Many cancer patients experience malnutrition, which can worsen their health and survival outcomes. However, limited research exists in our region on how common malnutrition is among hospitalized adults with solid tumors and what factors contribute to it. This study aimed to identify these factors and assess the effects of nutritional impact symptoms (NISs) caused by solid tumors on patients' nutritional status. Between July 2022 and February 2023, a cross-sectional study was carried out on the campuses of two major cancer treatment centers located in a national university hospital and a governmental hospital. Twelve NISs were adopted from the Patient-Generated Subjective Global Assessments (PG-SGA). The Nutrition Risk Screening 2002 (NRS-2002) instrument was used to thoroughly assess the risk of malnutrition. Multiple linear regressions were used to conduct a thorough study. A cohort of 294 participants was included. The prevalence of malnutrition risk (NRS score ≥ 3) was 26.9%. Parameters such as age, gender, marital status, educational level, monthly income, type of cancer and treatment modality, and the need for mealtime assistance exhibited statistically significant associations with malnutrition (p < 0.05). The results revealed a substantial inverse correlation between fluid intake and the NRS-2002 score (p < 0.001). Furthermore, symptoms related to solid tumors and their treatment, including chewing difficulties, fatigue, dry mouth, anorexia, constipation, nausea, dizziness, and a sensation of fullness, were also significantly associated with malnutrition (p < 0.05). Additional insights from the regression analysis underscored the independent correlation between the risk of malnutrition in solid malignant malignancies and factors such as anorexia (p < 0.001), colorectal cancer (p = 0.003), gender (p = 0.018), educational attainment (p = 0.049), and the need for mealtime assistance among patients (p < 0.001). Malnutrition is a major issue among adult cancer patients, particularly those with solid tumors. Anorexia, colorectal cancer, gender, educational attainment, and the need for mealtime assistance were identified as factors that led to malnutrition in our research. This study emphasizes the need for a multidisciplinary plan of care to diagnose and treat malnutrition, improve overall therapy, and reduce mortality and morbidity.