One big hit for me was having to create an entirely new set of recipes when I cut out meat from my diet. It got really hard because plant protein is way different from animal protein. The processed vegetarian stuff is insanely expensive too.
Modding those recipes to replace the dependency on heavily-processed ingredients with the fresh, less-processed comparables readily available today often produces good results, though it does take more time.
[1] - https://archive.org/details/cbk?and%5B%5D=year%3A%221950%22&...