Fundamentals of a healthy and sustainable diet.

Background: A healthy and sustainable diet is a prerequisite for population and planetary health. The evidence of associations between dietary patterns and health outcomes has now been synthesised to inform more than 100 national dietary guidelines. Yet, people select foods, not whole dietary patterns, even in the context of following specific diets such as a Mediterranean diet, presenting challenges to researchers, policymakers and practitioners wanting to translate dietary guideline recommendations into food-level selection guidance for citizens. Understanding the fundamentals that underpin healthy and sustainable diets provides a scientific basis for helping navigate these challenges. This paper's aim is to describe the fundamentals of a healthy and sustainable diet.

Results: The scientific rationale underpinning what is a healthy and sustainable diet is universal. Everyone shares a physiological need for energy and adequate amounts, types and combinations of nutrients. People source their energy and nutrient needs from foods that are themselves sourced from food systems. The physiological need and food systems' sustainability have been shaped through evolutionary and ecological processes, respectively. This physiological need can be met, and food systems' sustainability protected, by following three interlinked dietary principles: (i) Variety - to help achieve a nutritionally adequate diet and help protect the biodiversity of food systems. (ii) Balance - to help reduce risk of diet-related non-communicable diseases and excessive use of finite environmental resources and production of greenhouse gas emissions. (iii) Moderation - to help achieve a healthy body weight and avoid wasting finite environmental resources used in providing food surplus to nutritional requirements.

Conclusion: The fundamentals of a healthy and sustainable diet are grounded in evolutionary and ecological processes. They are represented by the dietary principles of variety, balance and moderation and can be applied to inform food-level selection guidance for citizens.