements (ONS) were compared to standard nutrition care. ONS improved calorie and protein intake and reduced malnutrition risk, though no significant differences were found in physical function or quality of life. Both groups experienced quality of life declines and increased fatigue during treatment. While ONS may help maintain nutritional status, further research is needed to assess long-term benefits.