OBJECTIVE: To examine the present methods used to define nutritional needs, and to analyse the intrinsic limitations of the reductionist chemical, biological and medical approaches to assess requirements. To establish the necessity to incorporate the complexities emerging from a broader understanding of the biological sciences as well as to include environmental and social dimensions in addressing nutritional needs. METHOD: Examples of the limitations of current approaches and the implications of these in defining potential solutions and policy options to address present nutritional problems are presented and discussed. CONCLUSION: The chemical and biological sciences have provided a strong base for nutrition and have been essential in establishing nutrition as a science with public health relevance. However, these approaches are clearly insufficient to address the main challenges that confront nutrition science now in the twenty-first century. There is a pressing need to include the social, economic and human rights aspects in order to define future policies that will secure the right to safe and nutritious food for all.