Does anyone know why it takes so long to get back into ketosis after falling out of ketosis accidentally, or even just getting into it from being on a high carb diet? From what I understand, the liver stores a day’s worth of glycogen, and once I burn through that I should be in ketosis. I have not found that. I can be in ketosis (according to breath meter and general overall feeling of well being), and then I slip up and eat a few too many nuts for example. Suddenly I’m not registering on the breath meter. Then it takes a few days to see a reading again. This doesn’t make sense because even if I had 50 grams of carbs, can’t my body just burn through those in a few hours?
Being fat-adapted (when the body prefers burning fat instead of glycogen for fuel) is my goal and I’m in it for the long haul, but getting kicked out of ketosis seems to be a real setback for me. I’ve been mostly in ketosis for about 4 months.
Can anyone give an explanation? And I love science so you don’t have to dumb it down too much. 
Time to get into ketosis after dropping out
Maybe your body gets the sugar taste and starts converting more protein to glucose through gluconeogenisis. Also, difference in type of ketone component measured in breath or urine than blood levels i think. So, hard to say for sure what’s going on. Maybe nuts kick start your body to use more ketones and nothing left in your breath…but that’s just a shot in the dark. Possibly you are very insulin resistant and your levels don’t decrease for days after spiking. Maybe once they spike, even moderate protein intake keeps them up. I’d be interested in the real answer though if someone smarter has any insight
Dr. Phinney makes it sound as though it can take as long to get back into ketosis as it took the first time, but other people on this forum have posted to the effect that they can slip out and slip back into ketosis with no trouble, once they became fat-adapted.
As I understand it, there are a few issues here: firstly, breath ketones (aceto-acetate, if I remember correctly) are like urine ketones, in the sense that as the body gets better at metabolizing fat, the readings get less over time, and you can be in ketosis and it won’t show on the meter. Secondly, there are questions about just how accurate these meters are anyway. Even the blood meters aren’t as accurate as they could be, apparently. Thirdly, the ketones you measure on the meters are the ones your body hasn’t used yet, so they are not as good an indication of your fat-burning ability as we might like. And it’s burning fat that is the important thing, not the actual level of ketones reported on the meter.
In other words, just do your best and KCKO.