Cancer and its treatment place a strain on the patient's body. One of the first effects of the disease is weight loss, which is primarily associated with impaired nutrient supply and reduced food intake, which can result in nutritional deficiencies, leading to a poorer response to treatment and a deterioration in the patient's quality of life. For this reason, nutritional intervention is a very important measure, carried out in parallel with conventional treatment. The aim of this study is to compare nutritional knowledge among people diagnosed with cancer and the healthy population. The research tool was a questionnaire based on the KomPAN questionnaire, completed in paper form. The study was conducted between October 2023 and December 2024 on a group of 389 people. Nearly 90% of respondents believed that diet is an etiological factor in cancer, and 84% believed that diet can be a chemopreventive factor (more often among patients than healthy individuals, p<0.05). Almost all respondents (95.5%) believed that cancer patients should not consume highly processed foods containing additives (e.g. nitrates, nitrites, monosodium glutamate, hydrogenated fats, glucose-fructose syrup). Among the products not recommended for cancer patients, respondents indicated heavily salted products and dishes (87%), heavily baked products (82.5%), smoked products (80.5%), cured (78.5%), marinated (75%), repeatedly reheated (72%) and traditionally grilled in smoke (61.5%). On the other hand, among the dietary components beneficial for cancer patients, respondents indicated antioxidants (79.5%) and omega-3 fatty acids (71%), vitamins C and E (59%), bioactive substances, including coenzyme Q10, polyphenols, phytosterols (58%).