Hal13,
Those are all really good ideas. The hunger/nutrition states and resulting effects you describe are quite clear (I can almost see the code). I applaud your ability to highlight the key conditionals in the middle of a description.
I would not want to try to explain that to a new or young player. I'm also not sure if having the hunger bar lag eating would improve gameplay since people seem to be confused by hidden variables or delays.
The idea of caloric intake requirements being higher when well fed or lower while malnourished is great and would probably not even be consciously noticed but would feel correct.
If the nutrition bars gave a more substantial and obvious benefit (max health, healing rate, speed, etc.) and at the same time dropped more quickly when the hunger bar was empty, people would see an increased value for food. Skipping lunch would not put a normally well fed character in danger (or have the annoying damage sounds), but might undo a day or two of work toward gaining the benefits from improved nutrition.
Just like you said, actual damage (starving) should occur when both the hunger bar and nutrition bars are empty.
Effectively, I see an opportunity in the nutrition bars as a foodstuff differentiated time integrated hunger bars that give meaningful benefits if high. The nutrition bars would be what really affects gameplay, while the primary hunger bar indicates your the opportunity to fill them up.
I'm not aiming at high realism here, just gameplay mechanics that give people another thing to strive toward.
Not that I suggest it, but the different nutrition bars could even give different benefits e.g. protein -> bonus health, fruit -> bonus speed. This verges on "too much of a game mechanic" to me, but some people like that sort of thing and it would encourage a balanced diet. Maybe all nutrition gives bonus health initially and then other different bonuses start above 50% or 75% on a per-bar basis?