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Hello @Christiweger, thanks for joining us, it's great to have you on board!
Indeed, it's possible to add food logs for any other day other than "today". Simply open the app and tap on the food tile.
Then, start logging your food by searching it or selecting it from the recent or custom meals.
Once you've selected the food, choose the serving and then tap on Date to select the exact date which could be "yesterday" or another of your choice.
I hope this can be helpful, give it a try and keep me posted in case you need anything else! 
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