Here is a chart of the BLS CPI index for food only:
What's remarkable is how stable food prices were until the Nixon years and the subsequent skyrocketing of the index. Dumping the Bretton Woods exchange system hasn't been good for the cost of food. Oil prices seem not to have affected this metric as food prices kept rising during the long period of low oil prices in the 1980's and 1990's.
A better phrase for this sort of chart would be a "hockey stick".