**Background:** Lung cancer is the most commonly diagnosed malignancy in Poland, accounting for nearly 25% of all cancer deaths, with a 5-year survival rate of only 22–24% even in developed countries. Both the disease and its treatment (surgery, chemotherapy, radiotherapy) induce catabolism, systemic inflammation, and cachexia mediated by TNF-α, IL-1, IL-6, IFNα, IFNγ, LMF, and PMF. Nutritional deficiencies are especially common in advanced disease. The authors hypothesized that diet may support treatment outcomes, but evidence remains equivocal. This systematic review summarizes epidemiological evidence on associations between diet and lung cancer treatment effectiveness.
**Methods:** A literature search of EMBASE and PubMed was performed for papers published between 1977 and June 2022 using the terms "lung cancer" and "diet." The review followed PRISMA guidelines. Inclusion criteria were adult studies including RCTs, cohort, and observational studies. Of 863 papers initially identified (after deduplication), 20 studies were ultimately included after filtering for relevance and quality. Evidence was evaluated using Bradford Hill and CASP criteria. Due to data heterogeneity, findings were presented in narrative review format.
**Key Results:** Omega-3 PUFAs showed consistent benefits: Sánchez-Lara et al. (2014) found that NSCLC patients receiving EPA-supplemented oral nutrition gained 1.6 ± 5 kg of lean body mass versus a 2.0 ± 6 kg loss in controls (p = 0.01), with reduced appetite loss, fatigue, and neuropathy (p ≤ 0.05). Van der Meij et al. (2012) reported significantly higher QoL, global health status (B = 12.2, p = 0.04), physical and cognitive function (B = 11.6 and B = 20.7, p < 0.01), and social function (B = 22.1, p = 0.04) in the n-3 PUFA group. Finocchiaro et al. (2012) demonstrated significant reductions in CRP and IL-6 over 66 days in the intervention group. Murphy et al. (2011) found that fish oil (2.2 g EPA/day) maintained body weight (0.5 ± 1.0 kg gain vs. 2.3 ± 0.9 kg loss, p = 0.05) and muscle mass (69% maintained/gained vs. 29% in controls). A second Murphy trial (2011b) reported higher clinical benefit (60.0% vs. 25.8%, p = 0.008) and one-year survival (80.0% vs. 41.9%, p = 0.02) with fish oil supplementation. Vitamin C supplementation increased plasma levels by 99.8% (p < 0.05) in NSCLC patients (Tokarski et al.). Vitamin E (400 mg/day) reduced chemotherapy-induced peripheral neuropathy symptoms more effectively than acetyl-L-carnitine (p = 0.002) and glutamine (p < 0.001). The ketogenic diet (Zahra et al., 2017) showed poor oral compliance (mean actual use 16.9 of planned 42 days); median OS was 22 months for early discontinuers vs. 17.7 months for completers. Preoperative immunonutrition (Kaya et al., 2016) reduced postoperative albumin decline (14.69% vs. 25.71%, p < 0.001), complication rates (19.4% vs. 44.4%, p = 0.049), and chest tube duration (4 vs. 6 days, p = 0.019). Malnutrition and hypoalbuminemia were associated with greater chemotherapy toxicity (Arrieta et al., 2010): malnourished patients had higher overall toxicity (mean ranks 31 vs. 22, p = 0.02). Sun et al. (1999) found that selected vegetables improved median survival in stage III–IV NSCLC (15.5 vs. 4 months, p < 0.01).
**Clinical Implications:** The review supports early nutritional assessment and intervention at diagnosis to prevent cachexia, reduce treatment toxicity, and improve QoL. Omega-3 PUFAs, vitamin C, vitamin E, and immunonutrition show the strongest evidence for clinical benefit. However, data on survival improvement remain limited, and most studies had small sample sizes and heterogeneous designs. The authors emphasize that well-designed RCTs are needed before firm clinical recommendations can be made.