I am thinking of taking something like this, but also adding some challenges for balance. For instance, adding in nutrients and calories in different types of foods. The player would have a weight depending on which type of foods they ate and their weight would affect their speed and so on.
To make players want to have different types of foods there could be different aspects added to each food item that would do a player temporary or lasting benefits but also add weight to the player. Like some foods would have not as good benefits but also not add as much weight. While some foods have great benefits, they would add more weight. The player would get rid of weight by exercising and if they got to too low of a weight they would start losing health.
There can be so much done with just this one idea. From just reading this thread I have thought about making a mod that adds more body effects, etc. The only thing I would need is somebody to do the art because I am no artist.