This is only my first day completed of a water fast and I’m already in ketosis. I’m pretty sure because my energy is fine and my tongue is already coated and tastes like metal. Is it because I’ve fasted before in the past and my body is used too it?
People here are confusing ketosis with being fat adapted. You are making ketones all the time, but usually at very very low rates (0.1 mmol/dl). Once fasted after 12 -16 hours, the rate of creation of ketones (ketosis) jumps significantly, somewhere between 1 mmol/DL - 4 mmol/DL.
Once insulin drops, fat burning begins. You would have to be SEVERELY insulin resistant (and likely morbidly obese, which is not impossible) to not be in ketosis after 12-16 hours of fasting.
What did you eat before you started fasting? If you had low carb, then you didn’t have much glucose to burn off, also since you’ve fasted before your body is more likely to recognize the lack of carbs and switch to ketosis.