Hunger

Hunger is a derived statistic in Fallout 4 Survival mode and Fallout: The Roleplaying Game.

Gameplay
Hunger occurs if the Sole Survivor does not eat food after a long enough period of time. It accumulates slowly at all times. Increased levels modify SPECIAL stats. Higher hunger levels induces Fatigue, at which Action Points will become affected. Ultimately, damage will be taken, reducing Hit Points. Most types of food will reduce hunger by some amount, though certain foods are more effective than others.

Stages of hunger
There are five stages of hunger that span in-game hours. It doesn't appear that the thresholds are linear. For example, it takes about 6 hours to go from well-fed to peckish to hungry, then 12 hours to go from hungry to famished. The following table shows the approximate times that it takes for a character to go from completely satisfied to the listed condition in each area. In-game time is expressed in "hours" and real-time is expressed in "minutes".