Hunger is the drive to find and eat food. According to the World Health Organization (WHO), hunger is the world's major health risk. Globally, one in three people suffer from hunger, which is a result of a lack of food security. Food insecurity means people do not have access at all times to nutritionally adequate food. There are three dimensions to food insecurity: a lack of (1) purchasing power (lack of money or resources), (2) accessibility (ability to get food), and (3) availability (amount of food). In the United States, hunger is caused by poverty, whereas in developing countries it is caused by poverty, war, civil unrest, or an undeveloped economy.