With the food system estimated to be responsible for approximately one-third of greenhouse gas emissions(1) there is an urgent need to transition to healthy and more environmentally sustainable diets. Plant-based ‘milks’ are associated with lower greenhouse gas emissions than dairy milks(2) and many Australian consumers are making the substitution(3). The 2013 Australian Dietary Guidelines advise that plant-based ‘milks’ fortified with at least 100 mg of calcium per 100 ml (e.g., soy, rice or other cereal) can replace dairy milk in the diet(4). This study aimed to assess the likely population-wide nutritional implications of replacement of dairy milk with the main categories of plant ‘milks’ available in Australian supermarkets in November 2023. We used computer simulation modelling of data from the 2011–2 National Nutrition and Physical Activity Survey (n = 12,153 persons aged 2+ years)(5). Dairy milk (including from hot drinks) was replaced with each category of plant ‘milk’ and the likely impact on usual intake of key nutrients supplied by dairy milk was assessed across eight age groups (National Cancer Institute method). Mean usual protein intake was relatively unchanged when dairy milk was replaced by soy ‘milk’ but replacement by rice ‘milk’ led to reductions of 4–5% in older adults (71+ years), increasing the proportion of older men with an inadequate intake from 14% (95% margin of error 5.1) to 20% (8.1). Nine out of 11 categories of plant ‘milks’ were not fortified with riboflavin. Replacement of dairy milk with these products would likely reduce mean usual riboflavin intake by 11% in older adults, increasing the proportion with an inadequate usual intake from 20% (6.2, 5.8) to 30–31% (9.9, 6.3). Nine out of 11 plant milk categories were not fortified with vitamin B12, and replacement of dairy milk with these products would likely reduce usual intake by 10-49% depending on the population group, leading to the proportion of females aged at least 14 years with an inadequate usual intake of vitamin B12 to increase from between 5 (2.2) and 8% (4.0), depending on age, to between 11 (3.4) and 17% (5.4). All categories of plant milks were unfortified with iodine. As a result, replacement of dairy milk with plant ‘milks’ by females aged at least 14 years would likely reduce mean intake by 7–15% and increase the proportion with an inadequate intake from between 6 (4.2) and 12% (4.7), depending on age, to 15 (8.1) to 24% (6.0). In conclusion, replacement of dairy milk with most types of plant-based milk has the potential to adversely impact protein, riboflavin, vitamin B12 and iodine intakes by the Australian population. Advice about switching to plant-based milks needs to consider the population group concerned and a range of nutrients, not just calcium.