The Economist, though starting off with a misleading reference to the horse meat flap in Europe, does a nice job here in its Daily Chart of illustrating why food is so costly to the poor. Were you confused by the stories that explained, way back when, that the riots and political unrest which exploded into what we then called the Arab Spring (now perhaps better dubbed the Arab Turmoil or Festering Wounds) were sparked by food price increases? This may help clear things up.
We all know that food is essential. What we often don’t know is how big a chunk it takes out of a poor person’s daily income.
A related article on why Food Riots Likely to Become the New Normal