Simplification of human diets associated with increased accessibility of inexpensive agricultural commodities and erosion of agrobiodiversity leads to nutrient deficiencies and excess energy consumption. Non-communicable diseases are growing causes of death and disability worldwide. Successful food systems in transition effectively draw on locally-available foods, food variety and traditional food cultures. In practice this process involves empirical research, public policy, promotion and applied action in support of multi-sectoral, community-based strategies linking rural producers and urban consumers, subsistence and market economies, and traditional and modern food systems. Implementation of the International Plant Genetic Resources Institute's Global Nutrition Strategy in Sub-Saharan Africa offers a useful case study. Relevant policy platforms, in which biodiversity conservation and nutrition are and should be linked, include the Millennium Development Goals, Millennium Ecosystem Assessment, Convention on Biological Diversity, Global Strategy on Diet, Physical Activity and Health, Food-Based Dietary Guidelines, Right to Adequate Food and UN Human Rights Commission's Permanent Forum on Indigenous Issues. The largely unexplored health benefits of cultivated and wild plants include micronutrient intake and functions related to energy density, glycaemic control, oxidative stress and immuno-stimulation. Research on the properties of neglected and underutilized species and local varieties deserves higher priority. In tests of the hypothesis that biodiversity is essential for dietary diversity and health, quantitative indicators of dietary and biological diversity can be combined with nutrition and health outcomes at the population level. That traditional systems once lost are hard to recreate underlines the imperative for timely documentation, compilation and dissemination of eroding knowledge of biodiversity and the use of food culture for promoting positive behaviours.