Kohaku, I'm afraid I have to distance myself from your nutritional idea.
It would require overtly complex underlying mechanisms noone would be able to remember, and the only visible end result would be that one dwarf eats 3 foods per meal, while another one eats 5.
Which is IMHO wrong! All dwarves need to eat 1 food exactly. The disparity would make the stocks screen and the number of stockpiled food completely useless. The player would have no way to tell how much food there is and how long the stocks will last. Making Dwarf Fortress more obscure is not what we want.
But I'm also afraid Toady agrees with you because I seem to remember he wrote somewhere he wanted to implement a nutritional system. My two cents are: I don't really care about nutritional system, as long as it works in the background, is completely automated and doesn't make the game any more complicated. All I am willing to do is to provide different food sources - if the dwarves handle the rest automatically, so be it. But if I'm required to monitor their food intake, carefully prepare recipes for a balanced diet and whatnot, I'm probably quiting the game.
Not to mention our modern understanding of diet and its components are only recent, and by medieval and whatever, people had no idea (in the better case) or a completely wrong idea (in the worse case) of what was healthy.
--EDIT:
There could be a couple of different nutritions. And a lack of something would make dwarfs more sleepy, lazy, less effective in combat or even make them easily fall for sickness.
This is what I'm afraid of. How would the player know their dwarves are weak due to lack of animal fats or whatever? Is there any simple way to tell them? Or would they have to browse through Thoughts screen or endless tables to find the information amongst dozens of random other numbers or stats? If the latter, don't bother implementing nutrition, it would only made the game worse.
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And even if it is all invisible, there's a problem how to inform player about the nutrition. How would the player know something went wrong? The game really shouldn't have a system with a complexity bigger than it can meaningfully report to the player. Would there be a separate Nutrition screen that would list all dwarves' needs and consumed foods in a similar way how the Healthcare screen now? That would be horrible! A reasonable way to handle the system would be for it to be invisible all the time, unless there is a problem. Then some pupup or something would warn you: "There's a danger of scurvy! Quickly provide more fruit. If you don't do that in two seasons, dwarves might start to die". This would be allright, it's quite user friendly and also provides an interesting challenge.
Now we can feed entire fortress with strawberries with out having to bother with other food too much.
This isn't really a problem with nutrition, and you don't need nutritional system to handle this problem. Is is again a problem of the food units, and how much dwarves consume per year. How much is 1 strawberry? I imagine it would be something like a jar of strawberries. But how can that much be harvested from a single tile? And even if it could, it would just mean that 30 jars of strawberries provide about the same amount of food as a single cow. Which is ridiculous. One dwarf eats 8 times per year, which means that 8 strawberry bushes - or 8 jars of strawberries - provide for a single dwarf for a whole year. Farewell, economy!
The game simply needs better balance of food "sized" all over. And when the foods are balanced in between each other, you then need to balance adventurer mode and fortress mode, because as I've already says, dwarves eating only 8 times a year must consume much more per meal. We probably can't solve that now - we've tried to come up with a division based on how much a single cow would last, but our division wouldn't probably work for grain, cheese, berries, etc. The first step really needs to be to balance the foods so that "1 meat" is about the same amount of food as "1 grain" and "1 berry".
Thinking about berries specifically, I'm not convinced they can be kept in fortress mode. Gathering enough berries even for a single dwarf serving (= 1/8th of a year's food intake) seems extremely difficult, and it wouldn't be worth the effort. For a fortress of 100 dwarves or a human town of 100 people, berries might as well not exist - their effect would be almost nil. Unless, of course, you dedicated a large part of the workforce to gathering, but I doubt any player would want to do that. I see no reason for keeping berries in. They would probably be best as an adventurer mode only and just a cosmetic thing for dwarf mode (like pebbles are).
OR berries could be implemented the same way as spices, if we ever get to that point. I imagine foods like these wouldn't satiate nor decrease hunger, they would only create happy thoughts. (I know, you might argue you can get satiated by berries in real life. But fortress-mode scale is very different from real life or adventure-mode scale).
Killing bacteria by cooking and then storing the meal in barrel for a couple of months doesn't sound reasonable.
As Kotaku said, there are people less concerned about effectivity who build things not because they're effective but because they're pretty, cool, or whatever. I always use dyed clothes only because I can. I decorate as many items as I can. I build nice hallways and rooms, etc. etc.
). I mean, you need glass jars to can things in, right? How common would glass jars be around 1400? Not much I think. So when I wrote "with difficulties and in small amounts", I meant that and should have been more direct. "Small amounts" is to avoid canning whole barrels at once, and "with difficulties" = requires glass jars you need to create in your glass smelter first.
).