Cancer is the second leading cause of death globally, following microbial infection, with an estimated 16 million deaths projected by 2040. However, natural resources can potentially treat up to 60% of cancer cases. Various cancers, including those affecting the breast, prostate, stomach, colon, lung, liver, kidney, bone, skin, and blood, have strong dietary connections regarding their occurrence and prevention. Cancer and its treatments, particularly chemotherapy, are closely associated with malnutrition in humans. The adverse effects of medical therapies and the disease itself often prevent patients with cancer from meeting their nutritional needs through regular food intake. The etiology of malnutrition in patients with cancer is complex and multifactorial, influenced by the type and location of cancer, disease stage, side effects of treatment, economic status, functional capacity, symptoms impacting nutrition, fasting requirements, inadequate dietary therapy, and awareness of the clinical staff regarding the role of dietary habits in diagnosis, treatment, and quality of life. Although there have been advances in drug-targeted therapies, they remain unelucidated, and therefore, this review aims to elucidate the relationship between cancer, chemical treatments, and malnutrition. In addition, it highlights the significant role of medicinal plants in treating various cancers and mitigating the adverse side effects of chemotherapy, offering a comprehensive understanding of their nutritional, immunological, and therapeutic benefits.