Globally, 842 milion people were unable to meet their dietary energy requirements in 2011-2013; the vast majority of them live in rural regions. Africa is the region with the highest prevalence of undernourishment (one in four people), with the North characterized by lower prevalence of undernourishment and much faster progress than the sub-Saharan region. Asia is really heterougeneous in respect to undernourishment: Western Asia presents the lowest prevalence, also South-Eastern and Eastern Asia present a low prevalence (around 10%) thanks to the rapid progress. 
According to the UN – FAO’s definition (World Food Summit, 1996), Food Security has four dimensions:
- AVAILABILITY of sufficient quantities of food of appropriate quality;
- ACCESS to adequate resources for acquiring food for a nutritious diet;
- ADEQUACY of food use to meet all physiological needs (clean water, sanitation and healthcare);
- STABILITY in time of the elements above.
All dimensions are fundamental to guarantee food security to the world population, however they intrinsically depend on a sufficient production of food and on the possibility to make it availabile to everyone, which are then the main pillars on which food security is based.
In order to meet the growing demand for food, the agricultural sector underwent different bursts of growth which, together with the economical evolution, enabled large expansions in the volume of food produced and in the availability of food to the population .
- INDUSTRIAL REVOLUTION (XIX century): farming machinery and food processing improvement increased the production and distribution of food;
- GREEN REVOLUTION (second half XX century): use of fertilizers, high-yield cultivars and irrigation techniques enhanced the agricultural production;
- TRADE INTENSIFICATION (XXI century): global trade allowed countries to rely on international food import, delocalizing food production and virtually using resources (in particular water resources) available abroad.
Recent evolution in food production and availability is thus linked to the international trade and the virtual water network and the concept of virtual water can be deployed for relevant and important consideration on the world food security.
 FAO, IFAD and WFP. 2013. The State of Food Insecurity in the World 2013. The multiple dimensions of food security. Rome, FAO.
 D'Odorico and Rulli. 2013. Nature Geoscience, 6, 417–418.