The UK has committed to reduce greenhouse gas (GHG) emissions by 80 % relative to 1990 levels by 2050, and it has been suggested that this should include a 70 % reduction in emissions from food. Meeting this target is likely to require significant changes to diets, but the likely effect of these changes on population nutritional intakes is currently unknown. However, the current average UK diets for men and women do not conform to WHO dietary recommendations, and this presents an opportunity to improve the nutritional content of diets while also reducing the associated GHG emissions. The results of this study show that if, in the first instance, average diets among UK adults conformed to WHO recommendations, their associated GHG emissions would be reduced by 17 %. Further GHG emission reductions of around 40 % could be achieved by making realistic modifications to diets so that they contain fewer animal products and processed snacks and more fruit, vegetables and cereals. However, our models show that reducing emissions beyond 40 % through dietary changes alone will be unlikely without radically changing current consumption patterns and potentially reducing the nutritional quality of diets.