The FAO's monthly food price index recorded an average of 196.6 points, down 3.6 percent from July. Meat prices remained strong, with the FAO's meat price index posting 14 percent growth year-on-year.
Read MoreRussia Deputy PM: 'Sanctions not good from any side'
Russia's ban of the import of Western dairy products hit prices, as did easing Chinese imports of whole milk powder.
Prices of wheat also continued to slide in August, after another record year for wheat production meant the grain fell to its lowest value since July 2010. Maize prices also slumped to a four-year low, as ideal growing conditions added to already abundant stocks.
Global cereal inventories are now expected to rise to their highest levels in 15 years. The FAO expects world cereal stocks to reach 616 million tons by the close of the season in 2015 — 12 million tons higher than the previous forecast, and over 6 percent (37 million tons) over stock levels at the start of the 2014-2015 season.
Read More'Parmigiano-Belarussiano' and other secrets of Russian chefsunder food ban
Rice was the only grain to buck the trend in August as Thailand continued to withhold supply from stock piles.
"The fact that Thailand is still limiting sales of the huge rice volume held in public warehouses has been one of the principal factors underpinning world prices in recent months," said FAO economist Concepción Calpe.
—By CNBC's Jenny Cosgrave: Follow her on Twitter @jenny_cosgrave