BackgroundMany cancer patients suffer from problems concerning nutrition and physical activity (PA) during and after their treatment. Forwarding reliable health information could help to alleviate severe symptoms. The present study aimed to examine cancer patients’ commonly used information sources on nutrition and PA.MethodsAn anonymous questionnaire was developed and distributed to German cancer patients in different settings. In total, 90 questionnaires have been completed between October 2021 and March 2022. For analysis, descriptive statistics were used and associations between information sources and patients’ lifestyle behaviour explored utilising Spearman’s Rho, Mann–WhitneyU, and Pearson’s Chi Square tests.ResultsThe cancer patients received information on nutrition and PA most frequently from physicians (70.9%), family and friends (68%) and browsing the internet (61.3%). Half of the patients (51.1%) had questions concerning these topics during the time of their disease. The majority of those patients (81.8%) reported that their questions were answered. The topics were addressed primarily with outpatient oncologists (60.0%) and in rehabilitation clinics (53.3%). Just about half of the patients (55.3%) felt satisfactorily informed on nutrition and PA in their cancer disease, more so if they talked to their oncologist or family physician (Z= − 2.450,p= 0.014 andZ= − 3.425,p= 0.001 resp.).ConclusionCancer patients receive information on nutrition and PA predominantly after their initial treatment. Since they might be missing significant information to alleviate severe symptoms during their treatment, the importance of nutrition and PA should be emphasised by clinicians early on in treatment.Trial registrationTrial Registration Number (May 7, 2021): 2021-2149-Bef.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00432-022-04282-w.