... If you get through the first few weeks without too many side-effects that's fine, but otherwise if it just gets worse and worse, it would be best to quit.
...or try what has worked for some others, like increasing your intake of one or more of fat (or decreasing it and perhaps transitioning more slowly by eating some carbs if your system cannot currently digest a lot of fats), iodine, magnesium, water, or salt, depending on your individual needs. These are deficiencies that some ZCers and VLCers have reported. They tend to be people who don't eat a lot of fat, organs, blood, fish, shellfish, seaweed, water, and salt and refuse to take any supplements or get their nutrient levels tested to make sure they get the nutrients they need. Most moderners are not fond of eating raw animal fat, organs, blood, fish heads and edible bones, etc., but these sorts of foods tend to be eaten by carnivorous humans. There are tricks to ZC/VLC that the indigenous Arctic peoples perfected over centuries and millennia and even many of them eat small amounts of berries and other plants, with even the most carnivorous observed Inuit getting 2% of their annual calories from plants, IIRC (though some of the coastal Chukchi may get even less if a documentary I saw is any indication). It shouldn't be done blindly.
