In fact, the price of bread has gone up by three times as much as the extra cost of the wheat in it.
As it happens, I think the cost of tuna in a tin has increased twice as fast in terms of how much of the contents it accounts for. Of course, you always have to bear in mind that there is a lot more in the cost of processed food than raw materials; processing, transport and distributors’ margins to pick out just a few. What one cannot keep track of is the extent to which retailers time their price increases and how much they set off margins on one type of food against another.