When you spawn in a new world do you have the max 20 points of saturation? Pretty basic question but I can't seem to find the answer anywhere
According to the Minecraft Wiki:
foodSaturationLevel: The player's current saturation level, which determines how fast the hunger level depletes and is controlled by the kinds of food the player has eaten. Its maximum value always equals foodLevel's value and decreases with the hunger level. Its initial value on world creation is 5.
This means that, when you spawn in a new world, your hidden saturation bar is approximately one quarter full.
I verified this claim myself by creating a new world and running
/data get entity @s foodSaturationLevel, which produced
5.0f as the wiki suggested.