What it says on the tin.
heres a list of what I found that needs adding to.

atum:emmer_bread
atum:camel
atum:camel_cooked
atum:quail
atum:quail_cooked
atum:date
atum:glistering_date
atum:golden_date
atum:golden_date_enchanted
atum:crunchy_scarab
atum:crunchy_golden_scarab

also, is there a way to add values via a json file or perhaps a string array like:
mod:name, group, percentage
group being the name of the food group in the food group config.
percentage being a number between 0 and 100.

probably a server config list or another file in a common file in the config folder somewhere to do custom values for people who end up with mods that don't have values built in already or want to hard customize/rebalance?

also, is there a way to add values via a json file or perhaps a string array like:

Yes. Groups are determined by tags. So just make a datapack and tag items with the appropriate groups. For instance, adding anything to a fruits group would be tagged as diet:fruits.

Overriding the food values used for diet gain is done by using the foodOverrides array in the diet-server.toml file.

oh, so it's two fold? does adding the tag to it just make the percentage appear based on how powerful the food is and divided by the different groups or something?

Yes, the calculations are based off of a "quality" value, which is normally (food gain + (food gain * saturation modifier)). It's not strictly divided by different groups, as there's a penalty deducted for each group it's added to (this penalty is configurable in diet-server.toml as well). The override list can be used to offer another "quality" value instead to any particular item.

roger-roger. I'll go add em to my datapack then. and yep, I saw the penalty percentage, I've actually reduced it slightly already.