As glib as your comment is, the answer is that people will probably start eating at home. I'm not saying they will eat higher quality foods, but they won't be eating fast food as much. The value proposition isn't there.

I see this in my own life. I've eaten out for about 80% of my dinners. Taco Bell use to be $0.89 a taco. Now it's around $2. It took me 15 minutes round trip to get Taco Bell. My time (including fuel for the car) and food costs are now at or below $2 per taco (where I would get at least 3 for myself, two for my wife and 2 burritos betwixt us). I can eat steak and potatoes for the same total cost of a meal.

Homo economicus still has a digestive system. It's now considering the amount of energy (money) required to gather the food. Similar to the homo sapiens idea of, "Should I eat these nuts or get a pack of people to take down a bison?"