The UN body said the prices of almost all commodities measured in its Food Price Index dropped last month, including milk, vegetable oils, sugar and cereals.
"Ample supplies, a slump in energy prices and concerns over China's economic slowdown all contributed to the sharpest fall of the FAO Food Price Index in almost seven years," it said in a statement.
In contrast, meat prices in August remained virtually unchanged from the previous month, although overall they are still down 18 percent from the peak of August 2014.