Little is known about who would benefit from internet-based personalised nutrition (PN) interventions. This study aimed to evaluate the characteristics of participants who achieved greatest improvements (i.e. benefit) in diet, adiposity and biomarkers following an internet-based PN intervention. Adults (n=1607) from seven European countries were recruited into a 6-month, randomized controlled trial (Food4Me) and randomized to receive conventional dietary advice (control) or PN advice. Information on dietary intake, adiposity, physical activity, blood biomarkers and participant characteristics was collected at baseline and month 6. Benefit from the intervention was defined as ≥5% change in the primary outcome (Healthy Eating Index) and secondary outcomes (waist circumference and BMI, physical activity, sedentary time and plasma concentrations of cholesterol, carotenoids and omega-3 index) at month 6. For our primary outcome, benefit from the intervention was greater in older participants and women. Benefit was greater for individuals reporting greater self-efficacy for “sticking to healthful foods” and who “felt weird if [they] didn’t eat healthily”. Participants benefited more if they reported wanting to improve their health and wellbeing. The characteristics of individuals benefiting did not differ by other demographic, health-related, anthropometric or genotypic characteristics. Findings were similar for secondary outcomes. Older individuals, women and individuals with less healthy diets at baseline benefitted more from PN advice. The odds of benefiting did not differ by weight status, genetic risk or socio-economic position. These findings have implications for the design of more effective future PN intervention studies and for tailored nutritional advice in public health and clinical settings.