Malnutrition occurs frequently in patients with cancer of the gastrointestinal (GI) or head and neck area and can lead to negative outcomes. The aim of this study is to determine the impact of early and intensive nutrition intervention (NI) on body weight, body composition, nutritional status, global quality of life (QoL) and physical function compared to usual practice in oncology outpatients receiving radiotherapy to the GI or head and neck area. Outpatients commencing at least 20 fractions of radiotherapy to the GI or head and neck area were randomised to receive intensive, individualised nutrition counselling by a dietitian using a standard protocol and oral supplements if required, or the usual practice of the centre (general advice and nutrition booklet). Outcome parameters were measured at baseline and 4, 8 and 12 weeks after commencing radiotherapy using valid and reliable tools. A total of 60 patients (51M : 9F; mean age 61.9±14.0 years) were randomised to receive either NI (n=29) or usual care (UC) (n=31). The NI group had statistically smaller deteriorations in weight (P<0.001), nutritional status (P=0.020) and global QoL (P=0.009) compared with those receiving UC. Clinically, but not statistically significant differences in fat-free mass were observed between the groups (P=0.195). Early and intensive NI appears beneficial in terms of minimising weight loss, deterioration in nutritional status, global QoL and physical function in oncology outpatients receiving radiotherapy to the GI or head and neck area. Weight maintenance in this population leads to beneficial outcomes and suggests that this, rather than weight gain, may be a more appropriate aim of NI.