Global grain imports have increased more than fivefold over the past half century, stoking fears that countries have become too dependent on the vagaries of international markets for their food, an environmental researcher said.
If prices rise, or wild weather prompts countries to impose grain export bans, as Russia did in 2010, nations heavily dependent on imports could face crisis.
More than a third of countries import at least 25 percent of their grains, an increase of 57 percent since 1961, said Gary Gardner, a researcher at the Worldwatch Institute in Washington.
Thirteen countries were 100 percent dependent on imports for their grain supply by 2013, an 18 percent increase from 1961, said Gardner, author of the report "Food Trade and Self-Sufficiency" published this week.
World grain imports rose from just over 50 million tonnes in 1961 to more than 300 million tonnes in 2013, the report said.
"More and more countries depend on global markets for their food - that creates vulnerability," Gardner told the Thomson Reuters Foundation on Friday.
Russia's 2010 ban was partially responsible for triggering social unrest and a revolution inEgypt as more than 500,000 tonnes were not supplied and global prices rose damaging Egypt's state bread subsidy program, a farm lobby group said.
Global food prices are currently at their lowest levels in more than four-and-a-half years, the U.N.'s Food and Agriculture organisation (FAO) reported this month.
But population growth, expanding appetites for meat in developing countries - which requires grain for feed - and environmental pressures mean this trend won't last forever.
Governments should do their best to protect farmland and water resources, Gardner said, to nurture homegrown production and not just leave food supplies to the mercy of global markets.
The number of hungry people worldwide has dropped by nearly 200 million since 1990 to 805 million in 2014, according to the FAO.
However population pressures and economic growth are leading countries to convert farmland into urban or suburban areas. In the United States alone, agricultural lands the size of Indiana were "paved-over" between 1982 and 2007, Gardner said.
"National agricultural endowments need to be protected," he said. "The market has an important role to play but it shouldn't be the final arbiter of who gets food and where it comes from."