Malnutrition is a common and significant concern among patients undergoing chemotherapy for solid tumors, particularly breast and lung cancer, and can adversely affect treatment tolerance, functional capacity, and quality of life. Regular assessment of nutritional status, including body weight, body mass index (BMI), and dietary intake, is essential for early identification and management of nutritional deficiencies. This study aims to explore and inform appropriate nutritional intervention strategies to improve the nutritional status, functional capacity, and quality of life of patients with solid tumors receiving chemotherapy. The primary objective of this study is to compare the effects of an oral nutritional protein supplement administered along with dietary counselling versus dietary counselling alone on protein intake. Secondary objectives include comparison of energy intake, total calorie intake, serum total protein levels, serum albumin to globulin (A/G) ratio, changes in body weight and BMI, hand grip strength assessed using a dynamometer, quality of life, and treatment-related toxicities. Energy and protein intake will be assessed at baseline and at weeks 4, 8, and 12 using a food diary provided by the study team. Blood samples collected at baseline and at the end of the study will be used to assess biochemical nutritional parameters, including serum protein and albumin–globulin ratio. Quality of life will be evaluated at baseline and during follow-up visits using validated questionnaires. Compliance will be assessed based on the proportion of the prescribed nutritional supplement consumed. Safety will be monitored at baseline and at each study visit until the end of the study through clinical assessments and documentation of adverse events.