It calculates the DES for each area, an estimate of the average daily food energy available per person over a given period. But it isn't happening because it's access to food that's the real problem. This brief summary of the UN 1998 State of Food and Agriculture report provides you some basic information on the present-day food situation, as well as some of the future prospects. You can also read the brief press release describing the main findings of the report. To understand why people go hungry you must stop thinking about food as something farmers grow for others to eat, and begin thinking about it as something companies produce for other people to buy.
Food is a commodity.
Furthermore, agricultural producers choose to grow, not only what people will and can buy, but they grow things for which they will get the best price. This has various implications. For example, much of the best agricultural land in the world is used to grow commodities such as cotton, sisal, tea, tobacco, sugar cane, and cocoa, items which are non-food products or are maginally nutritious, but for which there is a large market. Millions of acres of potentially productive farmland is used to pasture cattle, an extremely inefficient use of land, water and energy, but one for which there is a market in wealthy countries. In other words, if you don't have the money to buy food, no one is going to grow it for you.