In a wonderfully concise post, Raj Patel illuminates the way we count hungry people here in the US and around the world. While the idea of food security is one key data set here, the more stark picture is by counting calories.
So it's useful to have other ways of measuring the depth of hunger. Counting the number of calories that individuals get to eat every day is how the Food and Agriculture Organization of the United Nations (FAO) measures hunger in the world. They count how many people eat less than 1900 calories a day, and their index of hunger is 'undernourishment'. According to their most recent estimates, 1.02 billion people will be undernourished in 2009. Overwhelmingly these people were in poor countries (just over 15 million people were undernourished in rich countries from 2004 to 2006--if the global measure of hunger was "food insecurity," the number of hungry would be substantially higher).
The data used to calculate undernourishment helps to compass the depth of hunger, the degree to which people are going seriously without calories every day. By counting the average calorie intake of people who are already undernourished, you can get a sense of how badly off the hungry are. When their average intake is 300 calories below the minimum daily intake of 1900, they're considered intensely food deprived. The countries with deepest levels of hunger are Haiti, the Democratic Republic of Congo and Belize, where a hungry person has an average daily calorie intake of 430 calories below the minimum acceptable. [More]
Doing the math as you are inhaling Thanksgiving smells from the kitchen is a battle between your brain and your stomach, but suffice it to say 1900 calories is not much.
Hunger in the world is a sign of political failure and economic inefficiencies. It is also reflective of the need for labor and economic mobility and freer trade. These ideas currently are out of favor, so I expect the statistics for hunger, however calculated, to get worse in the foreseeable future.