I have been fermenting vegetables, kimchi for the most part, for a few years and am familiar with the general arc of the process, as well as observing how active my ferment is.
Yesterday, I started a half gallon of sauerkraut, a half gallon of white kimchi, and a couple pints of fermented beets. Today, I am working up nutritional values for each in support of a Keto eating plan. I've had no trouble working up the raw calories, fat, net carbs and protein for each recipe. Yet I know that fermenting will change the carbohydrates and perhaps other values.
I am aware there is no one-size-fits-all for this calculation, rather the opposite, it seems the number of variables is too broad to pin down any kind of equation. Case in point, I have three ferments going, all burning at a different pace. That said, I'm looking for any kind of rough approximation based on experience.
Two facts seem certain. One, that the fermented product will have a lower carbohydrate value than the cumulative raw ingredients. And two, the resulting carbohydrates will never reach zero. That leaves the rate of burn. Based on your experience, what would you expect the carbohydrate burn to be in a highly active ferment for something like Napa Cabbage, Red Cabbage, or Beets?
Less important, but of keen interest, should I expect the other values (cals, fat, or protein) to change as the result of fermentation?