The negative health and environmental impacts of current food production and consumption patterns have intensified calls for a ‘food systems transformation.’ Transitioning toward plant-rich diets while lowering animal-sourced products is recognised as a key strategy for improving health and reducing environmental impacts, particularly in high-income countries. While some positive changes have occurred, a faster transition is needed to meet global health and environmental goals. Novel plant-based foods (NPBFs)—products made from plants or fungi designed to mimic and replace animal-sourced products (e.g. dairy, meat)—have emerged as convenient alternatives for meat and dairy and require minimal behavioural change. However, their health and environmental ePects are still not well understood. This thesis explored the role of NPBFs in environmentally sustainable and healthy dietary transitions through three studies. Study 1, a systematic review of 57 peer-reviewed and 36 grey literature sources (2016-2022) found NPBFs generally have lower environmental footprints than their animal-sourced counterparts, but their nutritional profiles are complex. The limited health evidence showed positive health outcomes when replacing animal-sourced products for plant-based meats. However, replacing dairy milk with plant-based drinks has shown mixed ePects on consumer health. While some evidence showed no changes in health outcomes when changing from dairy milk to plant-based drinks, other studies indicate that frequent substitution may lead to micronutrient deficiencies. Study 2, a mixed methods UK-based survey (n=423) revealed that motivations for dietary shifts towards plant-rich diets vary by socio-demographics group and type of diets (e.g. vegan, vegetarian, omnivorous). Those following plant-forward diets (e.g. vegan, vegetarian) often mention that their shifts were driven by environmental and/or animal welfare concerns, whilst those following flexible and omnivorous diets are more inclined to change their diet for health reasons. This suggests that health should be central to dietary interventions, but interventions need to be tailored to socio-demographic groups and their evolving individual behaviours. Study 3, a UK-based food basket analysis, demonstrated that partial substitutions of meat and dairy with NPBFs reduced environmental footprints, with minimal nutritional trade-offs. However, cost barriers remained for some NPBFs, particularly for plant-based meats and some plant-based drinks. These findings highlight the potential of carefully selected, nutrient rich, NPBFs to partially support dietary shifts. However, without policies ensuring nutritional standards, better categorisation, aPordability, and targeted interventions, their potential benefits remain an underutilised opportunity for widespread health and environmental gains.