Is there an unsafe fasting glucose level for healthy, non-diabetic adults? On day 2 of a 3 day fast my blood glucose reached 46 mg/dL (ketones high at 7.8 mmol/L). I ended my fast early out of paranoia (and was perhaps looking for an excuse). While its been noted that non-diabetic individuals cannot reach zero on blood glucose, I would guess that my body is not well adjusted enough to keto yet. In your (non-medical advice) opinion, is there a lower level at which I should stop fasting?