Complex, contradictory and confusing: exploring consumer dilemmas in navigating sustainable healthy nutrition knowledge.

Nations are revising dietary guidelines to include sustainability recommendations in response to climate change concerns. Given low adherence to current guidelines, consumer inertia is a challenge. A proliferation of nutrition information providers and dietary messages contributes to confusion. All this suggests that health professionals will face considerable obstacles in facilitating a population shift towards sustainable and healthy (SuHe) diets. This review explores the role of nutrition science in shaping dietary behaviour and the challenges of shifting the nutrition narrative to encompass both health and sustainability. Societal transformation towards the 'asks' of a SuHe diet will rely on consumer-level transformation of food acquisition, preparation, consumption, storage and disposal behaviours. Acceptance of a higher share of plant-based food and a reduction in animal protein in the diet is likely to provoke disorientations as consumers' previously unexamined beliefs are challenged. The challenges presented by portion size distortion, protein reduction and replacement, and the role of ultra-processed food are discussed here in terms of sources of confusion. The routes to change involve deeper understanding of responses to disorientations through processes of belief formation and transformation, which are the foundations of subjective knowledge and attitudes, likely mediated through affective factors. In tandem with introducing new potentially disorienting-to-consumers information, health professionals need to consider the environments where this information is presenting and consider how these environments are designed to support action. In doing so, reactance and backlash through belief rejection and behavioural non-adherence could be reduced.