Last month, a United Nations conference in Rome discussed the world's rising food prices.  The group called for trade barriers to be reduced and food export bans to be lifted.  The cost of major food commodities has doubled over the past two years with rice, corn and wheat at record highs.   The Philippines and Haiti, among other countries, have been hard-hit. Some Filipino and Haitian immigrants in the United States are sending food to their families back home.  VOA's Deborah Block has the story.