Food production and therefore human diet are identified as important sources of environmental impact. Unhealthy and unsustainable diets with high intake of meat and low intake of plant‐based products are predominant worldwide. On the other hand, a balance between health and sustainability is necessary, since diets that are environmentally sustainable could lack essential macro‐ and micronutrients and result in nutrient deficiencies, non‐communicable diseases and malnutrition. The aim of this project was to investigate the nutritional adequacy and environmental impact of adults' diet by comparing current dietary habits and new alternative dietary scenarios. First, a systematic review was conducted following PRISMA guidelines to assess the environmental impact of current diets and sustainable dietary scenarios such as vegan, vegetarian, pescatarian, omnivorous and optimised dietary patterns worldwide. In the second part of the project, an optimisation study was conducted, based on a multi‐objective optimisation approach, with the purpose of creating the optimal diet based on nutritional and environmental constraints for the adult Italian population. The dietary scenarios of the optimised models were developed in accordance with the Italian food‐based dietary guidelines. Food consumption data was extracted from the INHES study and used as baseline diet. A clear evaluation of the current environmental impact because of diet and potential sustainable dietary scenarios globally is challenging. Finally, national food‐based guidelines should be adjusted by suggesting healthy and sustainable dietary recommendations in line with traditional eating habits and local food availability in order the desirable dietary shifts towards sustainability to be feasible.