Theory - the lore behind the Shield and the Slurp items
In this post I'll give you my interpretation for the effects of Shield and Slurp items that regenerate the shield and health in the Loop. No need to mention this is just a theory and not everything on it is confirmed.
What is shield?
Shield is an invisible protective field that surrounds the body of the loopers.
What are the shield and slurp effects?
They are the effects of consuming Shield or Slurp items that can regenerate our shield, or shield plus health in case of consuming Slurp items.
How do Shield and Slurp items give us the Shield and Slurp effects?
The looper obtains the effects by natural or processed food that have what I like to call Shield Vitamin, Slurp Vitamin and Slap Vitamin.
What natural food provides shield?
-Shield Mushrooms: mushrooms that have what I call "Shield Vitamin", which only gives you shield.
-Slurp Mushrooms: a mutation of Shield Mushrooms that have a different version of Shield Vitamin called Slurp Vitamin, which can give you both health and shield.
-Slurpfish: a genetically modified species (possibly by the IO) that give you Slurp Vitamin.
-Shield Fish and Jellyfish: two species that, because of their diet, now have Shield Vitamin and Slurp Vitamin inside of them.
-Klomberries: they are full of Slurp Vitamin.
-Slap Berries: they don't have Shield Vitamin nor Slurp Vitamin, but Slap Vitamin.
That's all.
The processed food that gives you these effects, like Slurp Juice or Pizza, do so because of their ingredients, who have the previous mentioned vitamins.
Fun Facts:
-According to one of Metal Team Leader's lines, we can know that Shield Potions are served hot.
-In the Outlandish Oddities Questline in Save the World, when Dennis takes a sip of a fake Slurp Juice he wonders where the "citrusy finish" is. So, thanks to that, we can now confirm Slurp Juice, at least his StW version, has a citrusy finish.