More than one billion people in the world are now undernourished, according to latest figures.The 2010 Global Hunger Index shows that child malnutrition is the biggest cause of hunger worldwide, accounting for almost half of those affected.Countries in sub-Saharan Africa and South Asia were shown to have the highest levels of hunger.The report's authors called on nations to tackle child malnutrition in order to reduce global hunger.The Global Hunger Index is produced by the International Food Policy Research Institute (IFPRI), Welthungerhilfe and Concern Worldwide.The UN Food and Agriculture Organization (FAO) defines hunger as the consumption of fewer than 1,800 kilocalories a day - the minimum required to live a healthy and productive life.Despite the number of undernourished people in the world falling between 1990 and 2006, the report's authors say in that number has crept up in recent years, with the data from 2009 showing more than one billion hungry people.