Malnutrition is highly prevalent in patients with foregut tumors comprising head and neck (HNC) and esophageal (EC) cancers, negatively impacting outcomes. International evidence-based guidelines (EBGs) for nutrition care exist; however, translation of research evidence into practice commonly presents considerable challenges and consequently lags. This study aimed to describe and evaluate current international nutrition care practices compared with the best-available evidence for patients with foregut tumors who are at high risk of malnutrition. A multi-centre prospective cohort study enrolled 170 patients commencing treatment of curative intent for HNC (n = 119) or EC (n = 51) in 11 cancer care settings in North America, Europe and Australia between 2016 and 2018. Adherence criteria were derived from relevant EBG recommendations with pooled results for participating centres reported according to the Nutrition Care Model at either system or patient levels. Adherence to EBG recommendations was: good (≥80%) for performing baseline nutrition screening and assessment, perioperative nutrition assessment and nutrition prescription for energy and protein targets; moderate (≥60 to 80%) for utilizing validated screening and assessment tools and pre-radiotherapy dietitian consultation; and poor (60%) for initiating post-operative nutrition support within 24 h and also dietetic consultation weekly during radiotherapy and fortnightly for 6 weeks post-radiotherapy. In conclusion, gaps in evidence-based cancer nutrition care remain; however, this may be improved by filling known evidence gaps through high-quality research with a concurrent evolution of EBGs to also encompass practical implementation guidance. These should aim to support multidisciplinary cancer clinicians to close evidence–practice gaps throughout the patient care trajectory with clearly defined roles and responsibilities that also address patient-reported concerns.