Advanced cancer often results in reduced dietary intake; however, data on actual intake at the time of diagnosis are limited. In the present study, a detailed dietary intake assessment was performed in patients with metastatic lung and upper gastrointestinal cancer, before initiation of systemic therapy. Basic demographics and performance status (PS) were recorded. Nutritional status was evaluated through anthropometry, Mini Nutritional Assessment (MNA), and 3 nonconsecutive 24-hour dietary recalls. Of the 84 patients enrolled, 61.4% were protein, energy, or protein-energy undernourished, regardless of body mass index (BMI) or MNA category. No differences in energy, macronutrients, and micronutrients intakes across BMI categories were recorded. Very low consumption of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), irrespective of energy intake, tumor site, BMI category, or PS was found. Suboptimal micronutrients intakes were recorded even in well-nourished and overweight/obese patients. Patients with adequate PS and better MNA score reported significantly higher intake of certain macro- and micronutrients (all P < 0.05). Most patients exhibited reduced dietary intake in terms of energy, macronutrient, and micronutrient. Very low EPA and DHA intake was recorded for the whole sample, whereas micronutrient suboptimal intakes were also prevalent in well-nourished or overweight patients. All the above should be taken into account during patients' nutritional care.