It is increasingly recognised that the food we eat has a significant impact on both human and planetary health.^{(Reference Laine, Huybrechts and Gunter1)} Encouraging the adoption of healthier and more sustainable food behaviours is a public health priority. Supermarkets are an integral part of the food environment which can influence food behaviour as they are the place in which most people purchase their food.^{(Reference Sacks, Schultz and Grigsby-Duffy2)} According to Nudge Theory consumer behaviour can be influenced by shaping the environment through a variety of mechanisms such as prominence and promotion in direct communications. Specifically, supermarkets are amongst the biggest spenders on marketing communications in Australia,^{(Reference Pash3)} and they regularly communicate with millions of Australians via a range of media channels and platforms. Despite the sizeable reach and potential influence of this activity, little is currently known about how supermarkets are using communications to influence food choices. The aim of this study was to explore the extent to which Australian supermarkets are supporting healthy and environmentally sustainable diet practices through their communications. A qualitative case study set in Sydney NSW, was used to monitor a sample of local and national communications from Australia's four largest supermarket chains over a three-month period from March to May 2022. Channels included in-store, social media, magazines, emails, websites and catalogues. A combination of deductive and inductive content analysis was used to evaluate these communications against a framework of 13 healthy and sustainable eating practices (HESDPs)^{(Reference Barbour, Woods and Brimblecombe4)} endorsed by Dietitians Australia. Evidence of Australian supermarkets both supporting and contradicting HESDPs was observed to varying extents. A key finding was the lack of explicit information about both the health and environmental sustainability impacts of food choices in messaging. Environmental sustainability was rarely mentioned and whilst nutritional benefits were occasionally communicated, more often than not, the healthiness of foods and recipes featured was either implied through visual cues or unclear. Benefits such as value, taste, freshness, ease and convenience were found to be more frequently communicated. The lack of clear communication about both the nutritional and environmental impacts of food choices, combined with communications which simultaneously support and contradict HESDPs, has the potential to confuse consumers who are increasingly looking to corporations to assist them in making healthier and more sustainable choices.