Anybody who thinks that prices for many many things are not being manipulated in a big way is not paying attention.
yes, there is still a strong supply and demand impact on fast turnover low profit items like groceries, and yes most of them are actually low profit for the store itself. But, I trend food prices over time and this whole last year prices have been so far off of what any reasonable economic theory would dictate that it is clear it is not simply supply and demand.
I think most economic theory is malarkey, but basic common sense should be at work and it is not. Flour has been all over the block from $1 for a 5lb bag last christmas to $5.75 this christmas. Usually, some items go up when demand is high, but other items, like flour, usually go down to bring in the buyer who only buys once or twice a year. They make it up in volume.
Monsanto is holding huge quantities of grain and sends it out of the country as it sees the market fluctuate so our supply and demand is only one very small indicator.
Like, here is a good one: Who is the largest oil company in the world?