BackgroundThis study assessed the impact of kilojoule (kJ) labelling alone or accompanied by a social marketing campaign on food sales and selection of less energy-dense meals by young adults from a university food outlet.MethodsThere were two kJ labelling intervention phases each of five weeks: (1) kJ labelling alone (2) kJ labels with marketing materials (“8700 kJ campaign”). Food sales of labelled items were tracked during each intervention and five weeks after. Food sales during interventions were also compared with historical sales of foods in the same 10-week period in the previous year. A sub sample of young adults (n = 713; aged 19–24) were surveyed during both the interventions to assess awareness, influence, sentiment and anticipated future impact of kJ labels and the social marketing campaign respectively.ResultsThere were no differences in sales between the kJ labelling with social marketing and the 5-weeks of labelling before and after. The percentage sale of chicken Caesar burger (3580 kJ, P = 0.01), steak and chips (4000 kJ, P = 0.02) and the grill burger (5500 kJ, P = 0.00) were lower in the year with menu labelling and social marketing campaign. Only 30 % students were initially aware of the kJ labels on the menu but 75 % of students were accepting of kJ labelling, after they were made aware. Respondents viewing the marketing campaign elements and then using kJ values on the menu selected meals with a lower mean energy content; constituting a reduction of 978 kJ (p < 0.01) even though the majority claimed that the 8700 kJ campaign would not impact their food choices.ConclusionsPoint-of-purchase energy labelling may be an effective method to encourage better food choices when eating out among young adults. However, further efforts to increase awareness and provide education about energy requirements to prevent weight gain will be needed.