And that's just in the US, says Timothy Jones, a professor at the University of Arizona.

A study by Jones and the U.S. Department of Agriculture in 2003 estimated that more than 50 million tons of edible food are wasted in the United States each year. The study looked at farming, retail establishments and homes. It found that:

• Twelve percent of American crops, valued at $20 billion, go unharvested due to difficulty in predicting demand.
• Retailers, including restaurants, throw away 35 million tons a year, valued at $30 billion.
• Households dump $43 billion worth of food a year, or about 14 percent of what they buy.
• American households throw away 1.28 pounds of food a day, 27 percent of which consists of vegetables.

Jones says that people often buy fresh vegetables because they think they are eating healthfully. But many then go home, pop a frozen pizza in the oven and throw the vegetables out.

There are many things that could be done to prevent this waste:
• At the farm level: encourage gleaning so that edible crops are made available to individuals and groups (such as food pantries) that are in need and in a position to harvest them.
• At the community level: encourage the composting of food wastes.
• At the individual level and in schools: teach young people how to cook and how to be creative with that leftover head of broccoli.