This is the first of two articles on the steepening challenges which confront global agriculture, food security and hence nutrition and population health. The recent deterioration in global food security has caught most experts by surprise. While the Asia Pacific region as a whole has so far fared reasonably well, there should be no complacency about medium to long term food security in the region, whether or not food security improves in the near future. The first paper places this debate in the context of the long-standing arguments between Malthusianists and optimists. The apparent reversal of position in the last decade of two leading agricultural experts is discussed. Their recent writings reflect intensified Malthusian concerns curbed in their writings from the 1990s. The paper concludes that far more credence needs to be given to the pessimistic position in order to avoid it becoming reality. The second paper focusses on five interrelated challenges to future food security in the Asia Pacific. These may be conceptualised as pathways by which pessimistic Malthusian scenarios become manifest. The mechanisms are (1) climate change, (2) water scarcity, (3) tropospheric ozone pollution, (4) impending scarcity of phosphorus and conventional oil and (5) the possible interaction between future population displacement, conflict and poor governance. The article concludes that a sustainable improvement in food security requires a radical transformation in society's approach to the environment, population growth, agricultural research and the distribution of rights, opportunities and entitlements.