According to the Bureau of Labor Statisitcs Consumer Price Indexes, over the past twelve months the cost of food consumed at home has risen by 1.5% in the San Francisco Bay Area (which includes San Francisco and San Jose).
Meanwhile in Los Angeles the same price index has fallen by 0.5%.
Nationally, the U.S. City Average index has fallen by 1.3%.
There is no breakdown of this index available for San Francisco and Los Angeles, so we cannot see how much of the marked difference is due to a different allocation within the average basket of food, and what is due to a rise in prices for similar items.
But if the national indexes are similar to those in California, perhaps the Bay Area is eating more healthily?