Circulatory System is a mod that simulates various organs of the human body.
The idea is to give more depth to Minecraft's effect system and making it so that instead of just being able to consume potions of foods for effects, each player will have to decided how much of a tradeoff they want to take, in the form of getting powerful effects but at the cost of damaging your organs. Having damaged organs will provide you with negative status effects, differing in type and strength depending on the organ. With default configs, reaching 100% heart or brain damage will just outright kill you.
However, using config files and the flexible add-on API - if it may be called that - this mod can be adjusted to be a more general health simulation that punishes you for improper care of your bdoy.
You can sort of think of this mod like Nutrition except with organs and negative effects.