One of the primary factors affecting food security in a given region has to do with the "market driven" aspect of food as a retail product. The selling of food is a business, and that business will seek a market that can not only support it, but allow it to prosper. Those of you who live in urban or suburban areas have seen grocery stores fail or move to another spot, as growth in an area redirects traffic flow. But when you do a market analysis of rural areas, the sparse and decentralized population makes it difficult to find an ideal location for a grocery store, especially the megastores that keep retail prices down through volume buying. The smaller (family-owned) stores don't enjoy savings through volume buying, so their prices are (sometimes considerably) higher.
So, folks who live in rural areas are prone to suffer the same problems with food availability that some impoverished Africans do: there's not enough money to draw the food to them. Whether it's sparse population or not enough change in your pocket, the result is the same. To get the food you need, you have to travel greater distances and/or pay a higher percentage of your income to acquire the food, and when radical spikes in the price of gasoline occur, it drives up food prices and the cost of going to get the food.
While corn-to-ethanol and natural disasters have played a role in Iowa's situation, these things merely exacerbate a food security issue that was already present.