Even when I was on strict keto - half and half would not take me out of Ketosis. Starting IF I’ve found the half and half helps me through - then as I progress I start dialing it back towards a true fast. I’m a big fan of using a temporary crutch to get ya going vs going hard to begin. Other’s probs disagree - :) And when I was beginning, the half/half made it very easy to do 19:5 window and then I couldn’t eat all my calories for the day. That’s better than nothing. Just get started and then refine as you go.