This publication contains three in-depth studies on the cost of hunger. These studies: 1) review the theoretical background to and the empirical evidence of how nutrition intake affects economic growth; 2) investigate the relationship between dietary energy supply and economic growth; and 3) present a country case study on the cost of hunger in Sri Lanka in order to find the dual causality of increased protein intake and economic growth. From these three studies are drawn strong policy implications of how economic policy can enhance food security, thereby promoting pro-poor economic growth. For policymakers in developing countries and for international donors, an important conclusion of these studies is that all policies - including food aid - that enhance food security and reduce undernourishment promote economic growth, which positively affects the poor in developing countries. Policies to strengthen food security tend to focus on the humanitarian benefits; however, this publication maintains that such policies also promote pro-poor economic growth. This book sheds light on the relationship between food energy intakes and economic growth. Its results are intriguing not only for researchers but also for policy-makers and international donors.