When I started a new game after - around 5 mins real time all 20 of my starting rations disappeared. However almost immediately afterwards 2 of them came back. As you can see I'm still on day one which means I could've at a maximum only eaten 3 rations.
After around 3 mins of playing after this, my rations returned ( the extra 2 are just muckroots)
I paused the game for 3 mins, selected the areas i wanted to dig let the game run and that's when all 20,000 kcal of food (20 rations) disappeared. After that i just let it run some more and the rations came back.