They determine a lot through pricing and decision on availability.

People don't like getting ripped off or paying more than they have to so people, myself included, buy more of whatever they happen to have on sale this week. At our house a lot of decisions on what to have for dinner start by looking through the weekly offers page on the supermarket's app which influences our diet. For instance we eat a lot more chicken than we would do if it wasn't constantly on sale.

Decisions to jack up prices also affect diet. For instance we used to eat a lot of ground beef and sour cream but now it has become so expensive that it is no longer worth what they're charging so we almost never have it anymore.

Availability is also a huge part of the way they determine what we eat. It don't even have to be a food desert to have a huge influence, the convenience of not having to go to more than one shop alone has a huge influence. For instance I like beefsteak tomatoes a lot more for everything where you cut up the tomatoes and don't want the watery seeds. But I eat a lot more plum tomatoes because that's what they have at ordinary supermarkets and I would have to go to the Arab store to get the other ones which would mean I would have to spend 20 minutes more shopping.